Document e7353wg9w3RRZzkQXjMwZzp3y

tlfrj.tTrnru.. ~ffi~JOZWSITOl ~lTIJffllUDG!JUCSillliD~ Manheim, Pa. OIVISION and LOCATION TO: Messrs. G. D'Olier J. F. Glennon J. H. Perry J. E. Day R. L. Ramsey J. R. Roe SUBJECT: DATE: May 4, 1977 Attached Data Sheet #18 from the Occupational Health Branch of the Ontario Ministry of J,abor concerning asbestos may be of interest. I. H. Weaver g:::-!) att. cc: Messrs. J. H. Marsh G. F. Butt E. W. Drislane, FMSI R. H. Mereness, AIA Dr. H. c. Lewinsohn \: II ,I -------- -------------- FMSt 05105 Ontario Ministry of Labour Occupational Health Branch Data Sheet No. 18 ASBESTOS -~----- DESCRIPTION The name comes from the Greek, "unquenchable" or "indestructible". It is a generic terc applied to a number of naturally occurring silicates which can be separated from the parent rock in fibrous form. The common types fall into two categories (a) Serpentine - chrysotile (~6 (OH)S Si4010) (b) Amphiboles - amoeite (Fe5 Mg2 Si 8 o22 (OH) 2) actinolite / 3(C~Si0 .~ Si03 .FcSi03) - anthophyllite ((MgFe) 7 Si8o22 (0H) 2) - crocidolite (Na20.Fe2o3 .3Fe0.8S102 .H20) - tremolite (CaiMg5Si8o22 (0H) 2) The fibres of the d~fferent forms have characteristics - in terms of length. fle~dbility, texture, tensile strength, resistance to heat .or chemical reaction - which make each suitable for particular purposes. The characteriotics which have been most exploited are flame resistance end tensile strength. OCCUPATIONAL EXPOSURE Exposure to asbestos fibre~ ih air can occur in L~ning or milling or in any of hundreds of u9es or processes. The fibrous material may be sprayed &@ insulation. as a fire retBrdant. or for acoustic effect. Asbestos is combined in ceDent asbeatos board. shingles. brake linings. paints. floor tiling. water and sewer pipes, and is used in the production of moulded plastic product8 0 in aheet form as lagging for insulation and in flame rntardnnt cloth. FMSI 05106 '. 2 SOURCE A large proportion of the world's production of chryaotile ia from Canada - mainly QJebec, with some from Dritish Columbia, Yukon Territory, Ontario and Newfoundland. The-USSR is also an important producer. The main source of amphiboles is South Africa. Canada ~orta some crocidolite (blue asbestos) and amoaite (brown asbestos) for apecial processes. Altogether the world production consista of chryaotile 93%, crocidolite 4% and amosite 2% (approximate percentages). Tremolite and actinolite are of little commercial importance but are of health significance as they occur in some tales. HEALTH ASPECTS Yhen air containing asbestos fibres ia inhaled, a number of effects can result. These will vary according to the type, concentration, size of fibreinbnled, the duration of exposure and in some casee to a combined effect with other inhaled contaminants. The principal forms of asbestos-related disease or disorders are: 1. Asbestosis - a diffuse of lung tis-sue. fibrosis {scar_,r.- ing and shrinking) 2. Lung cancer. 3. Mesothelioma - a oalignant tumour of the pleura or peritoneum (lining of chest and abdomen). 4. Cancer of organs other than the respiratory system e.g. gastro-intestinal tract. 5. Pleural thickening and"calcification. Asbestosis The standard for asbestos control in air mentions fibres great~r than 5 micrometers.(5~) in length because it is believed that smaller fibr~s are removed by the ordinary self-clearing mechanism of the lungs. The smaller fibres are generally engulfed by the so-called scavenger cells. Inside theee cells the fibres b_ecoma coated 'orlth proteinaceous material containing iron to form 11 ferruginous bodies" which, if coughed up. can be recognized in the sputum. The ferruginous bodie~ in sputum may be indicative of nsbestos exposure but not necessarily of asbestos related disease. Fibres longer than 5vm have a tendency to be retained in the lung tissue where they may cause irritation and eventual scarring. Over years of exposure this may result in increaBing shortness of breath. Advanced asbe9tosis can be diagnosed by chest x-rays but at a much earlier stage, the disease may be recognized by pulmonary function (breathing) tests. Lung Cancer FMSI 05107 The incidence of lung cancer is much higher in asbestos workers than in the general population. Lung cancer in asbestos workers is usually '' 3 preceded by fibrous changes in the lung tissue as occurs in asbestosis. It is claimed that an asbestos worKer who smokes has 92 times greater chance of acquiring lung cancer than a non-smoking, non-asbestos vorker. (8) Note - There is evidence in the literature that mineral fibres other than those ot asbestos e.g. -wollastonite, attapulgite, fibre glass and rock wool, may act on the respiratory organs in a manner similar to asbestos fibres. Mesothelioma In the general population this is a rare maiignant tumour. It has, however, been shown that a large proportion of the people who develop it have had some exposure to asbestos, though not always an occupational eXposure. There appears to be a latent period of over 20 years between the first exposure and the appearance of the tumour. There is some evidence that mesothelioma is more likely to be caused by amphiboles (such as crocidolite and amosite) than by chrysotile.(lO) Cancer of Organs Other Than the Respiratory System AD increased occurrence of cancers in other locations than the respiratory system e.g. the gastro-intestinal tract, the breaat(6,7), has been reported. This is apparently due to the capability of the asbestos fibre to penetrate the lung tissue and to reach othe<r organs outside the cht:llt ~vity, or the:. asbe:.stos fibres ~:.wallowed with muccus :m3 !eel! tc penetrate the walls of the stomach and intestines.{9) Pleural Thickening and Calcification Asbestos fibres may cause irritation, inflammation and thickening of the pleura (pleural plaques). This is a condition that c~~ be seen at x-ray examination. It is evidence of prolonged exposure to asbestos but is not necessarily associated with symptoms of ill-health. STANDARD The time-weighted average (TWA) refers to the airborne concentration of substances in the workplace air. It is the concentration for a normal 8-hour workday or 40-hour workweek, to which nearly all workers may be repeatedly exposed, day aft~r day, without adverse effect. The maximum allowable concentration (t~C) is the maximum concentration of airborne substances in the workplace air to which a worker may ba exposed: such an exposure shal~ not exceed more than one 15-minute period per day. For chryaotile - TWA is 2 fibres greater than 5vm in length pe~ cubic centimetre(cc). MAC is 10 fibres greater than 5~m in length per cc. FMSI 05108 For amphiboles - TWA is 0.2 fibres greater than 5~m in length per cc. MAC is 2.0 fibres greater than 5VID in length per cc. The TWA of 2 fibres per cc. is intended to control the risk of asbestosis to less than 1%. For sampling technique, see Appen~ix 1. ,. -~------ CONTROLS ! General 1. Personal Hygiene (a) Good personal hygiene is to be maintained. This includes washing before eating, drinking, smoking or use of toilet facilities. *(b) Change Rooms - are to be provided by the employer at a fixed place of employment for workers working regularly at the place and who are exposed to airbo~ne concentrations of asbestos fibres. *(c) Clothes Lockers - two separate lockers for each worker so separated by a shower room that one locker for otreet clothes is in one room and a second locker for work clothes in another room. Contaminated clothing is to be placed in a covered impermeable container. (d) -Laundry (1) Laundering of asbestos-contaminated clothing is to be done so as to prevent the release of airborne asbestos fibres in excess of the TWA. (11) An employer who gives asbestos-contaminated clothing to another person or company for laundering is to inform such person or company of the requirement in subsection (1) of the subdivision. (iii} Contaminated clothing is to be transported in sealed impermeable bags, or other closed iapermeable container and a caution label affixed (see Section 3(b){i). 2. Food, B~veragcs and Tobacco Food, beverages and tobacco are not to be kept nor consumed in the work area. FMSI 05109 *Note - For workers eng3ged in work other than at a fixed. location, e.g. in~ulntors, alternative suitable arrnngementr nr~ to be provid~d. J .. 3. Caution Signs and Labels (a) Caution Signs - Post~ng - Caution signs are to be provided and posted at the approaches to each location where there is significant exposure to asbestos fibres._ The sign is to be printed in English and, as necessary, in other languages so that all workers understand the hazard. A typical asbestos card is shown as Appendix 2. (b) Cautiqp Labels - (1) Labelling - Caution labels are to be affixed to all raw materials, mixtures, scrap, vaste, debris and other products containing asbestos fibres, or to their containers, except that no label is required where asbestos fibres have been modified by a bonding agent, coating, binder or other ~aaterial so that during any reasonably foreseeable use, handling, storage, disposal, processing or transportation, no airborne concentrations of asbestos fibres in excess of the TWA will be released. (ii) Labels - All labels are to be in accordance with the Guidelines for the Labelling of Toxic Chemicals for Use in Ontario Industry. 4. Special Clothing _,. The employer is to provide and to require the use of special clothing, head coverings, gloves anJ foot coverings for workers exposed to airborne concentrations of asbestos fibres. 5. Work Practices Work practices are to be followed, as completely as possible, that prevent the dissemination of dust. Examples are:- (a) When dumping bags of asbestos: (1) Local exhaust is to be used. (11) E~cessivt shaking of bags is to be avoided. (iii) BagB arc to be disposed of carefully using local exhauot, covered containers, plastic bags that can be sealed, etc. (b) When sawing, drilling, srinding, machining asbestos-containing oaterials, etc. (1) Local exhaust ia to be used (ii) Products are to be vacuum cleaned, ~ashed, or otherwise cleaned before further operations,. storage or shipping. . Compressed air is not to be used for cleaning. FMSI 05110 ' '. 6 -: 6. Housekeeping Housekeeping includes prompt vacuum cleaning or wet sweeping of all scrap& and spills, careful storage and disposal of asbestos-containing materials in plastic bags or other suitable containers, and frequent and regular cleaning of cachines, floors, walls and other plant surface& (by vacuum cleaning) ~here asbestos dust &ettlee, Dry sweeping, dusting or compressed air are never acceptable, 7. Personal Protection In certain circumstances and for limited perioda of time, the worker may be protected by respiratory equipment. This should, however, never be allowed to take the place of adequate environmental control, It muot be recognized that the wearing of a respirator fot long periods of time is often uncomfortable and sometimes of questionable efficiency. Workers may, in some instances, be neglectful in the care and the use of their respirators, thus decreasing the reliability of this type of protection. In general, air levels below the standard of 2 fibres pet cubic centimetre are to be maintained. During process changes or while improvements are being made to a plant, workers may be required to wear replaceable filter t)~e respirators of the type approved for control of respirable dust if fibre concentrati.ons do not exceed 10 /. fibres per cubic centimetre. This is always to be considered a temporary measure and is not to be continued beyond three months. During such periods it is essential that the wearing and the maintenance of respirators be closely supervised by the employer. B. Engineering Normal procedures for the control of respirable dust apply to the control o[ the health hazard from asbestos. 1. Substitution ~~en feasible, asbestos should be replaced by lesa hazardous materials. 2. Segregation It io possible with suitable planning to arrange that work producing high concentrations of asbestos dust is done in isolation. Where segregation is difficult. as in the case of asbestos spraying, it is possible with suitable scheduling to have the proceso carried out when other workers are either off the shift or when they are removed from the area. Control booths, under positive pressure. may isolate the worker from exposure while allowing him to control a process. In certain circumstances. respirators may also be used (see 10~ersons.l Protection"). FMSI 05111 7 3. Ventilation The use of adequate local exhaust is the most important method of dust control. This method captures the dust at the source &nd conveys it to a central dust collecting system. Good general exhaust is to be provided so that any fibreo not captured by local exhaust are eventually removed from the workroom air. .. --~---~ 4. Dust Suppression The use of water to suppress dust at the source has been universally accepted. Water sprays are perhaps the most common method of applying wate~ to control both visible and respirable duet but it is not possible to control a dust cloud by means of water sprays once the dust has become airborne. C. Medical Surveillance l. First Aid No acute poisoning due to asbestos has been recorded. 2. Preplacement Medical Examination Preplacement medical examination is to be done within 30 days of the person's employment in an e>:posure to asbestos. The eY.amination is to include a medical and occupational history including smoking habitm; pulmonary, cardiovascular and gastro-intestinal symptoms; a physical examination; n cheat x-ray (posterior - anterior, 14 inches x 17 inches); and pulmonary function tests to include forced vital-capacity (FVC), and forced expiratory volume at one second . (FEVl.O). 3. Periodic Medical Examination Periodic medical examination is to be done at least every two(2) yeora on each employee engaged in an occupation exposed to asbestos fibreo. Tho examinatioq is to follow the same procedures as outlined for a preplaceQent medical examination. It is to be noted, however, that tho&ft persons who (a) have a history of 10 or more years of employment involving exposure to asbestos, (b) show x-ray findings (such ~s small opacities, pleural plaques, pleural thickening, pleural calcification) which suggest or indicate pneumoconiosis or other reactions to asbestos, or (c) have changes in pulmonary function which indicates restrictive or obstructive lung disease are to have the chest x-rays and pulmonary function tests at least Annually. FMSI 05112 --------------------------------------------------- 8 ' 4. Termination Medical Examination " Within thirty(JO) days before or after termination of employment, an employee engaged in an occupation exposed to significant airborne concentrations of asbestos fibre is to have a termination medical examination. The examination is to follow the same -- --------- procedure as outlined for a preplacement medical examination. 5. Medical Records Complete a' nd accurate recorda of medical examinations are to be maintained. These confidential records are to.be reta1ned1Py the employer for a period of forty(40) years or length of employment plus 20 years whichever is longer. AC'I'ION LEVELS Depending on the process, it may be difficult for an asbestos-. producing or using industry to meet the standard at all times. It becomes necessary, therefore, to establish criteria on which certain actions are to be taken. It is desirable that work plnces be mon~tored and exposure of personnel be determined regularly. The aim must be to keep both area 3nd personal samples below the TWA. ~~cnever the standard is exceeded, personnel are to be protected by the wearing of approved respirators until the conditions are corrected. As indicated above (see Personal Protection), this action io acceptable for limited periods of time, when concentrations are between the TWA and the t~C. At the same time, it is the responsibility of management to advise the representative of the Ministry of Labour that a state of no~-compliancc exists. When the concentration exceeds the MAC the process is to be shut-dawn while corrective &ction is taken. At such times only workers with positive pressure air-supplied respirators are to be engaged in repair or corrective work. The representative of the Ministry of Labour is to be notified and will decide whether or not the work may resume. As a general rule, the mill or plant will not be allowed to maintain production if the asbestos exposure exceeds the MAC. At levels bet~een TWA and MAC production may be allowed to continue on condition that the workers wear appropriate respiratory protection, that positive action is undertaken by the firm to correct the situation and that the period of corrective action does not ~xceed three months FMSI 05113 BIEL J.OGRAPHY 1. Enterline, Philip E.: Pitfalls in Epidemiological Research: J~ Examination of the Asbestos Literature Journal of Occupational Medicine/Val. 18, No. 3/March 1976. 2, Rajhans, G.S. and G.M. Bragg, Ph.D.: -A Statistical Analysis of Asbestos ~iber Counting in the Laboratory and Industrial Environment, American Industrial Hygiene Association Journal, December 1975. 3. Edwards, G.H. 'and J.R. Lynch: The Method Used by the U.S. Public Health Service for Enumeration of Asbestos Dust on Membrane Filters, Ann. Occup. Hyg. Vol. 11 pp 1-6 (1968). 4. Code of Federal Regulations, Part 1910.1001 Occupational Safety and Health Administration, Department of Labour, U. S. A. Revised as of July 1, 1975. 5. Occupational Exposure to Asbestos ,.. U. S. DepBrtm~nt of Health: Ed1H'ation and WelfarE' Uational Institute for Occupational Safety and Health, 1972. 6. Selikoff, I.J., Hammond, E.c Churg, J . : Mortality experiences of asbestos insulation workers 1943-1968 in Pneumoconiosis Proceedings of the International Conference, Johannesbrg, 1969 Oxf~rd University Press. 1970. 7. I. Doniach, K.V. Swetteriham and M.K.S. Hathorn: Prevalence of Asbestos Bodies in a Necropsy Series in East London, Association vith Disease Occupations of Domicilliary Address B. J. of Ind. lwd. 32-16-30/75. 8. Selikoff, I.J., E.C. Hammond, J. Churg- Asbestos Exposure, Smoking and Neoplasia, JAJ~ 204/106-112/1968 9. Toll: The Age Distribution of Cancer. Implicationo for Models of Carcinogenesis, J.R. Stat. Soc. 134/1971 10. McDonald, J.c . McDonald, A.D., Gibbs, G.W., Licmiatiski, J. and Rossiter, C.E.: Mortality in Chrysotile Asbestos ~nes and Mill& in Quebec, Arch. Envir. Health 22-(677-686) 1971. FMSI 05114 . '. t APPENDIX I ...: . Sampling Techn~que for Asbestos in Workplace Air The ideal sampling period to determine a TWA is a full shift, however, this is rarely practicable. It has been demonstrated that a 90 Dinute sample gives a reasonably accurate estimate of the TWA particularly if the process is a constnutione. The more continuous the process. the 11\ore representative a short tenu sampling will be. lt is evident that the skill of the sampler operator and a familiarity with the process are i~portant factors in the asscssmenr of an asbestos exposure. The rate of sampling may vary between 1.8 and 3.0 litres per minute depending on the airborne concentration of .asbeatos fibres. The counting method uoed is that of Edwards and Lyncb.(l) A segment of the filter is placed on n glass slide and treated to make the filter transparent. Counting of the fibres is done with an optical microscope using phase contrast illumination at 400 to 430 X magnification. The special counting graticule has reference marks which permit a rapid classification of fibres (a "fibre" is described as being over SJ,!m iu length and having an aspect ratio of 3 to 1). The procedure is to count 100 fibres or 20 fields, whichever is less. A simple conversion is then made from the counts per field of view to fibres per cubic centimetre. Sampling f re<!~'ency :1 A to bP. ttdar>ted to 1'!eet the nee..11 of th~ local situation. During a start-up period or during a process cb&nge, frequent s&mpling may be required. The actual time interval~ll depend on the judgment of the person making the assessment. NOTE: The l-linistry of Labour recognizes that there can be considerable variability of fibre counts done by different operators in tba same situation. In the hands of a skilled operator the reproducibility of the results can be expected to be at least 25% (plus or minus).(2) Ho~ever, the actual fibre concentration in the air will also vary throughout a workday and the results of a sampling period of less than a full 8-hours requires interpretation by au experienced industrial hygienist. The Ministty recognizes, also, that there is a need for additional research to establish the validity of counting procedures as well as the relative significance of area and personal samples FMSI 05115 APPENDIX 11 " DUST HAZARD ASBESTOS DUST MAY BE. HARMFUl TO YOUR HEALTH AVOID BREATHING DUST WEAR ASSIGNED PROTECTIVE EQUIP~fiENT . DO NOT REMAIN IN AREA UNLESS YOUR WORi< REQ,UIRES IT FMSI 05116 I I l ! I 1 t f ! I 1 ! I 1 ' ASBESTOS INFORMATION ASSOCiATION/ North America . 1835 K Street,. N. W. Suite 4 ? Washington. D. C, 20005 This study develops a decision method for evaluating the social acceptability of industrial controls on hazardous materials. Decisions are based on a ..multiple criteria approach .. ihat}ointly considers measures such as risk-benefit tradeoff, minimum . reducible health risk, maximum acceptable cost andimplicit value of human life. Health risks are calculated by combining separate estimates of production and usage patterns, emissions to air and water, effectiveness of controls. pollutant dispersion and human susceptibility. Economic benefits consideremployment, trade and consumer impacts, as well as direct costs ofcontrols. The analysis focuses on asbestos as an example hazard. Relative values of hazard reduction alternatives are examined for asbestos manufacturing exhaust filters and for asbestos substitutes in brake linings. Preliminary calculations indicate risk reductions of these alternatives cannot justify their social costs. Risk-benefit analysis for industrial and social needs KENDALL D. MOLL and DENNIS P. TIHANSKY: Stanford Research Institute; George Washington University 1 .. - The term risk-benefit analysis has become a commonplace expression as both the public and governmental agencies become increasingly concerned with- environmental protection and the quality of life. Attendent with this concept is the notion that there is some sort ofsheet used in the decision-making process for regulating environmental quality. Informal comparisons of risk~ and benefits do indeed occur in setting most regulations. The underlying decision structure, however, does not always incorporate three crucial considerations: the necessity of making tradeoffs; the likelihood that tradeoff impacts are noncommensurate (that is not expressed in the same units, as dollar benefits vs. loss of life); and uncertainty about impacts of alt~rnative decisions. Formal riskbenefit analysis is useful here because it systematically applies economic theory and decision analysis to help the _policymaker understand the tradeoffs. Risk-benefit analysis has different comparisons for different persons. Some ecologists, for irc>cnt adJrn~: Castle and CoClLt. Inc... San Francisco~ CA. example, value preservation of nature over costs of control; they might think it meaningless to compare ecological parameters with any economic concept. On the other hand, many industrialists place greater weight on the costs of preserving nature. Uncertainties or perhaps even ignorance of environmental consequences, can significantly affect an individual's value system. Fear of unknown risks often instills greater conservatism in action than is warranted by the objective situation. For instance, a minute but well publicized probability of death from exposure to a hazardous material might make an unknov.ing person think that he will be affected. Aggregated over all individuals, this risk could thus be exaggerated over its actual level. Publicity about risks and benefits could also be a poor indicator of individual values. Surveys are thus important in assessing variations of public opinion. patterns of risk-taking among membas of the general population and perceptions of risks and benefits. A large spread of personal evaluations should be exp~cted given data deficiencies on risks and benefits. Information about ambient concentra- American lndus!rial Hygiene Associalion JOURNAL (381 4171 FMSI 05117 153 tions of hazardous materials and the degree of human exposure is not generally available. More fundamental is the lack of information on inherent biological effects of these chemicals on human health. Epidemiological studies have been outstripped by the technology to produce and distribute an ever growing number of hazardous materials. For some new chemicals, the regulatory agency relies on the manufacturer and developer of derived products to furnish health information. But without a character or checklist of needs for conducting risk assessments, the manufacturer cannot really be expected to assume this additional responsibility. PRESENT STANDARDS INDUSTRIAL POLLUTION ALTERt~ATIVE CONTROLS ECONOMIC BEliEF ITS EXPOSURE HAZARDS HEALTH RISKS Insights on benefits of product use are typically as deficient as judgements on hazard levels. Conditions for optimality in regulation depend on the "welfare function.. to be maximized. O~e criterion frequently employed is maximum value of total output, which in principle should include such non-monetary aspects as safety, aesthetic qualities and reductions in physic tension or anxiety. Economists generally contend that these benefits of controlling hazards can be assessed collectively as the sum of the ..willingness-to-pay.. of all individuals affected by the action. Analytically, this requires the formulation of a consumer demand curve for feasible controls. Benefit assessment then involves integration of the area under this curve. Determination of the overall curve relating benefits to emission control policies requires a multi-step analysis, in which the economics input occurs only after exposures and health effects have been determined. Consequently, the lack of benefit estimates for regulations can be only partly blamed on economists. The lack of meaningful exposure and dose-response relationships falls in the domain of the life and physical sciences. Without accurate knowledge of these relationships, attachment of economic values is a misleading and perhaps futile exercise. Most regulatory agencies as well as researchers lack an appreciation of the complexities underlying benefit estimation. As a result, they tend to establish controls which minimize risks without explicitly considering product benefits. "Zero-tolerance law~," which MULTIPLE CRITERIA PRESENTATION Figure 7-Risk/benefit methodology: Analytir:af Steps. prohibit any detectable amount of a hazardous material, are inflexible and can quickly become too costly. They may obligate large budgets; they may remain ineffectoveranextended time span; and they may adversely affect the lives of many individuals. Although risk-benefit analysis should make decision-making more comprehensive, there are a number of limitations to its current usefulness. First, it represents an abstraction of reality and is usually simplistic. It may not be translatable into practice if it does not adequately account for all impacts. Second, the magnitude of uncertainity about both risks and benefits is typically much greater than the magnitude of their most likely values. This difficulty emerges as the most severe constraint of any formal analysis. Proxy measures are often used to measure impacts..and these proxies may be quite crude. Some authors, for example, represent risk in terms of death rates.1 While vital, this measure fails to incorporate non-fatal results that are .likely to be far more prevalent and in some cases more damaging in total than the number of deaths. Another limitation is that risks and benefits of various actions do not usually come in single pairs. Rather, each control level implies a diversity of beneficial and costly impacts. The analyst, with limited resources and time. must 154 Am. Ind. Hyg. /!.ssoc. J (38) April, 19n select the those of more, l another , risks. In< evaluation needs and There t limitatior Because l risk-benefi vehicular~ for auto investigati of hazard: struck ~ person- and a ! individua, ratio. 1 Th1 as the mo willing to A not he represer, consu. risk~ corn::: additio11 claims, bt. public reft the exist1 acceptanc was not d In the 1 new appr incorpora American Indus ----------.. ----.--.- ~ ---~-""-""- ... -- .._... FMSI 05118 STANDARDS: ] J J IS. 'us ne ey m; ny ke 1re ss. i is 1t0 all tity 1Ch ely ere IXY md JrS. ath to )be ore th;;_ sof tlg_k sa The 1U5t Figure 2-Hazardous waste system. select the most important impacts and exclude those of hopefully less importance. As he learns more, he may change the list of impacts. Still another limitation concerns weights assigned to inrisks. Individuals seem to waver their evaluation of generally low-probability events as needs and perspectives fluctuate. There have been few attempts to consider such limitations in formal risk-benefit analyses. Because highway data are readily available, risk-benefit studies are inost numerous for vehicular accidents and choices of safety features for automobiles, (e.g.). 2' 3 One extensive investigation of risk-benefit ratios for a number of hazardous events, such as driving and being struck by lightning selected "fatalities per person-hour of exposure" as the measure of risk and a bc;nefit index defined as "value to the individual" in the denominator of a risk-benefit ratio. 1 The benefit in most cases was quantified as the monetary investment that consumers are willing to support for a risky venture. Another more formal, theoretical model represents benefits of an item as the price a consumer is willing to pay for it.4 As hazards or risks increase with item use, its value declines correspondingly. However, there is an additional "non-pecuniary" part of risk, he claims, beyond which the consumer or general public refuses to buy or use the item. This implies the existence of a threshold level of risk acceptance. Whether such a level actually exists was not demonstrated. In the remainder of this paper, we present a new approach toward risk-benefit analysis. It incorporates risk and benefit comparisons, as in the above referenced s: -.:dies. But it goes beyond their scope by including uncertainty factors and by showing how various decision-making approaches can result in different priorities. The conceptual model to be presented was applied to a selection of feasible controls on hazardous materials, namely, cadmium and asbestos usage in the United States.~ The methodology follows very closely that recommended in the recent National Academy of Sciences report on Decision Making for Regulating Chemicals in the Environment.6 The most significant aspect of this methodology is its reliance on a "multiple criteria" approach. A multiple criteria approach involves the consideration of many factors bearing on the decision in addition to those of "risk" and ~benefit," such as "minimum reducible risk," "maximum socially acceptable risk,""maximum acceptable cost," and "value of human life." As shown in Figure I, the analysis starts with a review of present standards and proceeds to parallel examinations of the existing pollution s,.-stem and alternative controls that might be a'pplied to it. The parallel approach continues with second stage investigations of economic benefits on one branch and of population exposures and resultant health hazards on the other. Finally, the economic benefits and the health risks are combined with other relevant parameters in a graphical presentation of the multiple criteria affecting the decision. This presentation is applied under a variety of possible decision rules to derive acceptable standards and develop priority research needs for future improvement of the decisions. Am~:scan lnduslrial Hygiene Associalion JOURNAl/381 4177 155 - FMSI 05119 STA!il iUS DISPO:i~L ____j WASTEj AIR tA!1ijt~IID PRODUCTION r-- ----"INlHG -j-11-1t-~:-~;-------- PII~~97: ;s3.288 11s "e r-------~~~~77.~~~----. j i 153 24io?; iS3 42 39 4 210 ZJ j I 14 z I' 1e 4 7I CONTRC ORIGit. CONTRC: EFF. NATIO. 129 28. I I I i I I 1llTAL Figure 3-U. S. Asbestos flow {metric tons per year}. When we examine the top box, Present Standards, in more detail, we discover the kindof control system illustrated in Figure 2. This figure shows how various types of standards impinge on the hazardous waste system and on the monitoring and control mechanisms that accompany it. Standards must be compared with the actual amount of hazardous waste present at a given point in the hazardo~s waste flow system._ For example, production standards must be compared with some measure of the actual production. The difference between the standard and actual production is used as a signal for the monitor and its control system to implement corrective measures if necessary. The same kind of feedback control must operate for usage standards, emission standards, ambient air or water standards, exposure standards and ingestion standards. Note from the figure however, that controls do not have to be applied at the same point that the monitoring signal is obser>ed. Excessive exposures, for example, could be corrected by more restrictive controls over emissions concentrations. These multiple feedback possibilities allow for very complex control systems. The multiple feedback loops do impose two requirements on the monitoring and control systems. \Vhatever standards are developed must be measureable and they must be consistent with other standards that they may be applied at other points in the control process. For example, the OSHA asbestos standard \..-as reduced from 5 visible fibers to 2 fibers per milliliter on July I, 1976. However, the visual methods currently used to count asbestos concentrations account for less than 5% of total fibers and no one knows whether the visual identifiable fibers affect health more than the smaller fibers.' Standards cannot be made very precise until this conversion problem is solved. \Vhen we decide that some measure of pollution, say weight, is most meaningful, then the second step is to analyze the industrial pollution of various media (air, ~ater, and land) that occurs at different stages of the system, from extraction to final disposal. These amounts are shown in Figure 3. We have used a materials balance approach to estimate the amounts of asbestos going to each use and each disposal media and reconcile their totals with our best estimates of overall use and disposal. The quantities (not all of which are shown in the figure) therefore are additive both vertically and horizonatally along the different flow paths. This requires some very difficult data search and 156 Am. Ind. Hyg. Assoc. J. tJSJ April. 1971 Figur~ reco11 creati Howt. miss IJ the d.: plausi systt high! J be ret; basel In l . dispo' pollut' tion i fabric: exam!' also h~ the sc. emissi< brake l effectiv polluti' steps, manure fabric control 96% of n::!tiom about million Subs brake l American 1: . - - - ..- - - .. -- .~,.. ~. l':"''~ __ , -~--- .. - b-~ _ _ ..,..,... _ _ _ __ , _ _ _ _ _ _ _ _ ~.--- - ~ . .- - FMSI 05120 .' E."'ISSION SOURCE: ~.ANUFACTURHlG FACILITIES AUTOMO!IILE BRAKES CONTROL t!ETHOD: F.;BRIC FILTERS SUBSTITUTE MATERIAL ORIGI~AL E~ISSIONS: 5!J7 METRIC TONS 129 METRIC TONS COilTROL EFFECT 1VENESS ! 96% 100% NATlONAL COST: LOW MEAN HIGH S2.5 ~ILL ION $3 $3.6 $52 MILLION $65 $81 Figure 4-Asbestos control costs and effectiveness. reconciliation work, almost to the point of being creative when the data is particularly sparse. However, we feel it is necessary in order not to miss large parts of the problem simply because the data is difficult to obtain. It gives us a plausible base from which to make an overall systems analysis and, at the same time, highlights areas where existing data may need to be refined. It also provides a first-order priority base for examining alternative controls. In our analysis, we observe that although land disposal accounts for the great bulk of asbestos pollution, the largest source of air contamination is the 547 metric tons emitted from fabrication 'operations. We therefore have examined controls for asbestos fabricators. We also have examined the possibility ofeliminating the second most significant airborne source: emissions from users of friction products (i.e., brake linings). Economic costs and operational effectiveness of control alternatives for these two pollution sources were examined in the next two steps. as shown in Figure 4. For asbestos manufacturing processes, we ascertained that fabric filters are the most effective method to control emissions.8 They can eliminate about 96~(; of stack emissions. We estimated the total national cost for such a program would run about S2 million per year, plus another $1 million for monitoring and enforcement. Substitution of other materials for asbestos brake linings is speculative since no satisfactory IC-:.0 .. , JI ;------ "..a..:'.. [ ~ .. t:0: u I 'FROM ...u:.:.:_0 ":r' '~[ < t"z"0'' <z L ,.Ltz .0.. o i .a<.:. :z: "uz' 0 u g r ~ GOt !J 100 1000 10,000 AREAS EXPOSED- SQUARE KILOMETERS Figure 5-Asbestos a1i concentrations. material has yet been found. But if one assumes that a material can be found for a 50% cost increase, the total extra cost would run to about $65 million per year. These economic costs have to be balanced against the control program's reduction in public exposure and consequent hazard, which we also examined. Figure 5 shows the total areas now exposed in the U.S. to various concentration levels from industrial sources and from brake lining emissions, according to our simplified model of emission sources and air dispersion. Note that industrial sources are more concentrated over a smaller area than are brakeshoe sources. Total exposure to the population is about 80 mg/ m1 from each source. The big hurdle in our analysis, as in most such analyses, came in trying to develop a doseresponse function to evaluate the effects of these exposures. To do this, we looked at death rate estimates for the three most important causes of death from asbestos: mesothelioma, other cancers and non-cancer respiratory diseases. ;.r..eucan lodusuial Hygiene Association JOURNAL 138! 4177 157 --~ ::H -l -_--_ - --:----: . FMSI 05121 . : l.----.----.-----.----.----.-----~---, 16 :::Q 14- f t~ 12 .:;: ; 10 ~ :8 .~.. .."~' 6 ... ~ ... 4 f I UPPER I CuNFIDEHC I LIMIT I f II : I 1 1 I I II I I / I l I l....' I , '~~ /J LO,.;:R / coFI c~cE I 'ILl:'Hl / I : Jl j I I I I I '! ~I ,,'1 ] --------/ ,/__~_/,/. ...... _.... --' o0 1000 2000 3000 ~000 !,QQ:) ~JC ';":Y.) FIBER- ves/cc . Figure 6-Asbestos dose-response: respiratory system disease. 20~----~----~----~--~-,------r-----, I I 18 I 16 ~ ...~ >< 14 ."-.'.' ~ 12 ~ Q ~ 10 .."..'.. .. 8. ::< 3 EQ 6 u 1:\ UPPER / CONF I DU~CEJ LIMIT 1 I I I I I I I I I I I I I I I I I I I I ...-LOWER CONFIDC:IICE ...... Llrtl:J:,.. ... _....- / ............-" I _....- 1 ......... .,2 I _....,... I ..,.,.,.,..,...,... ,..... 100 I~ 200 FIBER - YEMSfct Figure 8-Asbes/os dose response: mesothelioma. Figure 6 shows excess deaths versus 9r-----.-----.------r----~-----.-----, accumulated asbestos dosage for non-cancer respiratory diseases.9 As with most of our data, /8 I .c.. 7 "0 ' f< w ILl 6 <..0....!. UPPER I CONF lD<'NCE f LIMIT 1 I I I I I I I I f ffi 4 J ~I ;':: I ~3 J / / ,/ "~' I I , .,.,.,-" "' z 1I .,. ... _....- I, ,,1/ II / /' / / // / ~wu / COIIF lO~'IC~ / LIHio we had some problems here in converting from one set of measures and dosage assumptions to another. For Figure 6, uncertainties in these conversion factors were the major uncertainties in determining the confidence limits that are shown. Figure 7 illustrates excess death rates of people exposed to asbestos from all cancers except mesothelioma9 The Mae West shape is simply a matter of curve fitting and has no known physiological basis.. Excess deaths from mesothelioma only are shown in Figure 8. This diagram presents the widest uncertainty of all because its two references 10 ' 11 both attributed their original data to a common source but differed by a factor of five in their resultant calculations. By summing these three causes ofexcess death I and combining their uncertainties as OL-----L-----L-----L---~L---~~---J o aooo 2ooo 3ooo .;ooo 50J-) c:o:oo FIBER- YEARS/Cc Figure 7 -Asbestos dose-response: cancer (except mesothelioma). independent random variables, we arrived at the overall dose-response curves of Figure 9. We show these for analytical purposes as straight lines emanating from the zero intercept, 158 Am. Ind. Hyg. Assoc. J. (38/ April. 19;"7 ., FMSI 05122 ~' ' I although in fact we have no strong basis for assuming that the mean value is a straight line or that the uncertainties arc fixed fractions of the dosage. Mesothelioma appears to be the most significant contributor to the total excess death rate. Asbestosis produces a significant number of illnesses in addition to the excess deaths, but morbidity effects were not included in our analysis. Hanrds from ingestion of food and water were likewise not considered, since most studies of relative ltazards indicate that the principal mode of er of retained asbestos is via the lungs.'~ Finally, we did not consider the effect of population mobility on the hazard. even though people \Vith high exposures are statistically very unlikely to live next to an asbestos factory for their entire lives. But these neglected effects are all relatively insignificant compared to the order-ofmagnitude uncertainties and the other difficulties of reaching a tradeoff between risks and benefits. An overall method of evaluating and presenting risk,'benefit tradeoffs is illustrated in Figure 10. Here, the two main parameters are measured in the separate dimension of the chart. The vertical scale shows risk in terms of Ji,es saved by a control alternatiYe relative to the existing "status quo" situation and the horizontal shows negative economic benefit (or cost) involved. Each alternative, surrounded by an ellipse representing the confidence limits, can be shown in terms of this tradeoff of lives versus nonhealth economic benefits. The dollar tradeoff between health and economic effects is not charted. but any particular valuation of human life can be represented by a diagonal line originating at the status quo position. Alt~rnati,cs lying above this tradeoff line would be- cost-effecti,-c in terms of that particular life ,-:,Juation. whereas alternatives below the line would presumably not be. Other constraints can also be shown on the chart: these act to restrict the feasible domain with which altcrnatiw solutions may be sought. At the top a "minimum reducible risk'" line r..:-prescnts a limit in the number of lives that ...,.. IS ~ 2.0 X ."....'.. "X' 15 1- < ~ ..."~' ~ 1.0 !'!l~LIG~.\ll-YEARS PER CUBIC IIETER IN AIR Figure 9-Asbestos dose-response: total IIINIMUII REDUCIBLE RISK / LIMIT / .,.,..---... / ,,.... ...,/"'.... >< "' L!Mli ,'', /' I ,' I ALTERNATIVE A \ I ,\ ,_. 3en ;.~ E~tlA."..'. > :::; T Tl VE B II II 10 I :, .f.!M/E ,/~' \/ ,: ./1 / : g .... ,MEA.'l I / \,_.,,I ..._.<.,/ "/ ~~ '-,_ ,.,.. ---- ._J ",<_'. ."..-. u u .:f-/ < a"-/ .;:a'/~/ ~:./-" / - ' ~~XI~UM ACCEPTABLE SOCIAL RISK / V'sT.\ 7 ..:~ ;to CO!>T (r;0li-HEALTH DOLLAR BENEFITS) Figure 10-Mu/tiple criteria comparison merhod. might be saved by any feasible alternative. The minimum reducible risk might be considered as a background level of contamination below which further reductions arc extremely difficult. At the opposite side of the feasible domain. the "maxir.mm acceptable social risk" represents a ~"'"Ca1 '"~-sinal Hyg;ene As;ociation JOURNAL (38) 41i7 159 FMSI 05123 ... SAVIIIG 20 10- ~ ~5 :..:.; .a.. :>; z ~ FJLTERS ON ~ FACTORIES/"~\ to - II \~ II I ~I OS II \I \I \..,. .f SUBSTilUI< f~\ BRAKE I ~.ATERI:.~s I \/ I II :I I ~.. ~ ~V \ I -1; ...L(c, ~ .._..0. ~" -\ I '- I ~~-t-'" 10 zo 50 ~ATIONAL COST PER YEAR (MILLION S) 100 Figure 11 -Asbestos pollution control alternatives. number of lives lost that will _not be readily accepted by society. The maximum risk might be some vague social limit such as the prevailing rate of disease, or it may represent a "'h:!re and now.. risk limit as defined by existing standards and regulations. Another constraint, not usually mentioned together with risk limits but nevertheless logically comparable, is that of ''maximum acceptable social cost." This represents the maximum expenditure that society is willing to obligate at a particular time to solve a particular pollution problem. Equity considerations among the population are also now generally accepted as valid constraints. Equity considerations can be considered by making comparable charts for the analysis of each ethnic, income, geographic, generational, or other identifiable interest group. Together, the risk, benefit, and other constraints make up the "multiple criteria" problem. limits of about a factor of two in each direction. But implementation costs ofthetwoalt-:.:matives differ by more than 20: I. If one wishes to assign a value to saving lives, the chart shows that the factory filter alternative costs less than SIO million per life saved whereas brake substitution costs about $100 million per life.. Neither alternative comes close to the $300,000 valuation that workers in hazardous occupations implicity give to their own lives 1 ~' 16 (see the upper diagonal line). For this reason, both alternatives appear inefficient as measures for protecting the general public, if economic tradeoffs are considered. As always in such studies, however, we must qualify our conclusions. First, we have not considered potential effects of these measures on the health of industrial workers, which very likely would be more signifi_cant than those to the general public. Inhalation hazards to brake shoe installers, for example, would be completely eliminated by substitution of some other material for asbestos in brakes. Second, we have only examined two alternatives. Calculations based on our exposure model indicate that about 37 people per year could potentially be saved by eliminating asbestos from our ambient air (see top horizontal line in Figure 11). This potential life saving is SO times as great as we get from either of the two alternatives considered, so additional protection possibilities certainly are worth investigating. These and other factors that go beyond the assumptions of a particular analysis almost need to be considered by decision-makers in real life. Therefore, no single chart can give a complete answer. In addition to the formal trade-off charts of the type shown in Figures 10 and 11, a full presentation should include the listing of many supplementary criteria by which decision makers or other interested parties can derive their own values. Such a list is shown in Figure 12.6 ' When we apply this methodology to the asbestos control alternatives we obtain Figure 11, which has been derived specially for this paper. The first feature one notices in this logarithmic scaled chart is that lives Sa\'ed by the two alternatives are about the same: namdy. 0.6 person per year each, give or take confidence Choices among the criteria presented can be made on the basis of many decision procedures. including those of expected value and ordinan old fashioned biases such as optimism". pessimism and probability. So many selection methods arc available, in fact, that decision makers in some ways will have greater freedom 160 Am. Ind. Hyg. Assoc J (381 A~ril. 19;-;" FMSI 05124 COM.'IENTS NO i ;:;;.r::~ : o?i Hm : ::.i-:=: J:... : co~a~OL REGULATION BA~f Ji.jft . :. S 1 I. HAz;.qos AVO l DED " HEALTH B. ErN!Rm;~;,:r,TAL II. COSTS OF CO:HROL A, DIRECT 8. IrlDlRECT c. HARKH STRUCTU?.E I I I. BEliEF l TS LOST IV. DISTRIBUTIC~ OF BENEFITS & COST I I I Figure 12-Display of benefits and costs. of action than they ever had before. The choice among alternatives may remain ambiguous. But at least decision makers will have explicit, quantitative means for weighing the practical tradeoffs that in the long run are going to have to be considered. references 1. Staff, C.: Social Benefit Versus Technological Risk. Sci. 165:1232 (1969) 2. lave, LB. and W.E. Wever: A Benefit-Cost Analysis of Auto S alety Features. Appl Econ. 2:1 (1970). 3. Ca1ibresi, G.: The Cost of Accidents. Yale University Press. New Haven. Conn."(1970). 4. Muehlhouse. C.O.: Risk-Benefit Analysis in Decision-making. National Bureau of Standards. Washington. D.C.. unpublished manuscript (1972). 5. Moll, K.D. S. Baum. E. Cepener, F.S. Dresch end R.M. \/\/right: Hazardous Wastes: A Risk-Benefit Framework Applied to Cadmium and Asbestos. Stanford Research Institute for Environmental Protection Agency (September 1975). 6. Davies. J.C. ed: Decision Making for Regulating Chemicals in the Environment. Chapter 5 and Appendix H. National Academy of Sciences. Washington. D.C. {1975). 7. Background Information on the Development of National Emission Standards for Hazardous Air Pollu!ants: Asbestos. Beryllium. and Mercury. APTD1503. Office of Air and Water Programs. U. S. Environmental Protection Agency, p. 34 (March 1973). 8. Paddock. R.E. et a/:Comprehensive Study of Specified Air Pollution Sources to Assess the Economic l:npect of Air Quality Standards. Vol. II. Asbestos. Beryllium. Mercury. PB-222 858. prepared for U.S. Environmental Protection Agency by Research Triangle Institute (August 1972). 9. Enterline. P P. DeCoufle and V. Henderson: Mortality in Relation to Occupational Exposure in the Asbestos lr.dustry. J. Occup. Med. 14:897 (1 972). 10. Bruckman. l. and R.A. Rubino: Rationale Behind a Proposed ASbestos Air Quality Standard No. 74-222. presented at the 67th Annual Meeting of the Air Pollution Control Association. Denver, Colorado (9- 13 June 1974). 11. Selikoff. I.J.: Asbestos Criteria Document Highlights. ASS J. (3}:26 (1974). 12. A Study of the Problem of Asbestos in Water. by the American Water \'1/orks Association Research Foundation. AM. Water Works Assoc. Vol. 66. No. 9. Part 2. p. 1 (September 1974). 13. Merliss. R.R.: Talc-Treated Rice and Japanese Stomach Cancer. Sci. 173:1141 (1971). 14. Masson. T.J . F.W. McKay and R.W Miller: Asbestos-Like Fibers in Duluth Water SupplyRelation to Cancer Mortality J. Am. Med. Assoc. 228:1019 0974). 15. Thaler. R. and S. Rosen: The Value of Saving a Life: Evidence f:om the labor Market. paper presented 30 November 1973. published by University of Rochester. 16. M elinek. S .J .: A Method of Evaluating Human Life for Economic Purposes. Fire Research Note No. 950. Herts. En:;;land (November 1972). Accept~ t....;;-s~ 29 1976 I f.. .; '. --- . t f :;;.. ~ .-~ .~ t -..~ ~ ~ :t ... # - ~~:.:.o lo~u~lrial Hygi>r.e Association JOUf!)oJ.;L (38) 4/Tl 161 FMSI 05125 -. 1~ ' A method is described for calculating confidence intervals for particle or fiber.concentration, and for dust collector penetration. Tfie span of the interval depends upon the value of ii fiber concentration or collector penetration reported and upon the number of particles or fibres counted. ~ !' Uncertainty in particle counting and sizing procedures DAVID LEITH and MELVIN W. FIRST Harvard School of Public Health, Department of Environmental Health Sciences, Boston, Massachusetts 02115 l Introduction a representative number of fields under the microscope. All particles seen are segregated The concentration of particles in a gas can be into convenient, continuous size categories. determined by passing a known gas volume Subsequent traverses note entries for only i through a filter and counting particles on those size ranges in which particles are present representative filter portions. Particle concen- in relatively small numbers~ The average num- II I I x,i ! lI trations are valuable to determine compliance with legal standards, as for asbestos fibers in workroom air, or to determine the particle size collection efficiency of a dust collection device by making counts of simultaneous upstream and downstream samples. For both applica- ber of particles in each size range per traverse, is then calculated as shown in Table I. Stratified counting is a way to emphasize those particles whose concentrations arc most difficult to assess with statistical reliability because ., tions, it is important to estimate the count of their relative rarity. reliability. Although enough particles must be counted to establish the validity of the result Nomenclature within acceptable limits, it is wasteful to insist upon excessive counting to obtain needlessly A - inverse of the fraction of total filter high reliability. area examined per traverse Particles for microscopic counting are G -inverse of the total volume of gas conveniently collected on membrane filters1.2 passed through a filter or electron miscroscope grids13.4. The "stratifi- m - number of an equal area, counting cation" particle counting methodS-7 illustrated outward from filter center I in Table I is often used to reduce counting M -total number of equal areas into. I time. An initial traverse is made by examining which a filter is divided I I I David Leith, Assistant Profes sor at the Harvard Uni- Melvin W. First, Professor of Environmental Health versity School of Public Engineering at the Harvard Health. holds Bachelors and University School of Public Masters degrees in chem Health, is a diplomate of leal engineering from the the American Academy of University of Cincinnati. Environmental Engineers and a Doctorate in Environ and a Director of the Amer- mental Health Sciences ican Board of Industrial from Harvard. His interests Hygiene. Or. First was a Oi lie in industrial hygiene rector of AIHA from 1964 and air pollution control. l967. American Industrial Hygiene Association Journal FMSI 05126 '' I I cal C" TRAVERSE 1 2 3 4 5 6 Total, N Mean Count per Traverse, X Std. Deviation of Mean. o; 95% Confidence Interval TABLE I Data Tabulation for Particle Sizing by Stratified CountlngS PARTICLE SIZE RANGE, MICROMI::TERS < 0.45- 0.63 0.89- 1.30. 1.80. 2.5D- 3.50. 5.00- 0.44 0.62 0.88 1.29 1.79 2.49 3.49 4.99 7.09 57 87 54 36 21 24 6 12 0 12 6 3 3 2 2 1 57 87 54 36 21 24 18 18 11 7.10. TOTAL PER 10.00 TRAVERSE 3 300 0 21 03 13 13 23 1 333 57 87 54 36 21 24 9 9 1.8 1.2 300 7.55 9.33 72 105 to to 42 69 7.35 68 to 40 6.00 48 to 24 4.58 30 h 12 4.90 34 to 15 2.12 13 to 4.8 2.12 13 to 4.8 0.55 2.9 to 0.7 0.45 2.1 to 0.3 n -number of traverses performed in a filter directly downstream of the gas inlet. slr2tified counting procedure Dennis and cc,>-workers8 found that such radial N -total number of particles of a certain concentration gradients did not occur for size counted through an traverses particles smaJJer than 20 micrometers diameter Ndown - N for filter downstream of a particle coJJ.:ctor Nup - N for filter upstream of a particle collector P - number of particles per volume of gas P:town - P for gas downstream of a particle collector pup - p for gas upstream of a particle coJJector Pt - dustcoJJector penetration (1-efficiency), Pdown/Pup when filter holders were used which had a ten degree included angle between gas inlet and filter surface. However, filter holders of this design are not always practical because of their large size. To avoid bias when using a conventional holder with smaJJ inlet, fields are usually ., selected at random from a pie shaped piece of the circular filter paper. About twenty fields must be examined2 to complete one unbiased estimate of the particle size distribution. Totally random field selection gives an unbiased estimate of particle concentration when rm . -distance from center of filter to a sufficiently large number of fields is ex- -point where microscope is to be amined. However, the same result can be focused for equal area m obtained with fewer fields by an ordered ap- rr - radius of filter proach. Because the pressure drop across a_ x - number of particles in a certain size membrane filter is 'Sufficient to assure uniform range present in one traverse gas velocity normal to the filter surface, the x - mear: nurr.ber of p~rticles in a certain size range found per traverse volume of gas flowing through each equa.J. concentric area on the filter will be the same, unless the central areas become plugged be- u - standard deviation of x cause of excessive particle deposition there. ur: - standard deviation of i The overall dust concentration for the gas UPt -standard deviation of Pt sampled will be the average of the concentra- tions found in the gas passing through each of the equal areas. To utilize an ordered approach, the microscope should be focused Microscopic field selection at the center of each equal area ring present in the sector, and a single field examined. j .' When a filter holder has a smaJJ diameter in- After one field in each equal area has been Jet relative to the filter diameter, the largest inspected, all data can be combined to make particles may concentrate on that part of the an entry for one traverse, as shown in Table I. February, 1976 FMSI 05127 l' Additional traverses arc made along different comprising in traverses. A Poisson distribution !Ir' radii of the filter sector. describes the variation in these x values 12-14 ~ This equal. area traverse method for locating counting fields is analogous to the method used for positioning a pilot-static tube when determining the average gas velocity in The standard deviation of these values, u, therefore equals the square root of the mean number ~particles in that size range per traverse, x, i.e. I ' a round duct. Average gas velocity could be determined by measuring the velocity at many (2) random points within the duct cross section and averaging the results found. However, the number of measurements needed to reach the same statistical reliability using this approach is greater than for the equal area method, and the random approach is not used. By analogy, Thi standard deviation of the mean, ui , is the standard deviation, u, divided by the square root of n, the number of traverses. 17X = '\jJn;;2 = '\jrnT (3) it is as logical to use an ordered approach for locating counting fields on a membrane filter From Equations 2 and 3, as it is to use it for locating pitot-static measuring points in a duct. The distance, rm, from the center of a u~=,f ~-=I~ x " nx '\J <4> filter of radius rr to the midpoint of each of M equal areas can be found from where N is the total sum of all particles in a certain size range counted through all traverses.. I Tm _ /2m- 1 f, -, 2M Equation 4 is an application to stratified (1) counting of the expression given by Chapman and Ruhf for the relative error associated with Here, m is the number assigned to an equal area, starting from the filter_ center and counting outwards. Alternatively, values can be found in a reference giving the relative distance from the wall at which a pitot probe should be placed in order to have an unbiased estimate of average gas velocity in a circular duct.910 repeated counts of particles in liquid suspen- sion. IS Appropriate values for the standard de- viation of the mean, ux: , are given for the data shown in Table I. The number concentration of particles in a certain size range, P, is proportional to x, the mean number of particles of this size per traverse, to the inverse, Ap~rotfrathveerfsrea,catinodn of to total filter area examined the inverse, G, of the total 95% confidence intervals =xAfter. stratified counting procedures have been gas volume passed through the filter. P AG (5) employed and mean concentrations for particles in each size range calculated, it is important to determine confidence intervals for these values. Systematic sources of error such as anisokinetic sampling. inaccuracies of flow measuring de- The standard deviation of a product can be ( :x ufound from16 2= ( /)I= ( 2AA~) u~) + vices, improper microscope calibration and ~ht: like can be minimized through careful cxpenmental technique.11 Assignment of particles to 2 ( u; ) 2+ ( uGG ) (~ improper size categories is not a significant problem when trained observers use a standard Porton graticule for determining particle diameter. 1~ A source of non-systematic sampling error that cannot be eliminated by control of experimental procedures is associated with random variations in the number, x, of particles in a certain size range which are present in each traverse of a stratified counting procedure With careful technique, the standard error associated with A and G can be made small compared to that for x. The substitution of Equation 4 into Equation 6 gives the relative standard er.ror associated with a measurement of concentration, P. ; =If (7) i ~! American Industrial HJ&iane Association Journal 105 - - . --..----~---- ~ -,.. -~ .-- -- FMSI 05128 ... ' ~ u ~ ~ 0.1 bL5 ! ~ ~oa25~uu~ro~~~-LLL~.oo~~~~~~rooo NlNBER OF PARTICLES CCUfl'0. N Figure 1-Number of particles counted versus relative error of particle concentration. 1000 ::::E Cl ...1a<:.1 Ua.l :::;) z 0 a. :> _, -UlZ 1&.1 100 ua:: iag=:_:"tf-i' l5 a: jg ::::E i NUMBER OF PARTICLES ON DOWNSTREAM FILTER, Ndown Figure 2-Number of particles of one size counted on downstream filter versus number of particles of that size counted on upstream filter, with relative error of pe.netration as parameter. A 95% confidence interval about P will extend plus and minus 1.96 times the standard deviation for P. P 1.96 P v'l/N (ti) Figure 1 is a plot of the relative standard error of particle concei!tration, Up/P, against the number of particles counted, N. Applications When asbestos fibers are counted to determine compliance .with an applicable standard, it is prudent to determine periodically the mean fiber concentration and associated confidence J interval. The count shoul~ be continued only until the standard is no longer contained within the confidence interval, as one can then state with 95% certainty whether or not the standard has been met. When the fiber concentration is close to the standard, it will be necessary to count a larger number of particles to establish with 95% confidence whether or not the standard is met, than when the concentration is clearly well above or below the standa4. For example, after counting 50 asbestos fibers on a membrane filter, one might find that the mean concentration in the air passed through the filter was 1.5 fibers/cc. Equation 8 and Figure I show 'that one can state "with 95% confidence that the true fiber concentration was 1.5 1.96 X 1.5 X (1/50)11., or from 1.08 to 1.92 fibers/cc. The upper bound of the confidence interval for this example is below the 1976 OSHA standard of 2.0 fibers/ cc. Counting additional fibers would make the 95% confidence interval smaller, but would be unnecessary if 95% confidence that the standard is met is sufficient. Equation 4 can also be used to determine confidence intervals about an experimentally determined value for dust collector penetration or efficiency. Penetration for particles of a. certain size is the ratio of particle concentration in the downstream gas to the analogous concentration in the upstream gas. P ...... P t -- -P- (9) The standard deviation of this quotient is111 aPdown1P.,0 ) 2 =(~) 2 =(~) 2 + ( PdowniPuo Pt Puo aPdown ) 2 ( Pdown (10) The substitution of Equation 7 into Equation 10 yields O' Pt p - t'\_J /t N.. + 1 N ...... (II) Therefore, a 95% confidence interval about Pt will extend plus and minus 1.96 times the standard deviation of Pt, as shown in Equation 12. +Pt 1.96 Pt y'l/N 1/N..,... (12) 106 FebruaiJ, 1171 FMSI 05129 ''~ d ( ir AI '-.. ., \ ... Equation 11 indicates that the relative error in penetration for particles of a certain size is only a function of the total number of particles of that size counted upstream, N""' and downstream, Nr~,wn, of the collector. This relationship is plotted in Figure 2. determined by counting. The techniques outlined above can be used for data from automatic counting devices such as optical instruments working on light scattering principles, as well as for data from other automatic counting devices. Equation 11 and Figure 2 show, for ex. ample, that to be 95% confident that pentration of particles in a certain size range is between 40 and 60% ( 1.96 CTPl = 10% with mean penetration of 50%) it will be necessary to count 200 particles in this size range on the upstream filter and 200 particles in the same size range on the downstream filter. Alternatively, 500 particles counted upstream and 125 downstream would give the same result. However, the fewest total particles thzt must be counted to achieve a given relative error in penetration will always be found when the number of particles counted on the upstream and downstream filters is equal. This can be proven by differentiating Equation 11 with respect to Nup, setting the derivative equal to zero, and proceeding in the usual manner. When the particle deposit is less dense on the downstream filter, it becomes necessary to make more tra\'erses for that filter in order to count about the same number of particles as are counted on the upstream. Or, a larger field size could be used for the less dense filter. When the particles observed on a filter are separated into many size categories to determine collector particle size efficiency, it is ;.ecessary to observe a large total number of particl~s to generate adequate confidence in the penetration or efficiency results for each size range considered. When it is desirable to maintain a 95% confidence interval of constant size, i.e. a constant va1ue of CTPt for all size ranges, Equation 12 shows that fewer particles need be counted in each size range as penetration decreases. The stratified counting technique can be used' with good effect to concentrate ~he microscopist's efforts on the size ranges where penetration is high. Therefore, it is worthwhile to identify these size ranges as soon as possible by making a preliminary estimate of penetration based on an initial traverse of the upstream and downstream filters. This method of calculating confidence intervals applies whenever con~entrations are Summary An equal area traverse method is described for selecting microscopic fields when counting particles or fibers on a membrane filter. This method is analogous to that used to position a pitot-static tube in a duct when determining average gas velocity. The equal area traverse approach is an aid in avoiding inadvertent counting bias due to nonrandom field selection. Although confidence intervals are important to establish the significance of particle concentration or collector efficiency data, they are seldom calculated or reported. When particle size data are generated by a stratified counting procedure, the method described can be used to establish with 95% confidence whether or not mean concentrations are below or above a fixed value. Confidence intervals about values of penetration or efficiency can be calculated in a similar manner. The stratified counting approach allows ~he microscopist's efforts to be concentrated onto those particle size ranges where small confidence intervals for penetration are the most difficult to achieve. Charts have been prepared that make it possible to determine easily the number of particles or fibers which must be counted to assure desired confidence intervals. References J. SILVERMAN, L., C. E. BILLINGS and M. W. FIRST: Particle Si1.e A nal~sis in llulustrial Hy~:iclle. Academic Press, New York ( 1971 ). 2. EDWARDS, G. H. and J. II.. LYNCH: The Method Used by the U. S. Public Health Service for Enumeration of Asbestos Dust on Membrane Filters. A"'' Occup. Hyg. 11 :I ( 1968). 3. MORROW, P. E. and T. T. 1\Jl'RCER: A Point to Plane Electrostatic PrecipiHitor for Particle Size Sampling. Am. Ind. H.\'R A.~.wc. J. 25:8 (1964). 4. BILLINGS, C. E. and L. SILVERMAN: Aerosol Sampling for Electron Microscopy. J. Air Pollut. Control Assoc. 12:586 (1962). American Industrial Hyaiene Association Journal 107 FMSI 05130 5. SIClll'L. 11. s.: On the Size Distribution of Airborne Mine Dust. J. S. A/r. l11st. Min. Met. 58:l1l (1957). 6. HOEL.P. G.: lntroductiOII to Mat//t'lllatica/ Statistic'.f. Wiley. New York ( 1949). 7. WHITBY. K. T.: Detami11atio11 of Particle Si:.e Di.ttrihmion-Af1pmaflts tllltl Tec;hlliqllt'S for Flour Mill Dust. Univ. of Minn. Eng. Expt Station Bull. No. 32 (Janu;~ry, 1950). 8. DENNIS. R., L. SILVERMAN, C. E. BILLINGS, E. KRISTAL. D. M. ANDERSON AND P. DRINKER: Air Clttmin~: StuJie.f Progrtss Report for l11ly /, 1955 to Ju11e 30, 1956. A. E: C. Contract No. AT(J0-1 )841 (March 16, 1959). 9. American Conference of Governmental Industrial Hygenists: Industrial Ventilation. 13th ed. P. 0. Box453, Lansing, Michigan (1974). 10. HEMEON, w. c.: Pft~nt mrd Process Ventilation. 2nd ed. Industrial Pras, New York (1963) .. II. HAWKSLEY, P. G. W .. S. liADZIOCit ancJ J. It, lli.ACKETT: Mm.fllrcmt'llt of Stllitl.f ill Fl11e GQ.Ses. British Coal Utilization Research Assn., Leatherhead, Surrey, England (1961 ) 12. FAIRS. G. L.: XII-Develormcnts in the Technique of Particle-size AnalyKis by Microscopical Examination. J. Ro_, Microscop. Soc. 71:209 (1951). 13. CORN. M.: Statistical Reliability of Particle Size Distributions Determined by Microscopic Techniques. Am. I11J. Hyg. Assoc. J. 26:8 {196S). 14. IIERDAN, G.: Small Parricle Statistics. 2nd ed. Academic Press, New York (1960). IS. CHAPMAN, H. M. and R. C. RUHF: Dust CountinJ Reliability. Am. InJ. Hyg. Assoc. Quart. 16:201 ( 195S). 16. AllO.:IN. H. and R. R. COLTON: Statistical Methods. 5th ed. 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February, 1976 I ! FMSI 05131 "- l . -.-- _.... .. ,1975 nt in V. P. 'lt"alt/J Arllll. I. lly ;onna Mark: Counting Asbestos Fibers by the M'ost Probable Nu1nhcr Method l,ARKER C. REIST,&:.D. D"pnrtm"lll of Erll'irolllllt"lltnl Scit"IIC":S tllld E11gi11uri11g, Unirr.fity of Nort/1 Caroli11a, Clu1pd Tlill, Nort/1 Carolina 27514 A procedure for nalualing a.<;be!ifos riber count!i Is described which uses the most probable number method of bacteria counliug. This lechuique is faster than comen tlonal counting methods, willa approximately comparable accuracie~o, allbough it surfers from a hack of rl(:or 1md requires the ob!lienoer to estimate t"iher concentralion.oc to "'ilbln an order of magnitude before counting. For the routine assessment of a large number of a.~be!ifos l'illlDples this procedure would seem to be more desirable than conventional counlina because of the economy of time as well as being easier on the obscrver. ' : Introduction RECENT FINDINGS ON THE TOXICITY of asbestos have led to increased interest in sampling and analytical procedures for determining the concentration of asbestos fibers in air. The Occupational Safety and Health Administration has established an interim eight-hour time weighed average airborne allowable concentration of five asbestos fibers greater than 5 microns length per cubic centimeter of air, and this standaro will be lowered to 2 fibers/em' on July l, 1976. Evaluation of asbestos fiber concentralions in air is carried out using samples collected on membrane fillers ~nd viewed with phase contrast illumination .at 400X-450X.'2 This method is the standard field sampling method adopted by the Public Health Service. Fibers arc assumed to be distributed randomly over the filter surface and at least 20 but no more than 100 fields arc to be. viewed. At least 100 fibers arc counted which gives a 95% confidence limit of 20%. Because o( the relatively small amount of sample colleclcd, more than J00 fields would have to' be viewed if one were to find 100 Cibcrs on a 10 minute sn~1plc collected at a rate of 2 liters per minute from air containing 5 fibers (5 microns length) per milliliter, and if the concentration were only 2 fibers per milliter, 435 fields would have to be assessed.3 Of course, the: number of fields necessary could be decreased. }>y in creasing the sampling time-i~:H tl!e Jatier case a 90 minute sample would yield 100 fibers in 50 fields--but the flexibility of short-term samples is then lost. . 1 Counting fibers is a tedious and timeconsuming business fraught with a number of subjective decisions for the micrOscopist to make. For example, in the case of two fibers lying side by side he must decide when a fiber is a fiber or when it is only a large particle. (It is considered that any par- ticle having an aspect ratio of three or greater is a ~ibcr). If ihc sample is relatively light, a great deal of information is lost which actually can be used to determine fiber density. Besides actually counting the number o{ fibers, then:: is another quite distinct statistical method which could be used for estimating the number of fiber~ randomly distributed over a surface, the so-called most probable number method. In this paper the method will be applied to asbestos fiber counting 379 --,_ FMS\ 05132 ~I 380 May,191S ;md the advantages and limitations of its usc will be di5eusscd. Theory The concept of the most probable number method for csitmating randomly distributed number densities was first described by McCrady4 and more recently by Cochran~ and principally was applied to the problem of estimating bacterial densities. Chapman' applied the method to dust counting but it was not received with much enthusiasm for reasons which will be discussed later. Most recently the technique has fallen into disfavor even for estimating bacterial conccntrations in milk and water samples, mainly because of the advent of more direct membrane filter techniques. For fiber counting however, the method appears promising because it eliminates the need to resolve individual fibers and with the low densities normally found, gives the same counting accuracy in a much shorter period of time and with much less eyestrain. Consider a filter of area A which is 'broken up into a fields. 1f there arc m fibers dis- tributed randomly over the filter surface, then the average number of ribcn; per field, /,is I =.!!! a (1) The probability, P, lhan n fibers lie in a cer- tain field can be expressed using the Poisson relationship ---- (2) .. . provided that a is a large number. The probability of a field being void of fibers is, from above P(o) = e-1 . (3) If the void fields are distributed randomly across the filter and L fields arc sampled, the probability that exactly I of these fields will be void is Ll Pa(o) = /! (L - I)! [P(o)]' [ 1 - P(o)] ,,. -1) (4) Equation 4 gives a distribution of probabililies which is very small for small l and rises TABLE I 95% Confillence Interval for a Given Average Number of Particles Per Field Particles/Field True Average L,. 25 95% Confidence Interval Expres.~cd as a Percentage of the True Average (left column, minus; right column, plus) L .. SO L = 100 L = 200 0.1 0.2 0.3 0.4 o.s 0.6 0.7 0.8 0.9 1.1 1.2 1.3 . 1.4 u 1.6 1.7 1.8 1.9 2 100 229.1 76.6- 156 69.6 - 111.3 54.8- 90.3 S6.3- 79.4 52.7- 76.2 47.S- SS.2 4S.6- 73.8 44.3- 75.6 43.2- 51.5 -75.8- 138 58 79.7 49.9- 58.8 42.1- 59.8 41.1- S2 37.4- 40.8 3S.6- 47.4 33.6- 38.8 32.8- 38.9 32.2- 39.7 56.1- 84.9 41.3- 51.7 34.1 - 43.1 31.5 - 36 27.8- 36.2 27.9- 33.6 23.9- 32.2 2S.1 - 31.S 22.3- 31.4 21.9- 31.7 23.9-28.7 21.8- 29.6 22 -26.8 23.3-28.4 22.6-29.9 20.9- 26.8 21.4- 28.7 22.1 -25.6 20.2 - 33.1 23.5- 30.3 43.3 - 51.1 29.8- 3S 25.9- 28.1 23.1 - 2S.S 21.8- 22.6 18.7- 22.8 18.8 - 21.7 18.1 - 21.2 17.6- 19.4 17.4 -19.S 17.4- 18.1 16.3- 18.5 . 16.S- 19.2 15.6- 18.1, 15.9- 19 16.3- 17.9 16.8-19 16 -20 15.2-21.4 15.7-20.2 Amnlcar I lo some small aj lhut havj Turning concentl I The a pic proc tion. A dctermir present 1 the natu fields sc fields co 1 most p~ can be I As th creased,\ creases. i range fol at variot Equatior 100 fiel 30% regardle~ provided density i Figure miciU5COJl FMSI 05133 :L I I Amrrirtm ltu/u.ttrilllllyl[irnr A.unciatitm Jmmwl to some maximum ;aluc hdorc becoming small again: The most likely probability, tlmt having the largest value, occurs ut I = Le-I (5) Turning this around, the most probable fiber concentration is thus f = ln (~I ) (6) The above development results in a simple procedure for assessing fiber concentration. A number of fields arc scanned to determine only whether fibers arc or are not present in any given field. Then by taking the natural Jog of the ratio of the number of fields scanned divided by the number of fields containing no fibers (Equation 6) the most probable number of fibers per field can be estimated. As the number of fields scanned is increased, the accuracy of the estimate increases. Table I shows the 95% probability range for scans of 20, 50, 100 and 200 fields at various fiber densities, as calculated from Equation 6. Thus, for example. assaying 100 fields will yield results within about 30% of the true value 95% o the time, regardless of the total number of fibers seen, provided, of course, that the average fiber density is somewhere around two fibers per Figure 1. Variou~ orienlntions of fibcn in the micnl!IC"op.: fio:ld. 3RI field or less. Assaying 200 fields will in.crcasc the accuracy o[ the 95% confidence interval to something less than 20% nf the true count. For the case o( L = 2QO, the accuracy a-ppears to increase with an increasing avcmge number of; particles per field. This-Will continue until the point is reached where there is a good chance that every field contains at least one fiber. This occurs when the average number of fibers per field is slightly in excess of three. Thus for this method it is necessary to estimate ahead of time the fiber concentration to within one order of magnitude so that there will be about 0.2 to 2 fibers per field, or, if there appear to be plenty of fibers in evidence, to then usc the direct count method. Of course, the number of fibers per field can be easily varied by changing the field size. Definilion of a Field Conlaining a Fiber Thus far,. for the purpose of development of the theory, fibers have been considered as if they were particles. But they are not. A fiber has length and as such may stan-in one field, extend through another or several others and fina1ly terminate in yet another field. Figure 1 illustrates such a situation. The fiber originates in the upper ]eft hand corner, continues through the lower left hand corner and then ends in the lower right hand corner. The fiber in the upper right corner represents no problem. There arc several ways in which the fiber that passes through several fields can be treated. First, only the lower (or upper) end of the fiber can be considered, and the field th:1t it lies in then is a field not devoid of fibers. In the rare case where the fiber is perfectly horizontal, some convention. such as choosing the left hand side of the fiber would be appropriate. A field would be considered. blank i( the lower end of n fiber were not in it. Thus, in Figure I, only the fields on the upper right hand side and lower right hand side would J:>e considered, to contain fibers. Since each fiber is asso- FMSI 05134 -1 382 ci~llcd with one "lower" end, the estimated number ends would eqm1lthe estimated number or fibers. A second approach would be to call a field void only if it contained no fiber ei1ds at all. In Figure 1only the lower left hand field would be considered to be void. The most probable number of ends would then he estimated and since each fiber has two ends, the m_ost probable number of fibers would be the estimated number of ends divided by two. An obvious disadvantage of this approach is that the upper limit of density which could be used is half of what otherwise would be used. The most reasonable approach is to assess only one end of the fiber. If the fiber is a bundle with a rough end lying on the edge of' a field so that there is some question as to whether it is in or outside of the field, then the same rules as those used in particle counting could be applied to determine Moy, 197$ whether the fiber is in the field ot not. Exa)crimcnlal In order to determine the effic<~cy of the proposed counting procedure a number of asbestos sa111Ples were C:ounlcd using a direct counting method a11d a record was kept or the ni.mbcr of void fields observed. Most probable number data as determined from 120 FILDI COUNTED I '0 .0. !!! ~ or: ... 0 ..& ! rl 0 0. I z ~ 3 c0 Ll to i 0... .!..!.! :ce zo Iw ~ 1.1 ,; w ; 1.4 z::> w 1.1 .aI-D' 10 ,_ o.a ~ 11 o. 0.4 0.1 IZO FIELDS COUNTED) .,_.,,..~4 CONr UNC[ INT1t\M. A-IIOIECT COUIIT Q 0 0 o oa o o o t.o 1.2 1.0 DIRECT COUNT, FIBERS rEI! FIELD Figure 2. Most prohahlc number data 11!1 deter min~'tl hom Equation 6 vcnu11 direct count. 0I OIR(CT COUNT1 f"IBERS JIR fiELD Figure 3. Plot of most probable number venus direct count for data from computer simulation for ..20 fields. 1100 FIELDS COUNTED! 0.. !ol ...~ cw .e \; .; .I z ~ "..0 0: ..to 0 -----=~~,-==-=- ---------- --------.., 0 II I DIRECT COUNT, rl81111 P[lt f"l4.1 Figure 4. Plot of most probable' number versus direct count for dnt11 from computer simulation for too field!!. FMSI 05135 .... Amc;im11 /mlll.fll"iliiii.I'J:il'm A.uociulimr lmmwl Equation 6 arc plollcu ils a function of the direct count which was observed for the samples and the results arc shown on Figure 2. Also shown on this figure arc the 95% confidence limits for both the MPN method and direct counting. Although there is some spread in the datil, the gcnc~al reproducibility is app~1rent. However, it appears that the most probable number method consistently gives results which arc lower than those determined by direct count. This observation is consistent with a similar one of Chapman's who surmised that the dirferencc could be due to failure to see a single particle in an otherwise void field. For more extensive work a computer simulation was developed in which fields of 10,000 bits were assigned particles randomly corresponding to some preset particle den sit)'. Then field~ of various sizes were randomly chosen arid the average number of particles per field determined using the two methods. In addition, the absolute number of particles per field was determined. From this simulation it was possible to carry out non-biased counts using both conventional counting and the most probable number method for samples of 20, 100 anq 200 11 1100 fiE LOS CQuNTU I .9 .....;;: " "~ i w ~I f i 0I OIIUCT COUNT, "BERS ~U fiELD Figure S. Plot of most probable number versus direct .count for data from computer simulation for 200 fields. 383 fields. These data arc shown in Figures 3, 4 and 5. Unlike the actual cxperimcnt;1l data, however; there appears to be no bias toward the direct count information, indicating that the higher count averages n_otcd on the actual direct counts results from a bias introduced by the observer rather than by the technique. Similar to Figure 2, error limits for the 95% confidence interval arc shown as dotted lines. Ad,mllages and Disadvanh1ges The advantages of the most probable number method are threefold. _Sampling times are shorter, lighter samples with less chance of overlap can be used, and counting times arc shorter. Using fairly light samples for asbestos concentration assessment means that shorter sampling times arc needed in. the field, often ari advantage to the industrial hygienist. For a given number of fibers observed, the MPN method implies greater accuracy if this total number is relatively small. There is Jess eyestrain for the microscopist since he only has to determine whether there is or is not something there, and not re-:- solvc a specific number of fibers. if prob- lems of fiber clumping have occurred they will be more evident because of the lighter sample density. Finally, since fields arc being counted instead of particles, the counting should proceed at a faster pace. For example, in discussing particle counting by the most probable number method, Chapman pointed out that one observer could deter mine particle concentrations about twice as fas~ using the most probable number method compared to standard counting methods. .,whhe another observer was three times as fasJ using the MPN method. We have not 5tudicd counting times objectively, btll sub- je~tivcly the people in this laboratory who have compared the two methods for counting asbestos fibers also feel that the most probable number method is much fi1stcr. The principal disadvantage o! the most probable number method is that it is not -~ . ,_ .i FMS\ 05136 . .. . - 384 rigorous. An observer co~ld," in theory, accurately count the total number of fibers deposited on a filter whereas using the most probable number method, even if the whole filter were assessed, the observer would in the end still only have an estimate of the number of fibers present. In addition, for a given number or particles per field, the 95% confidence intervals for the direct counting method nrc slightly narrower than for the most probable number method, the effect becoming increasingly pronounced when the average number of fibers per field exceeds two. The accuracy is sufficient, however, for routine asbestos counting. Summary A procedure for evaluating asbestos fiber counts is described which uses the most probable number method of bacteria counting. This technique is faster than conventional counting methods, with approximately compariblc accuracies, although it suffers from a lack of rigor and requires the ob- May, 197$ server to estimate fibers to within an order of magnitude before counting. However, for the routine asse!lsn~ent of a large number of asbestos samples this procedure would seem to be more desirable because of the .economy of time as well as being easier on the observer. References J. F..tlwards G. H., and J. R. Lynch: the Method Used by the Public Health Service for Enu: mcration of Asbestos Dust on Membrane Filter.;. A 1111. Occup. 1/yg. 11: (I 968). 2. Joint AIHAACGIU Aerosol Hazards Evalu ation Committee: Recommended Proce,lures for Sampling and Counting Fiben. .Amer. llrd. 1/yg. A.~soc. J. 36:83 (197.5). 3. A1111011.: Occupatio11al Exposur~ to .A.,bestos, p. viii-.5, HSM 72-10267. U.S. Dept. H.E.\y., NIOSH. Washington (1972). 4. McCrady, M. H.: The Numerical Jntcrpreta lion of Fermentation Tube: Results. J. Ill/~.- Di.r. 17:183 (191.5). ~ t:!! : .S. Cochran, W. G.: E!ltimation of Bacterial Den- sities by Means of the Most Probable Num ber. Biometrics 6:10.5 (19.50). 6. Chapman, H. M.: Dust Counting by the Most Probable Number Method .A.M.A. Arcll. In Jrmr. Hyg. 8:234 (19.53). . '. - ........ In -I do v. pc w th en co en dil to. ci4 ht: rc ici tn Stl nl fo th pl be a an m ', ta gr FMSI 05137 -..f. ' \;,. .' . ~- JOURNAl OF PAINT TECHNOLOGY ~ deal.of ~ttEmtion 1; :~ ' and publicity in recent years, , ,? .,i, floor tile'' and in i especially after it was designated a "target health hazard" by OSHA and a compounds. It is used..in.other } "hazardous air pollutant" by the EPA. Many of the articles on asbestos by the press have been emotionally oriented or distorted and, in some cases, stories have been sensationalized, based on obvious misinterpretation of facts. The use of half-truths or unsubstantiated statements has led to general confusion and the unfair castigation of asbestos and products containing asbestos. plastics such as polypropy]ene;poly<t ester, nylon, melamine, ~. ,Sill~ ; ., cone, and vinyl. Asbestos provid9f ,. :~": valuable function in such products as j:;;: The purpose of this paper is to put the matter of asbestos use and asbe~tos hazards into a logical and practical perspective. In this paper, the different types of asbestos and their many uses are discussed, along with go.vernm~nt regulations controlling the use of asbestos..The health hazards associated w1th asbestos, both occupational and environmental, and some industrial ex- perience with air sampling and dust control,m,easur~s,are also covt:tre~.~~ t~- KEY WORDS: ;~ Asbestos; ~ ~ ~ '' Plastics; Air > pollu:'t"i:.o:~An~-.;~"'-"T""~~~x'i.{c-$o;"l':o~-g-"'y~ .t:t~"i":Sci~;l"f'~~:{r'h;i,r:._~l. brake linings, chrtch facings, electrical 4f'; 'ture.' comi>onents, automotive parts; furrii.;::~/ boatS,. sealants; Coatings, adh~,:(' sives. and mastics. The most important .:. functi0!115 of asbestos'bi pluties are re- inforcement, dimensional stability; ""' heat resistance, ftow control, and gen- '; ., " . eral-purpose filling. Most of the fuiic- tions are . 5upplied by'' short-fiber , cbrysotile astbestos fiber," althougb What is Asbestos? longer chrysot:ile fibers and other asinsulation. Although there are some bestos varieties are sometimeS' re- Asbestos is a commercial or generic term used lo describe six naturally occuning "asbestiform" minemls that are fibrous, hydrated metal silicates. The six varieties are divided into two classes-serpentine and amphibole- , deposits of anthophyllite in the U.S., quired fur particular properties: ~ . most cl it is imported from Finland. It is used primarily as a filler for~ polypropylene and in insulating materials.,. A. comparison of the four:;-, Amo?g the .several ~dvaiitages of. :-varieties of asbestos which are of oom-.2:.,:-.. c~sotile, ,which set .It apart .from mercia} unporbmce is presented ~inf>'! the amphibole minemls and account' based on their crystal structure. Chrysotile is the only member of th~ Tal;le 2. It should be noted that there::. for its widespread 8'1ld in~.:us-, are significant differences between age, _are world-wide a~~l.ability, ;ne- serpentine class, while the 11mphiboles indude crocidolite, amosite, anthophyllite, tremolite, and actinolite. chrysotile and amphiboles with regard to chemical composition and certain physical properties. charucal strength, fl_erJbi~ty, p~ve surface charge, low ~n C<?ntent,.sof!ne9S, and low re&active mdex. It IS Chrysotile is by far the most-used J ,, consei'V'Iltive]y estimated that chryso-. , variety and accounts for over 9~ of 'r-where is Asbestos tile asbestos is used in over 3,000 ap- U.S. consumption, as noted in .Table Used and Why? plicatiom-and, in most ofthese appli- 1. cations, it. is an essential ingredient Crocidolite, also known as blue as- Asbestos has served mankind for for which- no replacement is readily bestos, is imported from South Africa. more than 100 years in a broad vari- available. Because of its high mechanical strength and good resistance to acids and alkalis, it is used to reinforce a limited variety of plastics where its pronounced color is not objectionable. Amosite, also imported from South Africa, is used primarily in thermal ety of applications. The general areas in which asbestos is used in the U.S. are shown in Table 3. Based on information from asbestos producers and consumption surveys, it is estimated that the plastics industry uses about 331 of the 800,000 tons consumed an- The information in Table 1 shows that the use. of chrysotile asbestos and its share of the total market are steaaily increasing. This is due partJY to technical advances permitting the inbroader 115e of chrysotile in plastics and the general decline the use of . nually, which makes it the largest asbestos in certain fireproofing and in- p,..,..led a1 the Golden Gate Society's ManalfC'IIIenl Seminar held in San FranciKO, Calif., Ju!'"y.,~~~~.1~~;.. Niapra Falla, N.Y. 14502. single user of asbestos 6ber. The largest uses of asbestos by the plastics industry are in vinyl~amestos sulating materials. In addition, there is increasing evidence that crociclolite ,f'land ' amosH:e--a-re~'m' a%re,._h;a_z:_ard~o-us to VoL. 47, No. 61 I, DECEMBER 1975 'f,~) FMSI 05138 ~. Year 1967 1968 1969 1970 1971 1972 Table 1-Apparent U.S. Consumption of Asbestos, Tons Total :;: . Chrysotile Amosite Crocidolite 14,917 (2.1). Table 3-Apparent U.S. Consumption of Asbestos By General Use Areas , Area of Use Percent of Consumption 1!1,965 (1.7) Construction r 10,558(UI)_' ~ .FI~r d~ 8,9!16 (1.2) Felt paper 6,95!1 (0.9) .. '' ~? :l ::;~t:#p ' .. ':-t~~~-~'". human health than chrYsotile.~ 1970, the me of crocidolite in Britabi . ..,asbes.tos~~:"Another iJnP.ort'lmt . oers of. the IlliematiOn&l Agency for ReseaJcll on:Cancer (a .division of the has been restricted after a panel of : sideration .is the relation betweeri World Health Organimtion): .."'There ca.ncer. 'an meso-'experts "concluded there was suffi- ~ cigarette smoking and lung aS is evidence of associatiori of cient evidence to suggest other types reported by Dr. E. C. Hammond and thelia] tufi:tors with air pollution in of fibre should be substituted for crocidolite wherever possible.",. 11 ''" ,-" ~~~ ~- =:.~ ~~~ ~r:~f-:;~~~~- :y What is the Asbestos Hazard? It is readily aci:epted that ~best~, canlike many other foreign bodies, cause disabling lung damage (pulmonary fibrosis), commonly referred to as asbestosis. This disease and bronchogenic carcinoma (lung cancer) are the two most common asbestos-related diseases. It is important ro note that, based on epidemiologim] data, these diseases. ,have occurred Dr. I. J. Selikoff. In this study, they reported that: "11: seems clear. then, that lung cancer is uncommon among asbestos insulation workers who have ' no hisrory of cigarette smoking and the neighborhood of crocidolite mfues, and of factories using 'UiixtureS. of 8s- ;.> . bestos fiber types. The evi!lenee~je- f excess .lates to conditions of maliy years 'ago. :r~ There is evidence of no risk . that if the risk is increased, such in- of mesotheliomas from asbestos :air creaseisnotgreat.". , :v .. , pollution which bas 'existed:in.the ...' ;~~:A thirifdisease:~mesotbelio~:; has~~: .l_leigb!>~r}_lood 'of. ~I"Y,Sotile~ana.'amo-;~ ' 'mmce more r ~ tJy been ed -1lSSOCla't ,.w tt h>,ti'\0",..si t e mines. There .,, ' are''o~f,rielesdothemliffer- "'/' .; persons exposed :to asbestos. Meso-!': ' ~ "1~- aDd . -~ .. ' : : ; .. wh":hthelioma is an extremely raTe cancer.;" of the lining of the chest' (pleura) Or-;' the abdominal cavity (peritoneum): ~'uses .. of ur . lished. There IS nhoav..eevr.iundoetnbceeaeroenfas-~,~,~riis..k.,c,:?::. In contrast to the1nu g diseases, there,....; t.o..the .g...en::e:r:.a-l<;p ub!4lhicilatc..:present.:';<;.':~.,~..,.~.. "'' primarily in worken; with high, long- , is some evidence that mesothelioma'' The same 'body quOted above bas term exposures to asbestos dust. It is can occur after brief exposures to also concmded that there is, at pres- . of further interest that one noted re- relatively high 6ber levels. ent, no evidence of lung damage by searcher has reported that nefther of these diseases is peculiarly related to According to the 33-member Ad- visory Committee on Asbestos Oan.. asbt!stos to the general public; and. . such evidence as there is does not in- ' iT' droare any risk of cancer resuhing :3!. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - from asbestos Bbers present in.water,';~'> Tabl~ 2-Comparative Data for Asbestos Minerals" beverages, food, or in the Used Formula Chrysotile Crocidolite Amosite ., Anthophyllite for the administration of Composition, .% SiO, MgO FeO Fe,o. 3Mg02Si0.-2H,O Na,OFe,O, 1.5Mg05.5FeO 7Mg08SiOH;O 8510,-H,O 8SiO.-H,O . 37-44 !19-44 0-6 0-5 49-5!1 : . 0-!1 .:' ' ' 49-5!1 '1-7 ':>~nl ..; ; ' 56 58 28=M ')i; '!,,f;: :'~ 1!1-20 :-;:,, ' ' !14-44' :<' .!1-12 _{Y 17-20 -h" edt&;:_ ''~'!:! While there seems agreement' that the pUblic:!$ ,not any present .dangel' kom aibestos;'it . is also recognized that excessive,long- term occupa'llio~ exposure aui eause :c serious health problems. A1so,if lnan- made . emissions -are not con:trollea,: ' AI.O~ tf,O CaO Na,O CaO+Na.o 0-2 : 12-15 2-5 2-9 ~-. 2'.:..:'5 4-8 ; ~; ;..; '0 o.:..::s ~ '- .: '' 0-2 1-6 then environmental OOntamSD9.tion could could approach baimful levels. During the past two years, sigmhnt legislation bas been enaCted by the Federa:l government to reduce and Crystals Color Texture Fine fibers Gray green Soft silky B1ittle fibers Blue Harsh Prismatic Grayjbrown Harsh Prismatic Gray Harsh control occupational exposure to as- bestos Sbers and to minimbe fiber emissions to the environment... Addi- Flexibility Hanlness, mohs Fiber diameter, A Tensile, mpsi Very good .2.5'4 JBO,liOO 800 Good 4 600-900 600 Good 5.5-6 600-900 200 Poor 5.5-6 600-900 <4 tional smndards or regulations have been proposed or enacted by many states and local governments. : . ;.; l >. .<,)~-~ f!nt;..rttJ+:t~ ~~-L~ ~i ,J;;~f' Surface charge Resistance to acid Resistance to alkali Positive Poor Good Negative Good Good Negative Good Fair Negatil'e Very good __Good,"'- Summary of OSHA Regulations \' ;:. > ' F< 0: ~ ' ,, ' '! The William-Steiger Occupational Chern. ,:r:,h.:"(a) Sourcrs: Madrm Plallia Encyclopedia (1975), and Encyclopedia of V~J.' 2. Salety and Health Act of 1970 became effective on April 28, 1971, with FMSI 05139 joURNAL OF PAINT TECHNOLOGY ,,. the following Congressional purpose: Improper interpretation of the reg- EPA Standards "To .assure so far as poss~ble every ulations has created many miscon- working man and woman jn the na- ceptions about equipment and pro- lion safe and healthful working con- c~dures needed to properly use ditions and to preserve our human asbestos. If exposure limi'ts are not resources." The Act established the exceeded, there are no further' com- Occupational Safety and Health Ad- pliance , requirements except for med- . eiamina-ministration (OSHA) within the De- ical examinations. Medical arepartment of Labor, which has re- ,, . tions required' for all... ,. " sponsihiJity for administration and ':'""''in any~pation exposed enforcement. Research and , : " concentratio~,of asbestos Whereas OSHA is responsible for trhe protection of the worker, the En- en-vironmental Protection Agency (EPA) is charged with improving the vironment to which the .general public . is_ exposed. On March 31, 1971, U.: be6tos, . -along with <beryllium . mercu'J&,was . .,, ~" functions a-re handled by the .ut::uar'l- ment of Health, Education" fare (HEW) through the Institute of Occupational Safety and Heahh (NIOSH). Five million em- ployers and 60 million of the nations 80 mi1lion workers are covered by OSHA. Specifi-cally excluded from coverage are government employees and operations which are pro'tecred under other federal health and safety. lam>. In a news release issued January 4, 1972, OSHA announced a Thrget Health Hazards Program aimed at improving health iiactors associated arewith working condftions. The follow- ing five substances were designated to be the focus of iniool and con- certed efforts by OSHA and NIOSH: asbestos, oot'ton dust, silica, lead, and carbon monoxide: : :, . . -~~ . tern~~~~.. . 66, April_6, 1973."'4 cloltbinig , AlthoUgh no numerical emission'.st&il- are required in the construction trade) ' dards . )veie establishea;~~Cri- for the spmy applkation of insulation A terii'are :Prescribed: to, prevent't or>~ and fireproofing material6, and forthe limit asbestos ~s~ to ~t--~s;, r~moval of. ~ materia~. This spe- side air from asbestos mills,~roa~ay5, <~~. c1al protection 1s not reqmTed for 'lliiY. certain manuliacturing .operationS, ~~h~r use of asbestos u~I~ exposure building demolition, and the spray-on lm1ts are exceeded. This IS also true application of materials used to in- . for :other items such as specially sulate or fireproof equipment and eqmpp~d t~ols, change ~ms, clothes machinery. The law further requires. laundenng, ~and _waste disposal. Res~tor:~. not a. 5Ubsti~ for engmeenng controls, but ~e ]a~ allows ~heir use whiM; contro.Is .. ~ .. b~ng that spray-on materials used to in" sulate or fireproof buildings, struc- ..... tures, pipes, and conduits shall mn-' tain less t<han 1$ asbeStos on a dry- Implemented, m speaal sn_ua:tions weight basis. This should significantly where co~trols are n.ot feasible .or reduce emissi~~,.!o,~hich the gen- adequate, m emergenCies, and for m- era] public may be exposed, especially frequent short-tenn_ job assignments. in large UJ'ban areas. ~:; .",.; ;- . . At the present time, new standards Caution ~~Is are required on prOd- ::'. . .. the Adminrstrato; ,(of EPA) have been esta:b&hed only for ubes- ucts con'tammg aSbestos e~t where has determined thalt, in order to pro- tos, although, of the 8,000 toxic substances on the NIOSH list, only 500 the ~hers have been modified .by a bondmg agent or other matenal to vide an ample margin of safety to protect the public health from as- are covered by standards and many prevent dusting during any normal bestos, it is necessary to control emis- of those need updating. The new suibsequent use or handling. Besides sions from major m'an-made sources Standard for Exposure to A11bestos mw asbestos fiber, produc'ts which crf aSibesros :emissions into the atmos- Dust was published in the Federal require pacl<iage .labeling could in- phere, -but that it is. not necesslllY to Register, Vol 37, No. llO, on June 7, elude: dry acoustical spmy products proMbit all emissions. ;.,;f?i ,;!Ji;.;;i\;;J 1972. The basic E:J[pOSUre standard is ~nd joint cements, unsaturated roof~ . "In this determination; the Adffiki~ ":J. an 8-hr time weighted average repc;rt(TWA) of five fi.bers, longer than 5 mg felt and . textiles, and some.. in- . sulating proaucts made Without ade- istrator bas Aoadem)'. of rSecliieendce os~n the National ,:w on :as-'i<J:i micrometers, per Cll'bic centimeter of air. The TWA limit ,fs to be reduced quare binders. The labeling of ia prod- . bestos, which concludes.: "ASbestos is~,,, uct does not prohibit j~ ..use. It too important in our technology'ana;~;!' to two fibers per rubic centimeter on should be noted here that m at least economy for its essentia'l use to be:+"\/. July 1, 1976. A peak concentration 9M; of the products containing as- stopped. But, because of the known ' of 10 fibers per cu'bic centimeter is bestos. the fibers are solidly loclc:ed serious effects of uncontrolled inha- not to be exceeded at any time. A]] into .the product therdJy presen:ting lation of asbestos minerals in indus- of the fiber concentrations are those ~ittle danger crf dust generation dur- try. and uncertainty as to the S'hape to which an employee may :be ex- mg nonnal use and handling of the and character of the dose-response posed without protective clothing and product.~ curve in man, it would bt highly im- equipment. The Sm: basi"C require- ment of the new standard is monitor- ing to determine whether or not fiber concentrations are in ex<JeSS of the exposure limits. Some asbestos suppliers provide a monitoring service to customers, and a 'Similar service may JOHN L. MYERS, Marketing Manager for the Calidria A_sbestos Group in Union Carbide's Metals Div., received h1s. B.S: D~gree in qh!lmical Engineering from Purdue be obtained f,rom stare health department officials, insurance carriers, or :private consultants. The law requires that monitoring be repeated as nec- Un1vers1ty he served m in 1951. Jommg Union the Nuclear Division Cuanrtbil1id9e6t6hawt shaemn eheyebaer~ came a Research Engineer in the asbestos group. He was promoted to his present position in 1970. . . essary to ensure that employees are not exposed ro le~Js in excess of the \-' exposure limits. VoL. 47, No. 6ll, DECEMBER 1975 FMSI 05140 prudent to permit additional contamination of the public environment with ashe9tos. Continued use -at minimal risk to the public requires that the major sources of man-!ll1lde asbestos emission inro the atmosphere be defined and controlled.' Dust-Control Measures ! The Asobestos Inf'o111natioll AS:SOOI&" :;: tion/North America reports that. during tne past 30 years, the asbestos industry has spent millions of dollars tu improve mining, milling, and manufacturing methods. The establishment of safer working conditions has been a prime target and this work continues unabated and in close association with government agencies and independent medical researchers.. 'n;. '? The ultimate goals c:6. the asbestos industry are: Reduction of work-area dust to minimum 'levels; Protection . of workers from ~sbestos-related diseases; Maintenance of environmental emissions at levels low -enough to preclude public endangerment: Air Sampling . In order to comply with OSHA standards and to detenlRine the need for dust control measures, air monitoring should be conducted in areas where asbestos is regularly handled or used. OSHA standards require that "all determinations of airborne concentrat:ons of asbestos &hers shall be made by the membrane filter method at 400-450X (magnification) (4 millimeter objective) with phase contrast illumination.""0 The equipment for collecting air samples costs less than $400 and is readily available. A phase contrast microscope .can be obtained for as little as $600, or an eximng microS>OOpe can be modified for "counting" the astbestos fibers in compliance with NIOSH criteria.11 Air samples bave been collected and analyzed on a regular basis by the asbe9tos industry for years. Except for a few applications where dust control is an engineering problem, industry is finding that dust levels are already within acceptable standards or that minimum changes are necessary to achieve compliance. Although data on m1lny asbestos/plastic applicati-ons are not available, the summary in Table 4 is typical of our measurements of dust levels durin~~: asbestos handlin~t in various types of plants and operations. The dust levels reported are ceiling concentrations, and it should be noted that the aDow- handling, .arid aut:om:atic Unusual innovations int~utde: letized asbestos; "special packagin. and treated products; ,,, ' : :-:-;,/ Only short-fiber~ CJuYsoti e able OSHA level is 10 fibers/cc. In able as pellets, but this product serv' ,,, . most ca-ses, the TWA exposure lev.el .;. . a fair portion of the aS-bestos markeLl:~ ~. would he well below OSHA ~but~~<' ;Pellets riot only reduce dust during ,,.;:. dards. Most of the data were.COII~edJ~fecmvtmtional handling but they are ' . before the installation of any special ; :31s0 aVailable in bulk hopper oars and;.~i 'r;dust~control measures.. MonitO'ring ' "";y. ean be transferred and used in totally}'\. teri' shows that obViously dustf oo~:~~:: enclosed systeii'ls Barring leaks in the. .ditions' lire. caused by materials "other-t:c 'system, dust iri work areas is virtuallY,,';~; than asbestos. This does not preclude ' eliminated. Used.;,ln> bulk,. asbestos.:-:.7. the need for' Controls, but. it .rould . pellets .alSo reduce.:. shipping !COsts,':~';:. change their -scope and facilitate rom~ eliminate :warehOuse\ storage':a.nd .;:_. pliance with goverrurient regulations. handling, facilitate automation, reduce <";; .~. Because of "bad press~ ubestos is clean-up, and eliminate bag ,handling>..;:'::: frequently ordered out of use withOut and disposal. The pellets .contain no .y_~-.: regard to whether or not a hamrd binder an<i_are _fpabJ~. eJ!Ougb to be,;.<,: actually exists due to air rontamiDa:. dispersed in_ dryJorm, odn aqueous tion... If accepta!ble dust levels are ... or resinous' systems with;_conventional ;;;,~& feasible, there is no need to replace asbestos at the expense of product high-shear Several grinding types of equipment.~ "'.r-01 . special packagipg 7~ :i;; "T:: . quality or economic penalty. Gordon are currently availalble, and suppliers , Everett of EPA points out bhat in- consider customer requests for unus- fonnation on the biological effects of ual requirements. The floor tile indus; ... asbestos i-s very limited and bhat the try can obtain asbestos in plastic ,bags~-:fr~, effects of many substitutes have not whiCh oan be added directly to..th!: .~ ,:;w.; been investigated at all. Before as- Cl')mpounding operati?n. Asbestos ;in"~;; bestos is replaced, it should be cer- bleached paper. bags ass~l~:;witb .'/: tain that a safer 1lltematiye is avail- water-soluble glue :..anCJ print~ ,with ~'7 canable.~ ,.t''" '~:' 'Jftlltt;.;,?fi~S~~~:~.. . .water-dispersible ~iDk: :be :added d.;":; <"f.Obviously tli~ are'~niore, people exposed to products containing ames- \. .a;cdioru~csttJiycatlotilpeafpoermr7Un;lhaltcioinngs:.;:Bnishes': ..;$, tos than there are to mw asbestos Although ."wetted asbeStos ts not L< ... fibers. As noted previously, more than generally . available, most .suppli~rs, ; 9!n of the asbestos used in this coun- are working with customers to pro:c,,:?:::.. try is in products in which the ashes- vide "dustless" products...When justi->" :... tos is "locked in m hound wit>h ce- fled .by market demand, .aS'bestos cari ment, plastics, or other hinders, so be treated with water, mineral spirits:: that there is no release, or at least no glycol, or other !ll1lterials compatible signifloant relea-se, of fibers in work areas or to the environment. Materials or products with locked-in fibers would include: floor tile, polyester resins. phenolics, sealants, coatings, brake linings, friction meterials, rubber, roofing compounds, and reinfurced plastics. Since an abrading action on some of these products could release asbestos fibers, appropriate monitoring and/or control meastires should be instituted if it is thought that such action woUld release fibers. with the application or system:. ~.; J!*'"t.: Conclusion .. : ! '' / ', ' ... ~ ,~; ' Asbestos is one o~. industry s many raw materials wnich involves a po- care.tentia] hamrd when. not used with reasonable respect -and Although all forms Of asbestos are recognized as hazardous to health when inhaled excessively, there is growing evidence that crocidoJite and amosite are more hazardous !>han chrysotile. Fortunate- FMSl 05141 joURNAL OF P.AINT TECHNOLOGY ..-11' ; ly, the plastics industry uses primarily chrysotile asbestos and, in most prod- ucts, the nbers are locked-in to pre- vent airborne contamination. Al- though asbestos dust levels are gen- erally lower than expected, industry timecontinues to ~end large amounts of and money to further iml:>rmre the of t:he 'workpllaoe~o#J the 88Det:ai Public: is are rieiiq~~.c~)~OO~;j0 pational viroumenml~~~rliaLijmL~t~~ <llrysotile asbestos is 'lln imt>ort:llnt and necessary raw 'I.THlterial. vital to the nation's safety and economy; and, with proper control, it can be used saf~ly and in compliance with govern- .:; ment regulations. Medical, scientiflC:/,rf' .f 0 government, and industrial personnel. 4~~' must continue to work closely to::';"* ;. gether to establish reasonable sure limits, provide safe work and eliminate any possibility of endangerment. .0 . '},~;t:~~~t'-. ' >: . References - ;. 3 ~.-'0~. --. (I) Enterline, P. E. and Henderson, V.; Arch. Environ. Ht:tJlth, 27, 512 (Nov. 1975) . :... . :; : .."0 o . (2) Wagner, J. C., Ann. .Occup. Hyg. 15, 61 (1972). 0 0 :, ::"~ it ' 0 " (!I) Wright, G. W., statement before U.S. Dept. of Labor, Occupational : Safety and Health hearing on pro- posed occupational asbestos stan '. dard, March 16, 1972. p. !1. . c (4) Hammond E. C. and Seh"kolf, 1.' "Relation Of Cigarette SIIIOking Risk of Death of Asbestos-Associ ated Disease among Insulation Workers in the U.S.A.," presented at meeting of the Working Group to Assess Biological Effects of As bestos, International Agency for Re search on Cancer. Lyon, France (Oct. 4, 1972). (5) 'Report of the Advisory Committee on Asbestos Cancers," Brit. ]. In- dustf'. Med., 30, 180 (197!1) (6) "Asbestos," NtJtitnl4l Sajety (Oct. 9, 197!1) ''.io >,.Co'.:;; 0, (I) "National Emission Standards for Hazardous Air Pollutants," Fedef'tJl Rt:gistt:f', JB, No. 66, 8820 (April 6, , . 1975).. . -: (8) "Protecting the Asbestos Worker,". Booklet No. 101D!17, The Asbestos Information Association/North America, p 5. (9) Selikoff, I. J., Industf'. Medicine, 39, No. 4, 21 (April 1!170) (10) "Standard for Exposure to Asbestos Dust," Fedt:f'tJl Registt:f', 37, No. llO, ll!l20 Qune 7, 1972). (ll) Bayer, S. G., et al, "Equipment and Procedures for Mounting Milli!"'re Filters and Counting Asbestos Fabres by Phase-Contrast Microsmpy," Bureau of Occup. Safety and Health, U.S. Dept. of Health, Edu cation, lc Welfare (Feb. 1969) (12) "Asbestos Health Question Per- plexes Experts," Chem. Eng. News, 18 (Dec. 10, 1975). ' (1!1) M~rs. J. L., "Calidria Asbestos Pd lets,'' ASBESTOS (Oct. 1971). FMSI 05142 -~,....,~'~",~, . A;-7~::f~i.St~4!~~~ ~sbes\os Information Association North America 1660 L Street, N. VoL. 47, No. 611, DECEMBDl 1975 Washington, D. C.. .....---tr.d ~-. ..lt:.,. ;r.. . ' tI ~ I ;-. . Physical Parameters of Airhornc Asbestos Fibres in Various Work Environments-Preliminary. Findings G. W. GIBBS and C. Y. HWANG j Dl'parlmrlll 11/ Epitlcmiolu~:.\' mrclllcllltll. !lf'(iifl llr~i.-crsil_\'. 3775 Ullitrr.Jity .~trrrl, Mci111rrul. l'rut'illtr 11/ Q11rhc-c. Cu11uda ..... The results of a pilot inestieation to describe the ph' sical par..meters, lcns:th. asped ratio, rna'"" and !>hupc of airhnme fihre~ in a .-ariel,. of industri&.'S produdn!! proct!'-~ ini:" and handling chr~ '"tile. amosite and crnciclolitc are dc<ierihed. Sumples of air __ .;::f.~ ... borne du.st "en: collected un nudcopure mcmhnmc filters and C"-amined h~ scamlinl! .-. -~---' ;-. '...~,. electron microscopJ. The diameters and h~neth.o; of a~irhnn1e fibres collected durin!! ' :". the dumpinl! of ra" amu,ite at an llshestos produtts 'jtlant "ere l!reater than tho.o;e of fibres collected durin~: the application of amJ!;ite insulation. Chrysotile fihres collect&.'CI in the c:ardinl! area of an a."'be,1os texiile plant al,o;n tendt.'CI to lune smaller diameter.o~ ,. than fibres collected in the dr,cr and bag~:in~: area.o; of an u.'ibestM mill. l'be mca.o;ure- ment'i of fibre dimemiom; indicate that the de~ree of protection afforded a "orker by optical counts usin~: the memhnal\e filter technique j_, likel' tu depc:nd on variety of a'ihestos and sta~te of proceo;~in.:. Preliminan l't!'iull'i arc not in <"nnflid "ith experi~ mental data su~r;:e~linr;: that a~heslosi" might he related to the ma..-... of airhorne dllht and rima mali~:mmt mesothelial tunmro, to ex O!illl'c tn fibres in a . cific nan e of abre diameter amd t~ugth. ~. .t i . ..1 ~..! '- ALTHOUGH ALL COMMERCIAL VARIETIES OF ao;b\!stos hav.: been shown to produce m..:suthelnmas wh.:n inoculated intra-plcurally into rats. primary malignant mL"Sothclial tumours do not appear to occur with equal frequency among men working with asbestos {Table I). There is some indication that the prevalence of radiolog~cal changes (asbestosis) and lung cancer mortal~ ity also vary with occupatiori.~-:u.u These differences in health experience might be explained by difkrcnces in fibre type and the quality and quantity of exposure. Epi- demiological investigations in sen:ral occu- pational grnups indicate thm radiological changes and lung cancer an: rdatcd tu level uf cxposure.:;_:.- 11 Smoking ap~'k.'ars to be an additional factor which complicat~s th~ asbL-stos lung ~anc.:r relationship.'~ The rclalinnship h'-twc~n primary malign;uu lll\."SU- thclial tumnurs and lc\'ds tlf '-'"l"lsur'- arc ntll dear and it seems prnh<~hk .that sumc uthcr (actur or facturs must be sought in order to explain -the un'--vcn distribution nf this tumour among occup;ttional groups. The ability of a fibre to initiate a dis~usc process in the lung or on the pleura depends un its Jl')Octration. deposition. retention. and hiologieal activity. These depend ma;nly on the physical characteristics of the fibre. First. the settling velocity of a fibre depends on its actual diameter.n and explains why fibres as long ~ 200 flm arc sometimes round in lung at autopsy. Second. straight ribrcs arc mor!! likdy to penetrate deeper into the respiratory airways tban curly fi- bres.H Third. uiamch:r anu length might both "be import;mt in the ability or asbestos and other fibres to induce mesothelial tumuurs.n.u; These physical p~ramctcrs of airbnrne fibres in the worl cn\irunment have .not been l"re\'inusl~ repurtcd. The possibility that the t.:h;r;M:tcristics uf ;tshL"Shls fibres such ;~s di:und~r ;mu shape might ch;:ngc during proc- essing prompted a pilot investigation to determine the physical parameters nr air- 459 .. r.--., , r~-.~. Yl'f.- ~ .. .._..,, ' ., '.. : :~..~ . """:"'"'"..,t,~ .I FMSI 05143 J -~ .I :-~ .I l J~1 :t' ~~ l- I ....... . .t. \ .... -, .' -~ ~ -: .. l _f . i-- '- ...-. ..,~ 4 . .:. I... I ~ tt ..JI.. I. I .I -.I f . ..,. I .i. .. :! . ~- .\ ~ -~ .. .:;.. I ! .. .~ . . .I ........ . _. ~ I. . l'. .. .- .: .1 .. ',:_: t' .'" f'.,. ~ -. f'l' '. \ :.;,t . ~ .. . ~ -~ J , TABLE I Primart Malignant Mewthelial Tumours Reported in Studies of Various Occupational Groups. ~ Study Group Total Deaths Insulation Workers (USA) (mixed exposures) Scliltofht al (1969)2 380 Qrysotilo Miners and Millers (Canada) Mc:Donald et al ( l97f>3 3,270 Anthophyllite Mining (Finland) Meurman et al ( 1972)" .. 248 Asbestos Textile Industry (UK) (mixed exposures) Newhouse (1969)5 436 Croc:idolitc Mining (S. Afric:a) Webster (1972)8 Jurr~. 1915 No. Mesothelioma .21 5 . 20 88 '~ j t.! - 1 .i.. 4 i I -. ;J Amosite Mining (S. Africa) Webster (1972)8 ~.. . Amositi: Factory (USA) Scliltoff ( 1972)7 borne asbestos fibres. to which 'WOrkers in lOS 5 of .Two samples airborne .dust were ex- 'Z' '"( f. I L1 different occupations are probably exposed. amined from each location. Methods Preparation of Samples for Analysis Conventionally submicron airborne asheS- tos fibres have be>=n exhmined by transmis7 sion electron microscopy. This has involved considerable handling of the dust samples and the original fibre diameter distributions in the samples may have been altered in the process. In .this study, samples were exam~ by scanning electron.microscopy. which required much less laboratory manipulation. Samples of airborne asbestos dust were collected at the following locations using nucleopore membrane filters (G.E. 40, .37 _ mm diameter, pore size 0.4 pm): .......... . (1) at the carding machine in an asbestos textile plant which used chrysotile only. (2) at an asbestos products planl during the emptying of bags of amosite and crocidolite'into hoppers "dumping... (3) at a local oil refinery during the ap- . plication of insulation materials containing mainly amosite. - (4) in th~ dryer and bagging areas .of a chtySOtile mill. A circular portion of the nucleopore filter was coated with 150 A layer of gold-palladium (60-40) and examined on a stereoscan electron microscope (SEM) type . 96113 Mark 2A. Scans were performed across the diameter of the filter beginning at the centre of the original filter which was on circumference of the mount. High resolution electron photomicrographs of the fibres in ran- dom fields were taken. TPe magnifiCations on the SEM were identical to those used by Timbrel)l7 for the measurement of fibres using transmission electron microscopy. i.e. 2,500x for. amosite. an~ 6.000x for crocidolite. We also used 6,- 000x for chrysotilc_. Measurements were made from photographs using a magnified scale and for each fibre we measured: (1) ~e diameter (d,)--(the width of the central portion of a fibre excluding particles attached to the fibre). (2) coil diameter (d,..)--(the maximum fi- bre diameter including attached part_icles or widest diameter ofcoil) I ~i .... . "1 A. ~1 .a(..... l ~ J 1 ' ! ., i.. i- .:~ l f j ....1 t 1 \o" j ' :i .1 .. !,.-,...;,. fMSl 05144 .: . ..- ~-...--' ~' . ':l . j I , .,,...., I. Amrrican Industrial Hygitmr Association Jo11rnol t' (3) coil length (lc)-(the length of the fibre as it appeared on the filter) (4) true length (1,)-(thc length o'8 fibre after straightening) {5) coil-aspect ratio (L:!d.:)-(the ratio of coil length to coil diameter) (6) aspect-ratio (lt/d,)-(the true length to true diameter ratio) (7) mass (m)-calculated from the true fibre diameter and stretched fibre length by assuming that all fibres have a circular crosssection. This assumption was not strictly valid for amosite in which it is rectangular but was a close approximation for crocidolite in which it is eliptical or circular and for c~ry50tile which in cross-section has a swiss roll appearance. As the way in which amosite fibres would be orientated on the filter was not known. it was probably reasonable to use a circular cross-sectional area for calculation of average mass. The densities used in the calculation of mass were 3.45 g/cc for amosite. 3.37 g/c:: for crocidolite :md 2..S5 g/cc for chrysotile. Measurements of the parameters of fibres taken from various regions of the filter showed that the distribution was reasonably uniform. Results The ranges and median diameters, lengths. mass and aspect ratios of airborne asbestos ... .. n: ;: ;.rl".. . ~\-~ ~ ..~.. i~~~ . . _.("LJi~.:. ~.:._ . , 461 fibres by fibre type and pro_cess are sum-. marized in Table 11. T..Ue Fibre Diameter (dt) -The median diameter of amosite fibres during the emptying of bags (dumping) or rctw am~ite at the asbestos products plant (0.41 S p.m) was greater than during applicationof amosite insulation (0.370 flm). but the range was almost the same. The minimum diameter of the fibres was slightly Jess than reported by Timbrell et al11l (0.098 flm). Cumulative frequency distributions showed a tendency for airborne amosite to be finer during the application of insulation. The median true fibre diameter for croci. dolite during dumping was 0.248 fLm (range 0.011 to 1.347 flm), which was less than for the amosite fibres (Table II), collected during the application of 'irisulation. The presence of fibres with diameters as small as 0.0 I p.m.indicated that a small amount of chrysotile may have contaminated the sample; a:nosit-e and chryso!i!: were a.!so c:oed at this plant. The modal diameter d,r crocidolite was 0.25 p.m which was greater than the peak reported for the UICC standard reference samples of crocidolite by Timbrell et al (0.16 flm).'8 Tnis difference m'ay . be related to the source of the._fibre and methods of treatment before measurement. F:or chrysotilc. the median diameter was 0.17 flm in the dryer. 0.16 flm in the bag- TABLEJI .;_ Physical Parameters of Asbestos Fibres ..:; ! Amosite median d, (~&m) 0.4 15 11 (~m) 3.90 d (,.m) 0 0.510 /d lr {~m") Mass ( x JO"l:! gm) Aspect ratio, ~ 3.60 2.200 s.oo r Dumping range 0.072-2.922 0.57-38.04 0.072-3.00 0.57-311.04 0.011-251.271! 3.06-.50.16 ' Amosite medi\IJl 0.370 2.~0 0.428 2.93" 1.000 7.20 ~ Application Crocidolite Dumpinl! Chrysotile ran~e 0.071-2.482 median 0.248 ranl!e 0.011-U..t7 median 0.173 0.47-30.94 2.50 0.17-16.1S 1.25 0.075-3.36 0.292 0.05 1-1.347 0.317 0.47-33.39 2.49 0.17-16.18 1.18 0.006-1:!6.033 0 ..538 0.0001- 3K.714 0.126 3.10-.50.81 9.65 3.22-.56.18 6.30 .-. Drying range 0.011-1.446 0.:!:!-14.88 0.05:! :!.::!65 0.2::!-] 6.12 0.001::!~ 25.866 3.07-64.41 Chrysotile median tUSK 1.35 O.:!M 1.24 0.12tl 7.2.5 t Baginl! range 0.013-1.135 0.34~ 9.KI 0.013-1.551 0.27-15.01 0.0017- 23.011 3.07~36.76 Chrysotile median 0.150 1.00 0.233 0.93 0.068 6.60. _ -1.. .~ ~. I r--:: Carding ~..:.,. _,. ~ \ .1......... -- range 0.011 1.:!51 0.26-12.2-l 0.011- 1.829 0.23-12.16 0.0001- 15.432 3.~81.95 .~.. FMSI 05145 ..... ............,_ .. -,............~ .... .I .... .II )" -.l.. 1 .I r ~ j. ..~a;.t,. ;.h-,1 4 ... .-JiLl :_!!,:,;..,:I :.;. ~ ~,0,..' ~...:: ..... ...... lune, 197S ging area and 0.15 p.m during carding. The perccntag~ of fibres less or.. equal to 0.5 Coil lengths also decreased from dryer to carding operations. p.m in diameter wa.o; 67, 82, and 88 respec- tively in the dryer, bagging and carding .areas. Aspect Ratios (lddt) Aspect ratios for amosite ranged from Coil Diameter (de) 3.1 to 50.2; fibres were defined as having a . length to diameter ratio of 3: 1. The median There were 3.3 per cent of airborne fibres . f ratio for airborne amosite collected in the collected during the dumping of amosite and manufacturing plant was 8.0 and for that 0.5 per cent during the application of amosite insulation which were classified as not collected during the application of insula.;. wastion 7.2. The median aspeCt ratio .for straight. These deviations from straightness croc!dolite was 9.7, which was slightly gr~at were due mainly to the irregular margins of fibres resulting from attached particles. The er than for amosite, although ranges were similar. Although there were differences in -coil diameters of amosite were larger than the true diameters (Table II). Crocidolite fibres were generally straight and their median .coil diameter only very slightly larger than the median true diameter. ln contrast, cbrysotile fibres had narrower coil diameters at the later. stages of processing. the ranges and median aspect ratios (It/d.) of fibres collected in the dryer. bagging and carding areas (Table II), the median coil aspect ratios in the dryer, bagging area. and textile plant were similar, 4.4, 5.0, .4.4 respectively. Eight per cent of fibres collected at the True Fibre Length Ot) dryer, 9 per cent of fibres collected during bagging and 12 per cent of all chrysotile fi- As there were few "curly" amosite fibres, , bres collected during carding were consid- tbe median true or stretched length!! were ered to be ctrly (i.e. not stmi~ht). virtuaiy identical to ..coil lengths". The true lengths of fibres ranged from 0.57 p.m to Mass 38.04 p.m (median 3.90 ,..un) in the manufacturing plant and from 0.47 I'm to 30.94 p.m (median 2.50 JLm) during the application of insulation. A cumulative frequency The range and median mass of the variour fibre types by process are shown in Table II. distribution showed that insulation workers were exposed to shorter fibres. Crocidolite fibres during dumping ranged in length from 0.17 I'm to 16.18 I'm with a median length of 2.50 p.m. ILength-diameter Matrices _ Recently gested that efix~preersimwei.nthtaldieavmideetenrcse hac; less sug~ than _0.5 p.m and w1th lengths greater than 5 p.m The median true lengths of chrysotilc fi- to 10 p.m might be responsible forthe pro- bres collected in the dryer, bagging and card- duction of mesothelial tumours.a Length- ing areas were 1.25 p.m (range 0.22-14.88), diameter matrices for.airbome amosite, cro- 1.25 JLffi (range 0.34-9.81) and 1.0 11m cidiolitc and chrysotile fibres arc shown in (rangct 0.26-1 2.24) respectively. The distri- Fi!,!ure 1. butions of fibre lengths showed that fibres The percentages .of fibres with diameters in the dryer area were longer than elsewhere. less than 0.5 JLm and of lenA,'lh greater than The percentages of fibres with lengths great- . 5 p.m during the ha-ndling of raw amosite er than 5 p.m in the dryer samples were 11.1 and during the application of insulation were in the bagging area 4.8, and in the carding 17.0 and 18.3 respectively. The results for areas. 2.3. crocidolite were very similar to the results - ~ ' ; ...1i ."! ''li:i "I' 1 --- l i tI 'i ~ \ i ; ., J "~.I, .. .. ' ., I r ll r- ~m :t :'lf1 . . ~~ !: .~ , .,\, ' I '41/'ot - T..piir-:::,' .._,..:.-....,.:. : FMSI 05146 '.. " .. ...~ ... I . .-.; ;. :c . . . I. .., ~ h ;.: .:. ..... ' ., I .I 1( '. : ~. .::J: ~; t .' i I ! I Am~rican Industrial Hygi~nt Association Journa,l .j-ot-te" (o.s,. >01-ter o.so,...~ I4o ((.o zs .11111 l, ,to.tr.-o.s ,1111) (o.st-o.7~ .11111 ~--== (0.71-l.o ,.) . fi)t.o ...; 4~ 3n.,_ 1fh_ BLrL J[L [L ~r::C'l 1[L_ [6__ ~ " 0 5.0 10.0 0 5.0 IO.D D 5.0 10.0 2.5 7.5 2.5 7.5 2.5 7.S 0 s.o 10.0 2.5 7.5 i lII I 0z.s5.07.510.0 1-et".'P"l Figure 1. 'Length and diameter di!>tributions of fibres collected during various aiibestos processes. for ~osite with 17.5% of fibres in this size range. The percentages of chrysotile fibres in the dryer, bagging, and carding areas with coil diameters less than 0.5 1-1-m and coil lengths greater than 5 1-1-m, were 1.45, 1.0 and 0.4 respectively. The propOrtion of fibres with these dimensions decreased from the dryer through to the carding operation, but the number of fibres examined was too smaU for differences to be reliably assessed. When true lengths and true diameters of chrysotile were considered the percentage of fibres greater than 5 1-1-m in length aml less than 0.5 1-1-m in diameter measured on two samples of dust from each area was 4.7 and 8.0 per cent at the dryer and 2.8 and 3.4 per cent in the bagging area and 1.1 and 2.0 per cent in the carding area. This trend was similar to.that shown by-the coil lengths and coil diameters: : ..._.... . The total fibre concentrations in the vari-~ ous areas studied were quite varied. being generally highest in the carding area. Submicron Diam~ter Fibres . If we assume that the optical count or fi- bres by membrane filter technique is limited to fibres more than 0.5 1-1-m diameter and more than 5 p.m length. the percentage of the total fibre count that would be observed by optical. methods is shown in Table Ill. Considerably more amosite fibres would be observed optically than chrysotilc or crocidolite. Discussion This .pilot investigation shOwed that dif- ferences in the physical parameters of air- horne fibres at various stages of processing . could be dete.cted. Althou~h ~ the number of samples examined was small and the results ...... i ~- FMSI 05147 l ; .I ~ i ] I I i .'j . ; ,.~ -i . t J .,c.. f :'i ~f- 4 , t 't 1l. }.. r l 1 4 f 1 t .~ ; ~ l 1 i .1 -..~ II '{ .. I . ~. ' I i . .. .... -~ I f' . 'J - L. { TABLEifi Percentage of Fibres Greater than 0..5 ,.m Diameter and .s,.m Length ; Operation Percenta1e of total fibres of diameters >O.S ,.m diameter and lellath >.5 ,an Dumping amosite Applying amosite insulation Dumpina croc:idolite Drying chrysolite Baaling chrysotil: asbestOs Carding chrysotilc in a textile plant ... -- .....~. 27~ 13fj(, . 41(, - IOfJ, 2.19(, . - June, 1915 require confirmation, certain observations were worthy of note ... (1) The number of fibres visible by optical microscopy depends on the fibre type. In the control of asbestos exposure and in the investigation of dose-response relationships these diffc:rences could be important. Counts would tend to be underestimated when fibre diameters were fine, and, hence, more respirable. Existing en.r:ironment&l standards take no account of this. (2) Amosite fibres tended to decrease in diameter from the raw amosite dumping stage to the application of insulation stage while the lengths of fibres were distinctly less in airborne dust ~ollected during the application of amosite insulation. Chrysotile fibres also tended to be smaller in diameter and length at the later stages of processing. As the settling velocity of a fibre depends on its fibre diameter. the median diameters and the overall diameter distributions suggested that on diameter criteria on(v (i.e. excluding factors which. might influence in- terception and diffusion), chrysotile encoun- 1 tered during caqiing was potentially the \ more respirable of the fibres examined. (3) The results suggest that for the same airborne mass concentration the total number of fibres to which persons working in a chrysotile textile plam un a carding machine would be exposed would be about 30 times that of a man dumping amosite. Expcri- mentally, chrysotile. fibres do not readily penetrate the lung because they are intercepted. However, the chrysotile fibres in these airborne dust samples had coil diam- Ieters less than 3 p.m (the limit of respirabili- ty). It seems likely, that once airborne. chry- sotile fibres such as those encountered in this study are capable of penetrating deep into the respiratory system. The lower prevalence of radblcgical change among chrysotiie asbestos workers than among insulation workers would sug- -gest. that asbestosis is related to mass ~ther than fibre concentrations. Experimental evidence supports this for amphibole fibres.l!l For the same concentration, amosite workers would potentially inhate up to 31 times more asbestos in mass tnan chrysotile workers. Other fact~rs such as solubiiity. transiocation lind fibre lengtn are also likely to play a role, once the fibre .has entered the lung or penetrated to the pleura. (4) Consideration of fibre diameter alone indicates thilt chrysotilc encountered during carding is potentially more respirable than chcysotile or other fibres at diffcr~nt stages of processing. The rarity of mL-sothclial tumours among chrysotilc miners and millers. when compared to insula1ion workers (Table n. is probably related to some additional factor such as fibre type or the proportion of long fibre in the airborne dust. The. length-diameter matrices for the vari- FMS\ 05148 t. t' .I .:r .I ~t J..J ...4..~ i .' ....:; .. : ~ -~ j J 1 ' ._ 1J f 1 '., I j I i 1 1 1 f ~ .. -~~- L-----~-. "~ ....~-- .iL... lo . . . . . . . . ldjI' Ij I! I l I. .. 1 ' f .I I . Amrrlctm.lndustrial Hygiene As.wciotion Journal ous types of asbestos provided some )nformation concerning t~is. When the fibre types and areas where samples were taken were ranked according to the percentages of fi- bres with diameter less than 0.5 p.m and length greater than 5 p.m present in airborne dust, the following was the result. Percentage of fibres with diameters ( O.S pm and length ~S "m. Amosite application of insulation 18.3% Crocidolite i7.S% Amosite Dumping 17.0% Chrysotile Dryer 1.45% Bagging 1.0% Carding 0.4% If. the combination of length and diameter ( <0.5 p.m diameter > 5 p.m length) was the only factor responsible for the production of mesothelial tumours., the results presented here would suggest that the hazard for the manufacturer and insulation worker using amosite would be similar, but considerably greater than for chrysotile w~rkers. Taking ~netration into ac-c~:mt, there might only be a slightly increased risk for insulation workers over factory workers using amosite. This is supported by epidemiological studies of insulation workers and workers in an amosite plant.27 Conclusion In conclusion, we recognize that the inferences made in this report are based on limited data and may not be supported by more extensive measurement. Nevertheless, the findings are sufficient to show the complexity of interpreting variations in the physical characteristics of fibres. The measure- ment of physical parameters of fibres in various industries is ieasible and observations to test a physical parameter hypothesis arc not in conflict with experimental or epidemiological evidence. Our results so far support the experimental work on animals suggesting that asbestosis is related to the mass of airborne dust inhaled and that primary malignant mesothelial tumours are related to <46S ofexposure to fibres in a specific range fibre diameters and lengths. Acknowledgements We wisb to thank Mr. G. Seibel of the Pulp and Paper Research Institute, who performed the electron microscopy and Miss P. Hempey for valuable technical assistance. This research was supported by a grant from the Institute of Occupational and Environmental Health. References 1. Wagner, J. C., G. Berry, V. TimbrcU: Meso- theliomas in Rats. In Pneumoconiosis, Proceed- ings o/ durlnternotional Conference Johannes- burg, 1969 (H. A. Shapiro, Ed.), p. 216, Ox ford University Press. Capetown (1970). 2. Selikoff, I. J., E. C. Hammond, J. Churg: Mor tality Experiences of Asbestos Insulation .Work ers 1943-1968. In Pneumoconiosis, Proceedings of the International Confrrence Johannesburg, 1969 (H. A. Shapiro, Ed.), p. 180, Oxford Uni- . versity Press, Capetown (1970). 3. McDonald, J. C.. A. D. McDonald, G. W Gibbs, J. Siemiatycki, C. E. Rossiter: Mor- tality in the Chrysolite Asbestos Mines and Mills of Quebec. Arch. Em. Hralth 22.-611 (1971). 4. Meurman, L. 0., !l. Kiviiyoto, M. Hlili:am&. Mortality and Morbidity of Employees Qf An- thophyllite Asbestos Mines in Finland. In BioloKical Effects of Asbestos1 fP. Bogovsk.i, .. J. C. Gilson, V. Timbrell, J. C. Wagner, Ed.), p. 199, International Agency for Research on Cancer, Switzerland (1973). S. Newhouse, M. L; The Mortality of Asbc~s Factory Workers. In Ptleumoconiosis, Proceed- ings of the International Conference Johannrs- barg, 1969 (H. A. Shapiro, Ed.), p. 158, Ox- ford University Press, Capetown (1970). 6. Webstei-, 1.: Malignancy in Relation to Crocid- olite and .A.Inosite. In Biological Effects of Asbutos, (P. Bogovski. J. C. Gilson, V. Tim brcll. J. C. Wagner, Ed.), p. 195, International Agency for Research on Cancer, Switzerland (1973). 7. Selikoff, I. J., C. E. Hammond, J. Churg: Car- cinogenicity of Amosite AsbestoS. Arch. En- viron. Health 2J:183 (1972). 8. Selik.off, 1. J., J. Churg. E. C. Hammond: The Oc1:urrencc of Asbestosis among Insulation Workers in the United States. Ann. N.Y. Acad. Sci. 132:139 (1965). 9. Rossiter, C. E.. L. ]. Bristol, P. H. Cartier. J. C. Gilson. T. R. Grainger, J. C. McDonald: Radiographic Changes in Cbrysotile Asbestos Mine and Mill Worlcrs of Quebec. Arch. En- viron. IJealth 24:388 (1972). ... ,. . .., .:t:-':: i,~j f ..,... I~ ~~ r.'~. 'I . -; ....... . FMSI 05149 ,. 't! ..l !I' l' I :1 ': ..I , . ,.J :I :-: ..j .j i ;. ~ I ~~ I \ 1 ~ n- ....'"' . I .~~J ..... . 'I' 1' . :. 'J . ' l .I . tj ):i i I:' ,. -I ... .... &- .....;.JI,J -.__ ll:-:....,.~ ..,;. ,; ...,..,. 466 ICI. Uanic... P. G .. t'. A. I . M:..f.kcn7.ie. G. Slu:crs. J. H. Kemp. J. 'I. Mm~an. T. P. Oliver: A Kadiulul!io:al Smvcy <f Men Exfli"C<I ltl A,t'IC... &us in N01val llt~o;~y;mk,lfl'it. J. l11<hut. Mccl. 19:214 ( 1'1721. II. f.ntcrline, P. E.. H. Weill: A~ohcMusis in A!ihcstos Cement Workers. In Biulo~itu/ Effects 11/ A.~br.flm, IP. Hob'Onki. J. C. GiiM>n. V~ Timhrell. J. C. W11gner. t:d.). p. 17'1. Inter national Agency for Research on (';.no:cr. S\\ il1erland (I ~73 ). 12. Newhouse, M. L: Cancer among Workers in the A!>bestos Textile lmlu~try. In Biological 1/ct'l.f of .Asb.-.rlul. !P. Hugov,.ki. J. C. Gil~n. V. Timbrel!. J. C. Wagner. t-=&.1.1. p. ::!0~. In termuiunal Ag~m:y for K~'c:aro:h on Cancer. Switzerland (1973). I.l. Timbrell. V.: The lnhalmi1,1n of Fibrous Dusts. Ann. N.Y. ,A,ucl. Sci. /32:255-119651. lllllt', 197$' 14. Timbrcll. V J. W. St..io.lmorc: "the Fffcct nf Shape on Pjlrtidc l'cndmtiun anti l<ctentiun in Animal l.un~s. In lt~lw/,../ l'cmidt., Ill - (W. H. Walton. 1~1.1. l.ln"'in Uro... l.to.l. Suncy. linglano.l I:49 (1<)71 ). 1.5. Wagner. J. C . G. l:lc:rry,, and V. Timhrcll: Mesotheliomata in Rats after Inoculation with Ao;bestos and Other 1\l,.ter;als. llr. J. Comrr 28:173 (1973). t6. Stanton. M. F. and C. Wrench: Mco:hanism.. of' Mesothelioma Induction with Ashc,to~ and l'ibrous Glass. J. Nor/. Ctmccr lmt. 4lt:1'l1 fl'l72). 17. Timbrell. V.: personal .o:on1munic:ation IK. Timbrel!. V.. F. l'10h:y. ami J. C. Wagner: Characteristics of Re~pirahle Ashco;to' Fibres. In Pllrltlllut.'OIIio.\i.~. Prrl<r-r-rl:n~:.~ of tile llllf'r IUIIitmul Cunj.-rctl('(' Jullunn.-.,burJ!. /1169 IH. A. Shapirn. 1:-'.d.). p. 120. Oxfon.l Univ~rsity Pus.-.. ('apetown {19701. 1~. St..io.lmore, J. W.: pc:rM>nal communication .: .I :t l : .I l-1 I I () _-, -' -.... I --I , -.-.,.,--:1 Seventeenth (;raduafe Summer Ses!'>ion of SC.Htis1ics in lhc Hcallh Sciences Th~ scv.:nt~cnth annual Graduat..: Summ.:r Session of Sta:istics in the H..:alth Sciences will b.: hdd at Vand.:rhih l'ni\'l.!rsity. Nash\illt:. T~o:nncsso.re. June 22 tu August I. 1975. . __ Tentative course offerings include elementary and interm..:diah.: bio- statistics. actuarial statistics. demography. sampling methods. n.:s~arch de.; sign. d..:sign or experiments. Bayesian inkrence. categorical data, and health facility statistics. Several of these subjects will be intensi\'e three-week courses. Instructors for the session will include Helen Abbey. Chin Long Chiang. Jerome Cornfield. Wanzer Drane. Margaret Droktle. and Nl'rman Johnson. These courses. at a wide range ur academic and experience levels, arc designed to benefit statisticians. epidemiologists. and health ;cknce per-son- nel. as well as administrators. h!.!alth planners. and other health workers who utilize quantitative da1~1 in decision m~tking uml problem solving. Graduate students. medkal students. ~md tc~:chers in statistics and in the health. medi- cal. and biological sciences will ulsu be interested in the program. The Summ\:r ~ssion is supported hy funds f nm1 th..: U.S. Puh1ic Health Service. -For further information. write tu Or. Charles F. Federspiel. Summer Scssilln cif Statistics. Di,isiun uf Bi('Statistics. Department t!f Prl.!wntivc Medicine. Vanderbilt University. Nash~ilk, Tcnnessce 37232. .;i. -1 1 l I ~~ l I ' ~ t ~ ~ -~ 1 ! .I 'i -~ ......~~ .~,- I T .... ...!..,. , -~--..,.... ~~ . 1r...\. .. .. , ~. ..... .. -............. r .... FMSI 05150 ~- l FMSI 05151