Document qaM8xv2LEGXxyRo7gDygvMnoE

t~: ': ., se-n: 0 U1 00 N U1 ---r ~\ 0 '-..,.~-- ~ .,?cJ' ~ ~ ASBESTOS: THE PHOENIX OF OCCUPATIONAL MEDICINE Harvey B. Snyder, M.D. EXXON COMPANY, U.S.A. ,r The Phoenix was a large sized, male, fabulous mythical bird with a sweet voice and gorgeous plumage. It was sacred to the Sun, was th~ only one of its kind and lived for a long time. At the end of its life it made .a nest of the twigs of spice trees on which it died by setting the nest on fire and burning itself alive. From its body or its ashes or the nest which it had fertilized came forth another phoenix, perfect, but first in the shape of a white grub. The young bird, as soon as it was strong enough, took up the charred body of its father, covered itself in spices, took ashes, nest and all and flew :o Heliopolis in Egypt where it deposited them on the altar of the Sun. It then died, but not before spontaneously producing an offspring. This significant symbol of immortality, albeit totally legendary, has a distinct relationship to the magic mineral asbestos which has been said to have a half-life of infinity. Asbestos has been called the 20th Century mineral for its produc- tion and utility has increased 20 times more than petroleum in the past 60 years. This is startling when we recognize that the mineral is practically indestructible and is capable of producing disease after a period of 20 or more years after exposure. Is the prediction of in- 16 creasing incidence of asbestosis in the future exaggerated? Asbestos was known to the Ancient World. Plutarch refers to the "perpetual" lamp wick.i used by the Vestal Virgins. Pliny writes of a shroud for cremation of nobility and calls asbestos "the funeral dreAs~sbeosftkosingusse". for modern industry was begun in 1868 when 200 tons were produced in Italy. The mineral is of two varieties. Pyroxene is a serpentine fiber, an example of which is chrysotile, and is the bulk of commerical asbestos used. Amphiboles represents the second variety of asbestos and is represented by crocidolite, amosite, anthophylite, tremolite and actinolite. Prcscnlcd al 1hc European Medical Direclora Mccling, Brusscll, Belgium, \976. 2 \L THE MEDICAL BULLETIN The world ;roduction is increasing annually. The largest commercial produc.er is Canada, which has approximately two-thirds of the total world production. Crocidolite, or "blue asbestos", is mined in South Africa and Australia. Amosite is found mostly in South Africa. The largest United States production is in Maryland and California. This variety is anthophylite, (MgFe)7Si~Oi2(0H),, which has long coarse fibers of low tensile strength and thus of little commercial importance. Most varieties of asbestos have these elements present in their chemical compostion. Physical Characteristics of Asbestos Fibers Asbestos has an almost infinite ability to subdivide itself into smaller afld more fibers. Asbestos fibers may be 2 inches or more in length but their attrition is unavoidable when separating fibers from non-fibrous rock. This results in fibers so short that the length is hardly greater than the diameter. Similarly, the diameter of bunches of fibers may be 1/32" or more in fairly crudely processed specimens but break down to l00-l 000 particles - many too small to be counted with the optical microscope. In an air stream a fiber is generally unpredictable since, rather than conforming to the direc- tion of motion like an arrow, it may spin round and round, collecting other fibers to it forming balls of !luff. In addition, asbestos fibers may divide incompletely at the ends, forming "parachutes" that stay suspended in the air. The size of the fiber is critical. Recent studies have shown that fiber penetration of the lung depends on "diameter and curliness". Harshness thus may be important as it may affect the ability of the fiber to curl.' There are many classifications of diseases of the respiratory system. Asbestos fits into the causative scheme of clinical lung disease as a producer of a type of pneumoconiosis and is also a cause of malignant disease of the lungs and pleura. Clinical Asbestosis "T1 e3n: The characteristic feature of asbestosis is diffuse pulmonary fibrosis (alveolar-capillary block), which contrasts strongly with the e0n _nodular fibrosis of silicosis. As a rule, the lesions of asbestosis are most pronounced in the lower and middle lung zones, whereas 00 N emphysema often predominates in the upper zones. In addition to Q) these parenchymatous changes, asbestos often causes a prolifera- tion of the connective tissues in the visceral pleura, particularly in the basal and medial regions. There is no correlation between the - - - -.... O)liiiii'Ht' ...--.,.u,.."o4l'o' w" l ASBESTOS: THE PHOENIX OF OCCUPATIONAl. MEDICINE severity of pulmonary fibrosis and the pleural changes. Severe pulmonary fibrosis may be present without pleural lesions and severe pleural changes with only mild pulmonary fibrosis. \n progressive asbestosis there may be gross pleural thickening with horn-like plaques giving the roentgenogram a highly characteristic appearance. Calcified plaque formation, when bilateral, is said to b..-! pathognomonic of asbestosis, but it does not necessarily develop into the malignant changes o.F-mesothelioma. Theories of Pathogenesis I. The Original Theory of Physical irritation The preser;.::e of the asbestos fibers in the terminal spaces causes irritation and damage to the wails of the alveoli, leading to fibrosis. 2. The Solubility Theory The fibrosis is due to the effects of the silicic acid and metal ions leaching out from the asbestos fibers. Asbestos is relatively more soluble than quartz and coal. 3. The A uroimmune Theory Two concepts are entertained: a. The presence of the asbestos in the lungs and its reaction within the alveolar phagocytes or fibroblasts either produces or localizes abnormal globulin, the presence of which 1..an be discerned by the presence of "rheumatoid factor" in the circulating blood and in the tissues by immunofluorescent techniques. b. The effect of the fiber on the pulmonary phagocytes combined with their being entrapped in the respiratory bronchioles may be a factor in the initiation of fibrosis. The lysis, then, of the phagocyte at this. site releases a "substance" that is not accepted as "self'. 4. Stagnation of Phagocytes Theory This is similar to (3.) but involves no immunologic mechanism in the tissue destruction and fibrosis. The trapped phagocytes disintegrate and release sclerosing agents, lipids and lipoproteins. THE MEDICAL BUI.l.ET'N Pathology Asbestosis occurs in two main anatomical forms: 1. Diffuse Fibrosis -honeycomb (cystic) lung 2. Solid Fibrosis In either case there appears to be first an aggregation of macrophages in the alveolar spaces, followed by a desquamation of the lining epithelium. Asbestos fibers coated with hemosiderin (asbestos bodies) may be seen in a period as short as 16 days after exposure. The characteristic lesion in asbestosis is the asbestos body, more appropriately called the ferruginous body. J. 4. 10 ~ Asbestos t:ibers, unlike shorter particles called asbestos dust, are converted into asbestos bodies (ferruginous bodies) by deposition of yellow globules of protein and iron, producing an easily recognized and quite characteristic structure. But, before this happens, many of the thin and sharp asbestos fibers move downwards to the lung bases owing to lung movements and to gravity. This downward movement is likely to be more efficient and more rapid in the healthy lungs of the active young. Once a fiber has become a ferruginous body it is unlikely to move further, as it is usually too large to be phagocytosed or transported by lymphatics and its sharp points are now blunted by the protein globules. In recent years the term asbestos body has been altered by some to "asbestosis body". This is an unfortunate and unwarranted change, because the great majority of lungs which show asbestos bodies have no pulmonary asbestosis at all, as the findings of many -"T1 3en: studies clearly demonstrate. This supplies a good reason to call the unique pathological lesion a ferruginous body. Recently Dr. I: J. Selikoff has stated that virtually 100% of New York City adults 0ceno have ferruginou~ hodies. Others5 have also made this assertion. Fortunately there is far less incidence of asbestosis.6 N...... There is today an increasing amount of evidence suggesting that '.ess intense grades of pulmonary asbestosis and even minor or :rivial amounts are more likely to be associated with pleural rather .han with pulmonary changes. Pleural thickening associated with asbestosis is usually calcified and has a significant frequency of malignant mesothelioma of the pleura or the peritoneum. 24 ...... w.-. OF OCCUPATIONAL MEDICINE t:. There is a prediction of an increase of limited basal asbestosis, . malignant mesothelioma of the pleura, and mesothelioma of the peritoneum. Signs and Symptoms The predominant symptom is dyspnea. This is not surprising in view of the earlier statement that the basic pathophysiology is an alveolar-capillary block. Asbestosis may also present with signs and symptoms of pleural effusion.6' s Lung function tests9 are highly characteristic and constant, including: 1. Small inspiratory capacity. 2. Decreased MBC but well maintained relative to lung volume. 3. High FEV1 relative to vital capacity. 4. Reduced vital capacity. This is the most sensitive index of the progression of the disease. 5. Reduced diffusing capacity. 6. Loss of compliance. 7. No significant changes in blood gas studies. Radiological Findings 9 1. Interstitial fibrosis. 2. Pleural thickening-plaques. 3. Basal findings >Apical findings. 4. Obliteration of the costophrenic angles. 5. Shaggy cardiac shadow. 6. Thickening of interlobar septa. 7. "Ground glass" appearance, composed of linear markings and small discrete opacities in the lower lobes. 8. Honeycomb appearance just above the diaphragm. In one sludy of asbestosis with 1111 cases, there were 150 cues of pleural plaques. They were found to l more prevulenl on the left side. When calcificalion was extensive il was usually bilateraL Calcilicatic usually involved the parietal pleura primarily. Calcification or plaques correlated to an uposure or mar years before, often 20 or more. UIIIUICfllUJI UIOgllOSi8 1 ~ I. Distinction between asbestosis and other forms of diffuse fibrosis. Scleroderma Idiopathic diffuse interstitial fibrosis . Cystic lung- pneumoconiosis Eosinoprilic granuloma Sarcoidosis Solid fibrosis- M.P.F. 2. fDibisrotisnics)tion between other forms of silicatosis (nodular whorled 3. Distinction between ferruginous bodies and hemosiderosis of elastic tissues which may mimic asbestosis. Rheumatoid asbestosis. In summary, there are a number of short "clinical pearls" which were gleaned from a course on Environmental Lung Disease, given in New York City, I0-12 June 1976. I. The latent period in asbestosis is long - >20 years. 2. A single exposure may be causative. This gives some credencr to the concept of "Bystander's Disease;,. Laws of dose-response are not necessarily followed. 3. Lung cancer is seldom seen in asbestos workers who do not smoke. It is 92 times more frequent in smokers. 4. Smoking is not related to mesothelioma. 5. Air pollution is not a significant factor in cancer of lung. 6. Compared to non-smokers with the same disease a. Fifteen times as many cases of emphysema are smokers b. Ten times as many cases of cancer of lung are smokers c. Two times as man{ "cases of coronary artery disease are smokers 7. Eighty-five percent of mesotheliomas have a history of asbestos exposure. 8. Sputum cytology is positive prior to any x-ray evidence of carcinoma of lung. While the first cases of pulmonary fibrosis caused by asbestos inhalation were reported in 1929, 12 and the first case of lung cancer associated with asbestos was reported in 1935, IJ it was not until 26 FMSI 05828 196814 that epidemiologic studies established the role of asbestos m the development of lung cancer in cigarette smoking asbestos workers. We should remember a point which Professor Ted Ha~ch hr.s emphasized on several occasions, "When the dust levels are very high, almost any measurement is good enough to show a change for the be ter. But when the dust levels are getting low but not low enough, much more attention must be given to using those measurements which are biologically most appropriate." This is almost certainly the position we are likely to have to face in controlling the asbestos dust hazard in the future. REFERENCES I. Gibbs, LeChance, Chrysotile Mine Dust Exposure in Canada, Arch. Environ Health. March 1972. 2. Bruce, T., Occupational Diseases of the Respiratory System, Scand. J. Resp. Dis. 63(Supp): 73, 1968. 3. Greenberg, S. Donald et at, Sputum Cytopathological Findings in Former Asbestos Workers, Texas Medicine 72:39-43, 1976. 4. Gaensler, E.A., Addington, W.W., Asbestos or Ferruginous Bodies, N. Eng. J. Med. 280:488-492, 1969. 5. Langer, A.M. et at, Chrysotile Asbestos in the Lungs of Per- sons in NYC. Arch. Environ. Health 22:348-361, 1971. 6. Leuallen, E.C.. Carr, D.T., Pleural Effusion Study of 436 Patients, N. Eng. J. Med. 252:79-88, 1965. 7. Gaensler. E.A., Kaplan, A.l., Asbestos-Pleural Effusion, Ann. Int. Med. 74:178-191, 1971. 8. Lowrie, E.G. Asbestosis-Pleural Effusion, Ann. Int. Med. 83:735, 1975. 9. Bader, M..!., Bader, R.D., Terstein, A.S., Pulmonary Functior and Radiographic Changes-598 Workers with Varying Degree! of Abestosis, Mt. Sinai J. Med., 37:492-500, 1970. 10. Suzuki, Y., Churg, J., Asbestos Body-Structure and Develop ment, Am. J. Path.. 55:79-107, 1969. 11. Editorial, Asbestos-+Lung Cancer... Mesothelioma, Lance 1:815, 1973. 2 'I THE MEDICAL BULLETIN 12. Cooke, W.E., Fibrosis of the Lungs Due to Inhalation of Asbestos, Br. M ed. J., 2:578-580, 1929. 13. Lynch, K.M., Smith, W.A., Pulmonary Asbestosis: Carcinoma of Lung in Asbestos Workers, Am. J. Cancer 24:51-64, 1935. 14. Selikoff, I.J. et al., Asbestos Exposure, Smoking and Neoplasia, J.A.M.A., 204:106-112, 1968. 15. Biological Effects of Asbestos, Ann. N.Y. A cad. Science, 132:338, 1965. 16. Se!ikoff, I.J. et al, Asbestos and Neoplasia, Am. ~' Med., 42:487, 1967. s'eTn:I 0 (J1 00 N CD 28 I. .. .~ THE MEDICAL BULLETIN ~~.,. II ' i Adequate signs must be posted in areas where asbestos is being ! l used or disturbed. These notices should clearly state that a potential health hazard exists and that personnel should avoid I the area unless they are wearing necessary protective equipment. EXXON ASBESTOS CONTROL RECOMMENDATIONS* EXXON CORPORATION I Acceptable housekeeping procedures must be instituted to minimize the spread of contamination where asbestoscontaining materials are being handled. Such procedures include such steps as adequate wetting of the materials hefore I ' sawing or otherwise disturbing old insulation, the use of I vacuum equipment to collect finely divided material, the use of ~ plastic drop cloths, the collection of debris in plastic bags and the burial of old material in adequately marked disposal areas. Although the importance of eliminating asbestos from new con- struction and of minimizing exposure to "old asbestos" has been emphasized in both formal and informal communications between the cor~orate and regionaljaf0liate medical departments, no f~rmal policy statement has been 1ssued at the corporate level. In sp1te of the existence of different local regulations and a recognition of ~ ,. d ~ ~ ~ ' A monitoring program should be established to assess exposures to asbestos at regular intervals. Employees who are or have been potentially exposed to asbestos should be identified and included in a medical program including a yearly chest x-ray to determine if adverse health effects are occurring. the influence of local customs and economic factors, the need for a corporate position seems evident. Exposure to asbestos must be eliminated or reduced to minimal levels by eliminating its use in ~.J new construction where possible and establishing procedures for the A hazard information sheet should be developed to instruct employees who have to work with asbestos-containing materials about the potential health effects of the material and preventive measures in effect. handling of asbestos-containing material already in use so there is . no health risk to employees or others. ~ The following recommendations are issued for the guidance of all regional affiliate management and medical personnel: . Contractors and their employees who have to work with asbestos-containing materials should be provided with the same information given to Exxon employees and should be requited to adhere to the same protective work practices. Th~ir Non-asbestos containing materials should be used in all new f~ compliance should be assured by adequate monitoring. construction unless their use would create a greater health and . safety hazard by failure to meet insulating requirements. The Research & Eiwironmental Health Division, Exxon 14 Medical Department, has and will maintain and oistribute an ~~ updated list of non-asbestos containing products available on a world wide basis or in specific operating areas. .' "T1 Existing units should be surveyed by maintenance personnel to ~4 s: r1identify where asbestos was used in prior construction. This (/) will enable exposure controls to be instituted when these units ~~. 0 Ccw1ol 0 are to be worked on and there is the possibility of a release of asbestos fibers. f" f Protective clothing and respiratory protective equipment must :. be available to employees who have to work on units when and where exposure to asbestos is a risk. 30 Issued Seplember 9, 1976. I ~--~: "~":-=n'7 . -,. .. "' N. . I ..........! . I , _.&:; eq r-. -C.-:::Z - 1.E!-JI '1> .., -3en: e0cno (.,.) ~ ASBESTOS HANDLING PROCEDURE* Asbestos fibers have been deemed a serious respiratory hazard and control of worker exposure is considered necessary to prevent asbestosis and asbestos-induced neoplasms. Various Exxon affiliates have taken positive action limiting the use of and requiring substitutes for asbestos-containing materials including talc, asbestos insulation materials (all high temperature insulation can be assumed to be asbestos or contain 5% or more asbestos as a binder), asbestos fire blankets, etc. However, asbestos has been used for many years and its presence will be noticed each time insulation must be removed, during turnaround work and sometimes in new construction when asbestos insulation is the only suitable material. At scheduled turnaround, the breaking of insulation and reins: :lling same after piping completions, etc. will entail some exposure to asbestos fibers. Despite the existence of widespread knowledge concerning the potential health hazards of this material, there is significant variation in control measures in effect at the operating affiliates. As a result, Exxon Corporation Medical Department has issued a Policy on the control of asbestos as a guide to the elimination or reduction to minimal levels in lhe use of asbestos in new construction where possible and to establish procedures for the handling of asbestoscontaining rraterial already in use. The following work practices are recommended: (I) Asbestos-containing cements, mortars, coatings, grout and plaster should be mixed in closed bags or other containers. Manufacturers have high temperature mortars packed in plastic bags so that water can be added directly to the bags through a spout and moistened before opening. Moistened mortar is removed as required and mixing is completed in the shipping container. All waste is replaced in this container and sent to disposal at the end of the shift. THE MEDICAL BULLETIN (2) Removal of asbestos insulation or ripping-off procedures must be done in a manner which will minimize scatter, dusting or dispersion of asbestos. After removing the wire clips and bands hofding the jacket, and the jacket from the insulation, the su. face insulation should be wetted. A plastic sheet placed below the piping or structure \<ill serve subsequent clean-up. As many large pieces should be removed as feasible to minimize the number of cuts required. (3) All waste insulation should be placed in dust-proof bags and all clean-up of asbestos dust shall be performed by vacuum cleaners or by wet cleaning methods. No dry sweeping should be allowed. (4) There should be no spraying of asbestos material without precautions to limit the spread of overspray. (5) Where possible, restrict movement into areas where asbestos dust is being generated by roping and signs which read "Keep Out-Authorized Entry Only." (6) Special protective clothing should be provided to employees working in areas where asbestos dust is being generated. Care should be exercised in laundering and other handling of contaminated clothing. Effective July 1, 1976 the OSHA time weighted average (8-hour) standard for asbestos is 2 fibers (> 5/J m in length) per ml of air. A IS-minute ceiling limit of 10 fibers(> 5f..lm/ml) also applies. Since air monitoring may not always be possible the approximate guide in Table II has been prepared as an aid to respirator selection. However, whenever there is any doubt whether these recommendations are adequate or where air monitoring data is available, respirators should be selected to insure that exposure does not exceed recommended standards. ., Air monitoring techniques to determine concentrations recommended in the standard require some sophisticated equipment and 5: ~ skill. Accordingly to minimize exposures, a series of procedures are recommended in lieu of air monitoring. These are as follows: 0 U1 All persons within the work area shall wear personal respiratory 0) protective equipment selected on the basis of potential airborne (,o) N concentrations of asbestos dust exceeding a TWA limit of 2 fibersjml as time weighted average with a ceiling limit of 10 fibers/mi. 32 ASBESTOS HANDLING PROCEDURE Respirators supplied for the specific application should be. cleaned or disposed, maintained and serviced regularly. Whe.n not in use they should be stored in dust proof containers, e.g., a sealed plastic bag. The following classification has been adopted for the purpose of recommending appropriate respirators for the type of asbestos material involved in each operation (See Table 1). Table 1. Classification of Asbestos Containing Materials Group I Oroup II Orouplll Oroup IV OroupV (Applied dry) Molded asbastos Molded calcium slllcalefasbestoa Molded magnesia (85'/o) Molded high temperature Insulating block (Applied wet) Calcium silicate (plastic) 85% magnesia (plastic) Hard-selling asbestos cement Sprayed asbestos Cement asbestos (hard) Roofing sheets Drain ptpes Building boards Asbestos rope. yarri tape and sealing materials (not Impregnated) Asbestos blankets and clothing Asbestos mill board and paper Filter mats and gauzes Resin-bonded and asbestos reinforced material (e.g .. friction linings and electrical Insulating materials) Asbestos gland pecking (Impregnated) Compressed fiber )ointing Gaskets and preformed packing& Table 2. Respiratory Protection Equipment Selection Guide Operation SpraylngfDemolltlon (Confined space) Tearing Out insulation (Confined apace) (Outdoor') Respiratory Protection Required Dry Operation Type of Aabeatol Material Und With Vent. No. Vent. Wet Operation' With V1nt. No. V1nt. 1,11 0 0 c 0 1,11 cc 0 c c Fullface B c c 3 THE MEDICAL BULLETIN Operation Housekeeping , (Confined apace) Sweeping . Vacuuming (outdoor) Sweeping Vacuuming Application (Confined apace) (Outdoor) Material Handling (Confined space) Mixing Waste disposal Charging (Outdoor) Mixing Waste disposal Charging Grinding & Sanding (Con lined space) (Outdoor) Cutting & Drilling (Confined space) (Outdoor) Cutting & Drilling (Confined space) (Outdoor) Banding & Rivetting (Conl1ned space) (Outdoor) Application (Confined space) (Outdoor) Table 2. (Continued) Respiratory Protection Required Dry Operation Type of Asbestos Material Ueed With Vent. No. Vent. Wet Operation' With Vent. No. Vent. All groups All groups All groups All groups All groups 1,11 1,11 c Fullface B Full!ace B A orB Full!ace 8 A orB D c Full!ace B Full!ace B c Fullface B Fullface B A orB B A orB c A orB B A orB Fulllace B Fullface 8 A orB A orB 1,11 1,11 1,11 1,11 All groups l,lf III,V III,V IV III,V III,IV,V Fullface B CorD A orB Full!ace B or C Full!ace B CorD A orB A orB B c Full!ace 8 Full! ace B Aor8 A orB c A orB None A orB A orB A orB A orB Aor8 A orB A or 8 None None None None None None None None Nona A orB A A orB A?rB None None None None None None None None A orB A orB A orB Aor8 Aor8 A orR A orB Aor8 None None None None None None A- Single use 'It face respirator with or without exhalation valve ., B -Air purifying 'It face respirator with replaceable particulate filter C- Powered air purifying respirator. with high efficiency filter D- Supplied air respirator with full faceplece, continuous flow or pressure demand r3n: Notes: - 1 - Refers to any operation performed outside any confined space where natural 0 U1 00 ventilation Is available 2 - Ventilation refers to any mechanical exhaust or dilution unit. When applied to "outdoor" II refers to mechanical ventilation In addition to already present natural ww ventilation. 3 - This Implies a thorough soaking of the material before any operation Is begun. Superficial wetting will not provide adequate control. 34 ASBESIOSiiANULIIH.i IIUI..LlJUII'-~"-~~~---- The following respirators or their equivalent are recommended for use when working with asbestos containing materials. A. Single Use Respirators (Disposable) Manufacturer 3M Willson A.D. Safellne 3M Model Number 8710 1400 R1050 5350 8800 - B. Air Purifying Respirators with Replacement Filter (Reusable) Manufacturer MSA MSA Willson Willson Willson A.O. l.O. Saleline Welsh Welsh Cover CESCO Glendale Model Number 459440 459438 560 1210 1211 R5030 R6030 5265 7506 7406L 1482-F100 94R20 GR2000 Replacement Filter 459595(10) 459321 R60 R10 R11 R30 R30 5905 7500-6 7400-6 F100 R20 F10 C. Supplied Air Respirators With Full Faceplece Manufacturer SurvlvAir 3M Scott MSA Pulmosan Willson Bullard A.O. Lear Siegler Modal Number 9011-13 9811-13 W840 4616-11 801548 460862 A480111 0168 1810 46 R6099 0501-A Operating Mode Pressure demand Pressure demand C'ontinuous flow Continuous flow Pressure demand Continuous flow Continuous flow Continuous flow Continuous flow Continuous flow Pressure demand ' res Add or manuracturen are round in the rollowing ~ection. THE MEDICAL BULLETIN NAMES AND ADDRESSES OF MANUFACTURERS AND DISTRIBUTORS American Optical Corp., Safety Products Div., 100 Canal St., Putnam, Connecticut 06260. Bullard, E.D., Co., 2680 Bridgeway, Sausalito, California 94965. Cesco Safety Products, Parmalee Industries, Inc., P.O. Box 1237, Kansas City, Missouri 64141, Cover, H.S. Co., I07 East Alexander St., Buchanan, Mississippi 49107. Glendale Optical Co., 130 Crossways Park Drive, Woodbury, N.Y. 11797. Lear Siegler, Inc., 714 North Brookhurst St., Anaheim, California 92803. Mine Safety Appliances Co., 400 Penn Center Blvd., Pittsburgh, Penna. 19535. Pulmosan Sa~ety Equipment Corp., 30-48 Linden Place, Flushing, N.Y. 11354. Safeline Products, P.O. Box 550, Putnam, Connecticut 06260. Scott Aviation Division of ATO, Inc., Lancaster, N.Y. 14086. SurvivAir, Division of U.S. Divers Co., 3323 W. Warner Ave., Santa Ana, California 92702. 3M Company, 3M Center, St. Paul, Minnesota 55101. Welsh Manufacturing Co., 9 Magnolia Street, Providence, Rhode Island 02909. Willson Products Div., ESB Inc., P.O. Box 622, Reading, Pennsylvania 19603. In the U.K. the following respirators have been approved for "Se s:"T1 in atmospheres containing asbestos fibers. The list is reproduced en from the Asbestos Research Council Control and Safety GuideNo. 1. Please note that the protection factors recommended in this 0 list are much higher than those recommended by U.S. standards for Ul 01) similar respiratory devices. The U.S. has adopted a more conser- w ~ vative posture on protective factors as a result of a study by Edwin C. Hyatt entitled Respiratory Protection Factors, Report No. LA- 6084-MS.ln this study the protection factors were calculated on the 36 ASBESTOS HANDLING PHU~a;uunc. ,... basis of average penetration of DOP obtained from test subjects during five basic exercises designed to simulate a wearer's head and' facial movements during actual working conditions. PART I Respirators approved for use in asbestos concentrations up to 40 fibers per milliliter (4 fibersjml for crocidolite). These respirators may substitute A or B in Table II. I. Duralair dust respirator, fitted with Type R 1100 dust filter Safety International British American Optical Co. Ltd. Radlett Road Watford, Herts, WD2 4W England 2. Filtasafe single cartridge dust respirator, fitted with FCt fine dust filter Siebe Gorman &. Co. Ltd. Dais Road Chessington Surrey KT9 ITW England 3. Filtasafe twin cartridge dust respirator, fitted with type FC or FC2 fine dust filter Siebe Gorman &. Co. Ltd. Davis Road Chessington Surrey KT9 ITW England 'it . 4. Baxter Filtrex dust respirator, fitted with an encapsulate filter The Leyland &. Birmingham Rubber Co. Ltd. Leyland, Nr. Preston Lancashire, PR5 IUB England 5. Baxter Pneuseal dust respirator, fitted with an encapsulate filter The Leyland &. Birminaham Rubber Co. Ltd. Leyland, Nr. Preston Lancashire, PRS IUB England THE MEDICAL BULLETIN 6. Martindale Type T dust respirator* Martindale Protection Ltd. Neasden Lane London NWIO IRN England 7. Martindale Type U dust respirator* Martindale Protection Ltd. Neasden Lane London NWlO IRN England 8. Martindale Type W dust respirator* fitted with an encapsulated "Ultron" Type B dust filter Martindale Protection Ltd. Neasden Lane London NWIO I RN England 9. Martindale Type X dust respirator, fitted with an encapsulated Type B fine dust filter Martindale Protection Ltd. Neasden Lz1e London NWlO lRN England 10. Martindale Type Y dust respirator, fitted with encapsulated Type B filters, part No. 18006 Martindale Protection Ltd. Neasden Lane London NWIO IRN England II. Safirmatic dust respirator, fitted with a yellow encapsulated dust (Type B) filter Chapman and Smith Ltd. Safir Works East Hoathley, Nr. Lewes Sussex, BNS 6EW England 12. Purair dust respirator, fitted with a yellow encapsulated dust (Type B) filter Chapman and Smith Ltd. Safir Works -n East Hoathley, Nr. Lewes 3: Sussex, BN8 6EW ~ England. 0 (JI ()C) w (JI ASBESTOS HANDLING PROCEDURE 13. Protective RQ 1000 dust respirator fitted with Safeair No. 54 filter cartridge"' Protector Sa'ety Products (UK) Ltd. Protector House 719 Banbury Avenue Slough Berkshire, SLI 4LL England 14. Protector RQ 2000 dust respirator fitted with Safeair No. 74 filter cartridge* Protector Safety Products (UK) Ltd. Protector House 719 Banbury Avenue Slough, Berkshire, SLI 4LL England 15. Protector RQ 200 dust respirator fitted with either RC 54 or RC 74 filter cartridge Protector Safety Products (UK) Ltd. Protector House 719 Banbury Avenue Slough Berkshire, SLI 4LL England 16. Protector RQ 100 dust respirator fitted with RC 54 filter cartridge with exhalation valve identified by the part No. X210/D* Nos. 13-16 are also marketed under the name "Protectair" .' Protector Safety Products (UK) Ltd. Protector House 719 Banbury Avenue Slough Berkshire, SLI 4LL England 17. Dustfoe 66 dust respirator fitted with fine dust filter, the respirator identified by gold coloring of body and marking thereon of part No. 260846 Mine Safely Appliances Co. Ltd. Queenslie Industrial Estate Glasgow 033 4BT Scotland 39 THE MEDICAL BULLETIN 18. Angus DM 662 dust respirator fitted with Angus filter car tridges type "B" Angus Fire Armour George Angus & Co. Ltd. Bentham Lancaster, LA2 7NA England 19. RP 1620 dust respirator fitted with RP 4 or RP 14 fine dust filters James North & Sons Ltd. P.O. Box 3, Hyde, Cheshire, SK14 I RL England 20. RP 1610 dust respirator fitted with single RP 4 filter and twin exhalation valves carrying the mark SP 1022 James North & Sons Ltd. P.O. 80~ 3, Hyde, Cheshire, SK14 I RL England 21. RP 1660 dust respirator fitted with single RP 4 filter and single exhalation valve carrying the mark SP 1022 James North & Sons Ltd. P.O. Box 3, Hyde, Cheshire, SK14 IRL England 22. Draeger Normalair dust respirator, 74/815, fitted with a fine dust filter Type DN 815 Draeger Normalair Ltd. Kitty Brewster, Blyth Northumberland, NE24 4RH England 23. Phoenix dust respirator, fitted with a yellow encapsulated dust (Type B) filter Phoenix Ac~mories (Milnsbridgc) Ltd. 77 Waterloo Road, Pudscy, Yorkshire, L~28 8DQ England 24. Staysafe dust respirator with yellow encapsulated dust (Type B) filter Staysafe & Co., Ltd. 909 Wolverhampton Road -n Warley Worcestershire, 869 9RR es-n:: England 0en w01) 0) ASBESTOS HANDLING PROCEDURE PART II High efficiency respirators for use in asbestos concentrations up. to 800 fibers per milliliter (80 fibersjml for crocidolite)-(see note . below). This respirator may substitute Fullface B in Table 11. 1. MSA Type 3S High Efficiency Respirator, fitted with an Oval Ultra filter cartridge Part. No. 140-0013 Mine Safety Appliances Co. Ltd. Queenslic Industrial Estate Glasgow, G33 4BT Scotland PART Ill Positive pressure powered respirators approved for use in asbestos concentrations up to 200 fibers per milliliter (20 fibersjml for crocidolite)-(see note below). This respirator may also substitute Fullface B in Table II. 1. Martindale Mark II positive pressure powered respirator (fitted with a fine dust filter) Previously listed as the Martin dale positive pressure powered respirator Martindale Protection Ltd. Neasden Lane London NWIO IRN England PART IV .High efficiency positive pressure powered respirators upon which no limits of dust concentration have been placed-(see note below). This respirator may substitute C in Table II. l. Powermask positive pressure powered respirator Siebe Gorman & Co. Ltd. Davis Road, Chessington Surrey, KT9 ITW England NOTE: When selecting the respiratory protective equipment in parts II, Ill and IV above, due regard should be given to the circumstances in which it will be used which may affect visibility and maneuverability, e.g., work in confined spaces and on scaffolding. 41 I. , <~. ... APPENDIX !I .. ASBESTOS DUST Ml\Y BE. HARMFUL TO 'lOUR ~~~EAl.~TH AVOU) BF~EATI-Uf~G DUST WEt~R ASS!Gf,HED P~10TECTIVE DO ~~OT fl&::MA~f~ IN AREA UI~LESS Yl.)~JR \f\fOF~t{ REQ.UH~ES IT FMSI 05837 ASBESTOS !NFORi',JATION r,SSOCiATiGNi North Am~rica . 1835 1\ Sireet, N. W. Suite tiO? \'hlsbingtcn, 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" that jointly considers measures such as risk-benefit tradeoff. minimum reducible health risk, maximum acceptable cost and implicit 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. Economicbenefits consider employment, 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 l J 1 l I 1 I 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 of sheet used in the decision-making process for regulating environmental quality. Informal comparisons of risks 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 alternative 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 J'r~~('nt ~dJre,<.: C~l\tlc and Co<11..('. Jn~.: .. San Franci~cn. 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 conser>"atism in action than is warranted by the objecti e 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 perctpcion;; of risks and benefits. A large spread of personal evaluations should be expected given data deficiencies on risks and benefits. l nformation about ambient concentra- Amerocao lndus!"al Hygiene 1\ssocalicn JOURNAL (38) 4177 FMSI 05838 153 ---------------------------------------------- lions 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. 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 PRESENT STANDARDS I INDUSTRIAL POLLUTION ALTERNATIVE CONTROLS II ECONOHIC BEtlEF ITS EXPOSURE HAZARDS I HEALTH RISKS I MULTIPLE CRITERIA PRESENTATION Figure 1-Risk/benefit methodology: Analytical 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 in effect over an extended 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 gr,;ater 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.' 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. lnd Hyg. Assoc. J {38) April. 1977 select the those o: more, J another, risks. In( evaluation needs and There; limitatior Because I risk-benef1 vehicular< for auto investigati of hazard: struck f person-' and a l individua, ratio. 1 The as the mo willing to Anoth~: represer con; risb corr<.: additio,, claims, bt. public reh the existt acceptanc was not d In the r new appr incorporal American lndu:; FMSI 05839 STANDARDS: J J J reps Jous 0me they pan; ,Jany nake e are nes~. nd is into or all cinity nuch ikcly c\:ere roxy . and hors. kat h ls to to be more :aths. fits of ~ingl~ lt:?S a . The mu,;t ::d. 1;:-; Figure 2-Hazardous waste system. select the most important impacts and exclude the above referenced' ;dies. But it goes beyond those of hopefully less importance. As he learns their scope by including uncertainty factors and more, he may change the list of impacts. Still by showing how various decision-making another limitation concerns weights assigned to approaches can result in different priorities. The risks. Individuals seem to waver in their conceptual model to be presented was applied evaluation of generally low-probability events as to a selection of feasible controls on hazardous needs and perspectives fluctuate. materials, namely, cadmium and asbestos usage There have been few attempts to consider such in the United States. 5 limitations in formal risk-benefit analyses. Because highway data are readily available, risk-benefit studies are most numerous for vehicular accidents and choices of safety features for automobiles, (e.g.).2' 1 One extensive investigation of risk-benefit ratios for a number of ha?ardous events, such as driving and being struck by lightning selected "fatalities per person-hour of exposure" as the measure of risk and a benefit index defined as "value to the indi\idual" in the denominator of a risk-benefit ratio. 1 The benefit in most cases was quantified as the monetary investment that consumers arc 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," "maxim~m socially acceptable risk," "maximum acceptable cost," and "value of human life." willing to support for a risky venture. As shown in Figure I, the analysis starts with a review of present standards and proceeds to Another more formal, theoretical model parallel examinations of the existing pollution represents benefits of an item as the price a svstem and alternative controls that might be consumer is willing to pay for it. 4 As hazards or ;pplied to it. The parallel approach continues !I \ risks increase with item use, its value declines correspondingly. However, there is an additional "non-pecuniary" part of risk, he with second stage investigations of economic benefits on one branch and of population exposures and resultant health hazards on the claims, beyond which the consumer or general other. Finally, the economic benefits and the public refuses to buy or use the item. This implies health risks are combined with other relevant the existence of a threshold level of risk parameters in a graphical presentation of the t acceptance. Whether such a level actually exists multiple criteria affecting the decision. This I was not demonstrated. presentation is applied under a variety of l 1 In the remainder of this paper, we present a possible decision rules to derive acceptable I new approach toward risk-benefit analysis. It standards and develop priority research needs t incorporates risk and benefit comparisons, as in for future improvement of the decisions. I Am~rcan Industrial H1giene Association JOURNAL (38J 4111 155 \ l FMSI 05840 CONTR: ORI Gil CONTR' EFF NATIC When we examine the top box, Present Standards, in more detail, we discover the kind of 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 neces5ary. 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 observed. 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. Whatever 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 was 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. 7 Standards cannot be made very precise until this conversion problem is solved. When 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, water, 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 usc and disposal. The quantities (not all of which are shown in the figure) therefore are additive both vertically and hori?onatally along the different flow paths. This requires some very difficult data search and 156 Am. lnd Hyg Assoc J (38) Aprol. l9Ti Figur recor creat, How' miSS: the d plaus: systL highi be rei base In< dispo pollut tion 1 fabric exam1 also h: the se emissi< brake effecti1 poll uti steps, manuf fabric contro 96% OJ nc>.tion. about millior Suh~ brake I American 1 FMSI 05841 EMISSION SOURCE: f-- CONTROL ~ETHOD: ~-'NUFACTURltiG FACILITIES 1------- FABRIC FILTERS AUTOMOBILE BRAKES SUBSTITUTE MATERIAL ORIGI~AL EMISSJO~S: sq? M!OTRIC TONS 129 METRIC TONS cornROL EFFECTIVENESS: 96% 100% i :FRO~ INDUSTRY. N:. T IOi1AL COST: FROM BRAKES I LOW MEAN HIGH $2.5 l'dLLION $3 $3.6 $52 MILLION $65 $81 Figure 4-Asbestos control costs and effectivenBss. z 0 .- < ."z-' ":uz' 0 u reconciliation work, almost to the point of being I .-l--- 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 i 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 ARE.~S EXPOSEoD -SQUARE KI LO~.ETERS Figure 5-Asbestos air concentrations. be refined. It also provides a first-order priority b?.se for examining alternative controls. material has yet been found. But if one assumes In our analysis, we observe that although land that a material can be found for a 50% cost disposal accounts for the great bulk of asbestos increase, the total extra cost would run to about 1 pollution, the largest source of air contamina- $65 million per year. I. tion is the 547 metric tons emitted from These economic costs have to be balanced fabrication operations. We therefore have against the control program's reduction in examined controls for asbestos fabricators. We public exposure and consequent hazard, which also have examined the possibility of eliminating we also examined. Figure 5 shows the total areas !'the second most significant airborne source: now exposed in the U.S. to various emissions from users of friction products (i.e., concentration levels from industrial sources and l,.',___,] brake linings). Economic costs and operational from brake lining emissions, according to our ) effecti\ eness of control alternatives for these two simplified model of emission sources and air 11 pollution sources were examined in the next two dispersion. Note that industrial sources are more steps, a~ shown in Figure 4. For asbestos concentrated over a smaller area than are brakemanufacturing processes, we ascertained that shoe sources. Total exposure to the population is I_: .. fabric filters are the most effective method to about SO mg/ m3 from each source. ' control emissions.8 They can eliminate about The big hurdle in our analysis, as in most such . , -I .t 96t;:(; of stack emissions. We estimated the total analyses, came in trying to develop a dose- national cost for such a program would run response function to evaluate the effects of these about S2 million per year, plus another Sl exposures. To do this, we looked at death rate J million for monitoring and enforcement. estimates for the three most important causes of Substitution of other materials for asbestos death from asbestos: mesothelioma, other brake linings is speculative since no satisfactory cancers and non-cancer respiratory diseases. "'''"'"' lnjuslroal Hygoene Assocoatoon JOURNAL (3d! 4.'77 157 FMSI 05842 I I I I I UPPER I CV~tF"IDUK I LIMIT I I I l : 7. I /' I/ II I LQ .. ,::>I I I CotjFtL.::~.c~ I r I<~ 6 I I I I I I Ll"" / / / ' / / I ,/ I/ I // ------II ~--~/ / I 0o~/-~---------,o~2Jt-o---~ ..;ol)o ~J_o_c,_~x_1~:.:-:- FIBER- YEt.~s/cc . Figure 6-Asbestos dose-response: respiratory S(Stem disease. 20 --r--.-----.----,-r-----r-- 18 16 ~ ~ 14 .w-..' 0 ~ 12 0w ~ ~ 10 .w~.. 1 I I UPPER / CONF i DEtiCEJ LIMIT 1 I I I I I I I I I I I I I I I I I I I I '=LO"E" CONF I Dt:JOCE ,.,.,.. Ll111,!...-- .--.- ----- 11 .,.. ...... ,., ...... I __...-- / , ,...... .,.. / -----1 ,.. .......""' '"" tOO 150 200 3GO FIBER- YEARS/cc Figure 8-Asbestos dose response: mesothelioma. I. 'I Figure 6 shows excess deaths versus 9 accumulated asbestos dosage for non-cancer respiratory diseases.9 As with most of our data, e I I I ..."' 7 - ~ 0 ~ ~6 0.. 0 "...'. UPPER I IfCONF l DcNCE LIMIT I I I I I I / // / / I // I / LO'ri:O< 1 /co~iFJc~ic:: !..5. 4 I ~I // u";' / ~ ~~ 3 I I I / / ,/ "~~' 2 I I // / / / .... --"' I/ ,,I II // 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 mesothelioma_ 9 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 b.:cause 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 of excess death '/ 0 . __ __i__ _ __L_ __.L. _ _ _ J _ _ _ _._ _ _ 0 1000 2000 3000 <.000 S.".'-=-=- E.0')0 FIBER- YEAR5/cc Figure ?-Asbestos dose-response: cancer (except mesothelioma}. and combining their uncertainties as independent random variables, we arri\'ed 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. llyg. Assoc J (.18) April. 1977 FMSI 05843 r1 I ~- although in fact we h::Jse 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. Ha7arcb from ingestion of food and water \\ere like\\ ise not considered, since most studies of relative k!nrds indicate that the principal mode of er , of retained asbestos is via the lungs.'~!' 40 3.5 u -' ~ ~ 2'5- iI :: 2Cr- ~ 'I~ :;5: I co rinally. we did not consider the effect of population mobility on the hazard. even though peopk with 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 tradcoffs is illustrated in Figure 10. Here, the two main parameters are measured in the sepaoate dimension of the chart. The vertical scale shows risk in terms of lives saved by a control altern~1ti\e relative to the existing "status quo" situation and the horizontal shows negative economic benefit (or cost) involved. Each alternati\c, staroundcd by an ellipse representing the confidence limits, can be shown in terms of this tradeoff of lives versus nonhealth economic bendits. The dollar tradeoff between health and economic effects is not chartetl. hut any particular valuation of human life can be represented by a diagonal line original ing at the status quo position. .\llernati"> ~s lying above this tradeoff line would be CCht-efft"cti\c in te;ms of that particular life ">aluatil1n. wherea~ alternatives below the line \\ oLdJ prc~umably not be. Other constraints can also be shown on the chart; these act to restrict the feasible domain with which alternati\ e ,;olutions may be sought. At the top a "minimum reducible risk" line ro.:prcscnh a limit in the number of lives that ~:-LIGMA.~- VE:A.RS PER CU3lC .'1ETER IN AIR Figure 9 -Asbestos dose-response: total MINIMUM REDUCIBLE RISK / ----.......LIMIT / ,...... ' / / / /\ I/ ALTERr<AT IVE A \ I ~,_ u "w' > :::; I I _...e/ \ / MEAN 1 ;J_ I /~ "' /.......... "' -----...~. / / ....."'/"" ..,. \""''/"/ ~"/ o"-/ .::-.o""/""/ ...~'/ _,_ / f..---~/~/--~,-.A:-\1-..,-U~-~-AC_C_E-PT-A-BL-E-.-SOC_I_A_L_R_I_S_K / :oST (r.~N-HEALTH DOLLAR BENEFITS) Figure 10-Mufliple criteria comparison method. might b~ 5avc:d by any feasible alternative. The mir;imum reducible risk might be considered as a background !t::vel of contamination below which further reductions arc extremely difficult. At the opposite side of the feasible domain, the "m<t.Xit:mm acceptable social risk" represents a 159 '? .-( i -"*. FMSI 05844 . ~0 11AX1MUM P05SIBLE LIFE SA"IN::; 20 FlLTEP.S ON FACTORIES/ ..\ 1.0 I \ I\ II I >I II 05 I I \,,, I IO NATiONAL COST PER YEAR (:1!LLIO~i S) Figure 11 -Asbestos pollution conrrof a!ternativ=s. 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 considc:red 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 of the two altc ;natives differ by more than 20: I. If one wishes to assign a value to saving Eves, the chart shows that the factory filter alternative costs less than S 10 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 quallfy our conclusions. First, we have not considered potential effects of these measures on the health of industrial \Vorkers, which very likely would be more significant 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 t\VO alternatives. Calculations based on our e.xposure 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 II). This potential life saving is 50 times as great as we get from either of the two alternatives considered, so addition::tl 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 l0 and ll, a full presentation should include the listing of many supplementary criteria by which decision makers or oth:::r interested parties can d~Tiv::: their own values. Such a list is shown in Fi!ure 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\ c'd 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 ordinary old fashioned biases such as optimism. pessimism and probability. So many sdectior. methot.ls are available. in fact, that dccisior. makers in some ways will hav<:: greater freedom 160 Am. lnd flyg. Assac J {38J A~<il. \9~; FMSI 05845 ,, L HAU8DS A'JCllDEO " HEALT-t B. EfN 1;w~;~:_~,Tf.L I I . COSTS OF C0~0I~OL A, DIRECT B. I t:OI RoCT c. MARKoT STRUCTU~:: Ill. BErlF l TS LOST IV. DISTRI9UTIG" OF BENEFITS & COST Figure f2 .. Display of benefits and casts. t l. i j ' -' of action than they ever had before. The choice among alternatives may remain ambiguous. But at least decision makers will have explicit, qu~!ntitative means for weighing the practical tradeoffs that in the long run are going to have to be considered. references Staff. C.: Social Benefit Versus Technological Risk. Sci 165.1232 (1969) 2 lave, LB. and W.E. Waver: A Benefit-Cost Analysis of Auto S8fcty Features. Appl. Econ 2:1 (1970). 3. Calibresi, 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 f\,1oll~ K.D .. S. Baum. E. Capenar. F.S. Dresch and R.M. Wright: Hazardous Wastes. A Risk-Benefit Framework Applied Ia Cadmium and Asbestos. Stanford Research Institute for Environmental Protec;ion Agency (September 1975). 6 Davies. J.C. ed: Decision Making for Reguliiting Chemicals in the Environment. Chapter 5 <>nd Appendix H. National Academy of Sciences. \\'ashington, D.C. (1975). 7. Background Information on the Development of Natonal Emission Standards for Hazardous Air Pollu!;,nts. Asbestos. Beryllium. and Mercury. APTD1503. Office of Air and Water Programs, U. S. Envirvnm,nt~l Protection Agency. p. 34 (March 1973) B. Paddock. R.E. et ai:Corr.prehensive Study of Specified Air Pollution Sources to Assess the Economic l"'pact of Air Oualtty Standards, Vol. II. Asbestos. E!~ry!IIUtn. Mercury. PB-222 858. prt>pared for U.S Environmental Protection Agency by Research Triangle Institute (August 19721. 9 Enterline, P. P. DeCoufle and V. Henderson: Mortality in Relation to Occupational Exposure in the Asbestos lc:dustry J Occup. Med 14:897 (19721. 10. Bruckman, l. and R.A. Rubino: Rationale Behind ,1 Proposed Asbesros 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. LJ.: Asbestos Criteria Document Highlights ASSE J. (3)'26 (1974) 12. A Study of the Problem of Asbestos in Water. by the America" \Vater \'Vorks Association Research Foundation. A ',1. Water Works Assoc. Vol 66. No. 9. Part 2, p. 1 (S.,::>tember 19741. 13. Merliss. R.R.: Talc-Trea:ed Rice and Japanese Stomach Cancer. Sci. 773.1141 {19711. 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. 2281019 !19741. 15. Thaler, R. and S. Rosm: The Value of Saving a Life: Evidence fr.:Jm t:-te Labor rv1arket. paper presented 30 November 1973. publtshed by University of Rochester. 16. Melinek, S.J.: A Methodo!EvaluatingHumanLifefor Economic Purposes. Fire Research Note No. 950. Herts. Er-;land (Nov.,mber 1972). 161 FMSI 05846 l.. ' A method is described for calculating confidence intervals for particle or fiber concentration, and for dust collector penetration. The span of the interval depends upon the value of 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 f t l r l ~t '<>n !: Introduction The concentration of particles in a gas can be determined by passing a known gas volume through a filter and counting particles on representative filter portions. Particle concentrations 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 du.;t. collection Je> i..:.o by making counts of simultaneous upstream and downstream samples. For both applications, it is important to estimate the count reliability. Although enough particles must be counted to establish the validity of the result within acceptable limits, it is wasteful to insist upon excessive counting to obtain needlessly high reliability. Particles for microscopic counting are conveniently collected on membrane filters 12 or electron miscroscope gridst.a.t. The "stratification" particle counting method';_, illustrated i~i Table I is often uset! to reduce counting time. An initial traverse is made by examining a representative number of fields under the microscope. All particles seen are segregated into convenient, continuous size categories. Subsequent traverses note entries for only those size ranges in which particles are present in relatively small numbers. The average number of particles in each size range per traverse, x, is then calculated as shown in Table I. Stratified counting i5 a way to emphasi7e those particles whose concentrations arc most difficult to assess with statistical reliability because of their relative rarity. Nomenclature A - inverse of the fraction of total filter area examined per traverse G -inverse of the total volume of gas passed through a filter m - number of an equal area, counting outward from filter center M - t01al number of equal areas into which a filter is divided David Leith, Assistant Profes sor at the Harvard University School of Public Health. holds Bachelors and Masters degrees in chem ical engineering from the University of Cincinnati, and a Doctorate in Environmental Health Sciences from Harvard. His interests lie in industrial hygiene and air pollution control. American Industrial Hygiene Association Journal Melvin W. First, Professor of Environmental Health Engineerins:: at the Harvard University School of Public Health, is a diplomate of the American Academy of Environmental Engineers and a Director of the AmerIcan Board of Industrial Hygiene. Or. First was a Di rector of AIHA from 1964 1967. 10~ FMSI 05847 I I I .I I I ')" cal r TRAVERSE 1 2 3 4 5 6 Total, N Mean Count per Traverse, TABLE I Data Tabulation for Particle Sizing by Stratified Countlng5 PARTICLE SIZE flANGE, MICROMI:.TERS < 0.45- 0.63- 0.89 1.30 LBO 2.50- 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 57 87 54 36 21 24 6 12 0 12 6 3 3 2 2 1 24 18 18 11 7.10 TOTAL PER 10.00 TRAVERSE 3 300 0 21 03 13 13 23 7 333 57 87 54 36 21 24 9 9 1.8 1.2 300 X Std. Deviation of Mean, l1i" 7.55 9.33 7.35 6.00 4.58 4.90 2.12 2.12 0.55 0.45 95% Confidence Interval 72 105 68 48 30 34 13 13 2.9 2.1 to to to to t> to to to to to 42 69 40 24 12 15 4.8 4.8 0.7 0.3 . ; . _,-~ n N p Paown Pt rm rr X -number of traverses performed in a str::tifieti ~:ounting procedure -total number of particles of a certain size counted through all traverses - N for filter downstream of a particle colkdor - N for filter upstream of a particle collector - number of particles per volume of gas - P for gas downstream of a particle collector - P for gas upstream of a particle collector -dust collector penetration (1 - efficiency), Puown/Pup -distance from center of filter to point where microscope is to be focused for equal area m - radius of filter -number of particles in a certain size range present in one traverse - menn nurr;~~r vf pqrticlcs in a certain size range found per traverse - standard deviation of x -standard deviation of i -standard deviation of Pt Microscopic field selection When a filter holder has a small diameter inlet relative to the filter diameter, the largest particles may concentrate on that part of the filter directly downstream of the gas inlet. Dennis and co-workerss found that such radial concentration gradients did not occur for particles smaller than 20 micrometers diameter 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 small 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 unbiase(l estimate of particle concentration when a sufficiently large number of fields is examined. However, the same result can be obtained with fewer fields by an ordered approach. Because the pressure drop across a membrane filter is sufficient to assure uniform gas velocity normal to the filter surface, the volume of gas flowing through each equal, concentric area on the filter will be the same, unless the central areas become plugged because of excessive particle deposition there. The overall dust concentration for the gas sampled will be the average of the concentrations found in the gas passing through each of the equal areas. To utilize an ordered approach, the microscope should be focused at the center of each equal area ring present in the sector, and a single field examined. After one field in each equal area has been inspected, all data can be combined to make an entry for one traverse, as shown in Table I. lCH February, 1976 ...., \... FMSI 05848 Additional traverses arc made along different radii of the filter sector. 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 a round duct. Average gas velocity could be determined by measuring the velocity at many 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, it is as logical to use an ordered approach for locating counting fields on a membrane filter as it is to use it for locating pitot-static measuring points in a duct. The distance, rm, from the center of a filter of radius rr to the midpoint of each of M equal areas can be found from r; = ~2";;:; 1 (1) 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 95% confidence intervals After stratified counting procedures have been 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 devices, improper microscope calibration and th..: like can be minimized through careful experimental technique. 11 Assignment of particles to improper size categories is not a significant problem when trained observers use a standard Porton graticule for determining particle diameter. 12 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 comprising in traver.~cs. A Poisson distribution describes the variation in these x values 1 ~ 14 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. a= ..j-=;- .. (2) The standard deviation of the mean. u-; , is the standard deviation, u, divided by the square root of n, the number of traverses. F.a-x = = ~ ~ (3) ,-1From Equations 2 and 3, -u--=; -=\ -=- = ~V-1 x nx (4) where N is the total sum of all particles in a certain size range counted through all traverses. Equation 4 is an application to stratified counting of the expression given by Chapman and Ruhf for the relative error associated with repeated counts of particles in liquid suspen- sion. Is Appropriate values for the standard de- viation of the mean, u-; , are given for the data shown in Table I. The number concentratioI 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, A, of the fraction of total filter area examined per traverse, and to the inverse, G, of the total gas volume passed through the filter. P =x A G (5) The standard deviation of a product can be found from 16 u/-) )( :\A~) 2 = ( 2 = (a~ 2 + ( a; ) 2 2 + ( CTGG ) (6) 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. (7) American Industrial Hygiene Association Journal lOS ! ! ! I l ! I I I I FMSI 05849 0.6 rn"TTI----r-.,......-.,TTirr--..-.,..-,,........,..,.,.., z u li u O..IL .... 0 0.1 bO..pj B ~ .~..JO.Ol 5 10 100 NUMBR OF PARTICLES COUNTED, N Figure 1-Number of particles counted versus relative error of particle concentration. ; ~~I \I\\\\\\~:."."l (/) w u...J 0:: ~~ ~~ u. 0 =~ 10 10 100 1000 NUMBER OF PART:CLES 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 penetration as parameter. A 95% confidence interval about P will extend plus and minus 1.96 times the standard deviation for P. 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 standard. 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/SO)Y, 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 stanuard is met is sufficient. Equation 4 can also be used to determine confidence intervals about an experimentally detennined value for dust collector penetration or efficiency. Penetration for particles of a certain size is the ratio of particle concentration in tf".t> downstream gas to the analogous concentration in the upstream gas. Pt P.... -- - -Pup- (9) The standard deviation of this quotient is16 ( uPPdIInowwnnf1PPu1n1n) 2=(~) Pt 2=(~)2 Puo + (10) P ce:: !.% ? JIIN (IS) Figure I is a plot of the relative standard error of particle conce1:tration, o-P/P, against the number of particles counted, N. Applications When asbestos fibers arc counted to determine compliance with an applicable standard, it is prudent to determine periodically the mean fiber concentration and associated confidence interval. The count should be continued only The substitution of Equation 7 into Equation 10 yields <T Pt J> - t"V_N/J:::- + 1 N...... (11) 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/Nu, + 1/N..., (12) 106 February, 1976 c d t: il FMSI 05850 1 Equation II 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, Nup, and downstream, Nd,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 II and Figure 2 show, for example, that to be 95% confident that pentration of particles in a certain size range is between 40 and 60% ( 1.96 <TPL = 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 oarticles that must be counted to achieve a gi~en 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 toN""' 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;~.:rse~ for that filta 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 particles 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 value of <TPt 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'; 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 the 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 I. SILVERMAN. l., C. E. Bli.LINGS and M. W. FIRST: Particle Size Analysis in buluJfrial Hy!!icne. Academic Press, New York. ( 1971). 2. EDWARDS, G. II. and J. R. LYNCH: The Method Used by the U.S. Public Health Service for Enumeration of Asbestos Dust on Membrane Filters. Ann. Onup. Hyg. I I:l ( 1968). 3. MORROW. P. E. and T. T. ~JI'RCER: A Point to Plane Electrostatic Precipitator for Particle Size Sampling. A 111. Ind. llyg. Assoc. J. 25:t\ ( 1964). 4. BILLINGS, C. E. and L. SILV~RMAN: Aerosol Sampling for Electron Microscopy./. Air Po/lut. Control Assoc. 12:586 (1962), American Industrial H)glene Association Journal 107 t II'. ! I I I 1 I 1: I I I r FMSI 05851 5. SICHEl. 11. s.: On the Size Distribution of Airborne Mine Dust. J. S. Ajr. lrrst. Min. Met. 58:111 (1957). fi. I!OEL,P. G.: lrrtroductiorr to Mt~tllt'IIWiical Statistic.~. Wiley, New York (1949). 7. WlllTnY, K. T.: Dercnuirrmiort of Particle Si;;e Distributiorr-Appamtus llllll Ttdllliques for Flm1r !IIi// Dust. Univ. of Minn. Eng. Expt. Station Bull. No. 32 (January, 1950). 8. DLNr-JlS, R., l. SILVERMAN, C. E. UllllNGS, E. KRlSl"Al. D. M. ANDFRSON AND P. DRINKER: Air Clecmiug Studit.< Progress Rcport for July I, 1955 to Juue 30, 1956. A. E: C. Contract No. AT00-1)841 (March 16, 1959). 9. American Conference of Governmental Industrial Hygenists: lrrclrwrictl V<utilmion. 13th ed. P. 0. Box 453, Lansing, Michigan ( 1974). 10. HEMLON, w. c.: Plantmrd Process Ventilcuiorr. 2nd ed. Industrial Press, New York (1963 ). II. II.,WKSLEY. P. G. W., S. 11.\llZlOCl\ anu J. U. ni.ACI.:ETT: Mtll.l"lll't'IIIL'IIt of Solids irr Flue Gt~st'S, British C'oal Utilization Research Assn., Leatherhead, Surrey, England (1961), 12. FAIRS. G. L.: XII-Devclormcnts in the Technique of l'articlcsize Analysis by J\1 icroscopical Examination. J. Roy. Microsmp. Soc. 7/:209 (1951). 13. CORN. M.: Statistical Reliability of Pat1icle Size Distributions Determined by Microscopic Techniques. Am. IIIli. Hyg. Auoc. J. 26:8 (1965). 14. IIERDAN, G.: Smull Pctrtide Stali.ftic.<, 2nd ed. Academic Press, New York (1960). 15. CHAI'MAN, H. M. and R. C. RUHF: Dust Counting Reliability. Am. Ind. Hyg. Assoc. Qttart. /6;201 (1955). 16. AR;o;IN, H. and R. R. COLTON: Statistim/ Met/rods. 5th ed. Barnes and Noble, New York (1970). ,l,~c.epted October 15, 19i5 . submission of new manuscripts The American Industrial Hygiene Association JOURNAL, as the official publication of the Association, provides a medium for timely publication of scientific articles and technical reports covering the broad field~ of industrial hygiene and occupational health. These relate to the detection, evaluation and control of problems concerned with occupational, environmental and radiological health, as well as air pollution, human and animal toxicology, product safety and related subjects. Worthy contributions to the literature are welcomed. Manuscripts will be acknowled!!,ed and reviewed for acceptance promp1ly. When approved, they will be scheduled for publication at the earliest possible date. Only manuscripts submitted exclusively to the AIHA JOURNAL, not published elsewhere and not being considered by another publisher will be reviewed. Manuscripts not meeting these stipulations shoulu not be offered. Detailed guidelines covering manuscript preparation to suit the new format requirements of the JOURNAL will be published frequently. Reprints cf guideline~ also are availabk to authors. Thc~e current guidelines should be reviewed carefully and observed, before the final draft of a manuscript is prepared. Requests for reprints of guidelines for authors and submission of manuscripts should be made to the editor, American Industrial Hygiene Association JOURNAL, 66 S. Miller, ~d., Akron, OH 44313. Galley proofs will be provided for final reading, but not for rewriting or revision, just prior to pu<>lication. Reprint orders ~re made available to authors with galley proofs. Inquiry regarding current status of a manuscript previously submitted for consideration should be made in ll'ritirtg. Be sure to mention the manuscript's JOURNAL number, if known, plus the first author's name and the manuscript's full title. I .I I I 108 t i February, 1976 FMSI 05852 \... ..... -- .... v. 1975 :nt in V. P. Ilea/Ill :Ana/. d. lly 'ygil'll(' Sonna Mark: Counting Asbestos Fibers hy the M-ost Probable Number Method PARKER C. REIST, Sc.D. l><parlmrnl nf E111'imllmr111af Scie11cn a11tl Eugi11crring, U,;,.,.,._,ity of Norllr Camli11a, Clrape/lli/1, Nortlr Carnli11a 27514 A procedure for evnluutinJ: u.~bestos fiber counts Is described which uses the most prohahlc number method of bacteria counting. This tedmi<tue is faster than conventional conntin.: methods, with apJlroximatcly comparable uccumcie~, nltbou.:h it suffers from a lack of rl.:or and requires the observer to estimate iiher coucentrnlions to within an order of mn.:nitude before countin~. For the routine a.~ses.~ment o[ a lar~e number of &.\bestos samples this procedure would seem to be more desirable than conventional l'ountin~ because of the economy of time as well as being easier on the observer. Introduction RECENT FINDINGS ON THE TOXICITY of asbestos have led to increased interest in sampling and analytical proccd ures for determining the concentration of asbestos fibers in air. The Occupational Safety and Heallh 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 standard will be lowered to 2 fibcrs/cm3 on July I, 1976. Evaluation of asbestos fiber concentrations in air is carried out using samples collected on membrane fillers and viewed with phase contrast illumination at 400X-450X. 12 This method is the standard field sampling method adopted by the Public Health Service. Fibers arc assumed to be distributed randomly over the filler 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 collected, more than I00 fields would' have to be viewed if one were to find 100 fiber!! on a 10 minute sa~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 asscsscd.3 Of course, the number of fields necessary could be decreased py increasing the sampling time-i~:>'. the latter case a 90 minute sample would yield 100 fibers in 50 fields-but the flexibility of shortterm samples is then lost. 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 particle having an aspect ratio of three or greater is a fiber). H the 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 of fibers, then~ is another quite distinct statistical method which could be used for estimating the number of fiber~ randomly distributed over a surface, the ~o-called most probable number method. In this paper the method will be applied to asbestos fiber counting 379 FMSI 05853 I 380 May, 1975 and the auvantagcs anu limitations of its usc will he uiscusscd . 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. Chapman6 applied the method to dust counting but it was not received with much enthusiasm for reasons which will be uiscusscd later. Most recently the technique has fallen into disfavor even for estimating bacterial concentrations 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. Consiucr a filter of area A which is 'broken up into a fields. Jf there arc m fibers distributed randomly over the filter surface, then the average number of fiber:; per field, /,is I =.!!!. a (1) The probability, P, than 11 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) 1f the voiu fields are distributed randomly across the filter and L fields arc sampled, the probability that exactly I of these fields will be void is Pr(o) = l! (LL~ m[P(o)]1 [ 1 - P(o)] <L -1) (4) Equation 4 gives a distribution of probabilities which is very small for small I and rises TABLE I 95% Confidence Interval for a Given Average Number of Particles Per Field Particles/ Field True Average L = 25 95% Confidence Interval Expressed as a Percentage of the True Average (ldt column, minus; right column, plus) L = 50 L= 100 L = 200 0.1 100 - 229.1 75.8- 138 56.7- 84.9 43.3 - 51.1 -0.2 76.6- 156 .58 79.7 41.3- 51.7 29.8- 3.5 0.3 (,9.6- 111.3 49.9- 58.8 34.1 - 43.1 25.9 -- 28.1 0.4 54.8- 90.3 42.1- .59.8 31.5- 36 23.1- 2.5..5 0.5 .56.3 - 79.4 41.1- 52 27.8- 36.2 21.8 - 22.6 0.6 .52.7- 76.2 37.4- 40.8 27.9- 33.6 18.7 - 22.8 0.7 47..5- 5.5.2 35.6- 47.4 23.9- 32.2 18.8 - 21.7 0.8 45.6- 73.8 33.6- 311.8 25.1 - 31..5 18.1 - 21.2 0.9 44.3- 7.5.6 32.8- 38.9 22.3 - 31.4 17.6 - 19.4 I 43.2- .57..5 32.2- 39.7 21.9- 31.7 17.4 - 19.5 1.1 23.9- 28.7 17.4- 18.1 1.2 21.11 - 29.6 16.3- 18..5 1.3 22 -26.8 . 16.5- 19.2 1.4 23.3- 28.4 1.5.6- 18.1, 1.5 22.6 - 29.9 1.5.9- 19 1.6 20.9- 26.8 .. 16.3- 17.9 1.7 21.4 - 28.7 16.11-19 1.11 22.1- 2.5.6 16 -20 1.9 20.2- 33.1 1.5.2 - 21.4 2 23..5- 30.3 1~.7- 20.2 Amt'r/ca to somt small a that ha' Turning conccnt The; pic pr<X tion. P dctcrmi1 present the natu fields s fields c< most p1 can be As tl creased, creases. range fo at vario Equatio 100 fie 30% rcgardlc provide< density Figun: micrOSCOI FMSI 05854 t I Amcrica11 lllrltulriiiii/.I'Ki<'ll<' A.uochtlioll Jolll"tllll 3Rt to some maximum value before becoming small again: The most likely probability, that having the largest value, m:curs at l = Le-1 (5) Turning this arounu, the most probable fiber concentration is thus f = /11 (-L1- ) (6) The above development results in a sim- ple procedure for assessing fiber concentra- tion. A number of fields arc scanned to determine only whether fibers arc or arc not present in any given field. Then by taking the natural log of the ratio of the number of ficlus 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 ficlus scanned is in- creased, the accuracy of the estimate in- creases. 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 example1 assaying 100 fields will yield results within about 30% of the true value 95% of 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 I. Vllriuus oricnlutions of fibers in lhe mi..:ruscorc fio:l<l. ficlu or less. Ao;saying 200 ficlus will in~rcasc the accuracy of the 95% confiucncc interval to something less than 20% of the true count. For the case of L = 200, the accuracy a:p- pcars to increase with an increasing average number of particles per fielu. This---Will continue until the point is rcachcu where there is a good chance that every field contains at least one fiber. This occurs when the average number of fibers per fielu is slightly in excess of three. Thus for this method it is necessary to estimate ahcau 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. Definition of a Field Containing a Fiber Thus far,. for the purpose of development of the theory, fibers have been considcreu as if they were particles. But they are not. A fiber has length and as such may start'in one field, extend through another or several others and finally terminate in yet another field. Figure 1 illustrates such a situation. The fiber originates in the upper left 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 that 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 sid~~ of the fiber would be appropriate. A field would be considered. blank if the lower end of a fiber were not in it. Thus, in Figure I, only the fields on the upper right hand side and lower right hand side would pc considered, to contain fibers. Since each fiber is asso- ~---v ........ - -. . . . .- - - FMSl 05855 ." 382 ciateJ with one "lower" end, the estimated number ends would equal the estimated number of fibers. t\ second approach would be to call a field void only if it contained no fiber ends at all. In Figure I only the lower left hand field would be considered to be void. The most probable number of ends would then be estimated and since cuch fiber has two ends, the most 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 May, 1975 whether the fiber is 111 the field or not. EXJICrimcntal In order to determine the erricacy of the proposed counting procedure a number of asbestos samples were cottnlcd using a direct counting method <md a record was kept of the number of void fields observed. Most probable number data as determined from 120 FIELDS COUNTEDl 0 00 0 0 .0.....J.. .."..' zo .~ II ~ II .r..i ~ 1.4 ..:z:> z"' I ..J ..~I 0 ti; 0.1 0 " 0. 120 FIELDS COUNTEDl 0-l.tPN A-IHHECT COUNT 0 0 0. O.l ~~-=~~-=-~~--~~~~~ 0 02 04 01 01 I 0 I Z 14 II II 1.0 DIRECT COUNT, FIBERS PER FIELD Fi~:ure 2. Mw.t prohahle number dat:1 11~ determincll rrom Equution tl versus direct count. I DIRECT COUNT, fiBERS PER FIELD Figure 3. Plot of most probable number versus direct count for data from computer simulation for 20 fields. 0... :t ~ ~ .'!..! <i ~ ..z "J ..~ ~ I t; 0 :II CIDO "ELDS COUIIT01 -"- - - ,--::- :..:=:---- -::=-=-=--~r~-:--::-=---~ II ) DI~[(T COUNT, FibERS PER FIELD Figure 4. Plot of most probahle 1 number versus direct count for duta from computer simulation for 1011 field,, FMS\ 05856 Amcrit'an ltulu.rtrittl 1/y~;il'lr<' A.uociatim1 loumal Equation 6 arc plott~u as a function of the uircct count which was ohscrvcu 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 data, the general reproducibility is apparent. However, it appears that the most probable number mcthml 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 difference could be due to failure to sec 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 density. Then fields of various sizes were randomly chosen and 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 IZOO fltlDS COUNTEO I 'I 0 ...~~. ! j' ' ~"' I \1 " 0 Figure S. l'lot 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 experimental data, however; there appears to be no bias toward the direct count information, indicating that the higher count averages n_oted 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. Advantages and Disadvantages The advantages of the most probable number method arc threefold. Sampling times arc 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 iimes arc needed in the field, often an 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 less eyestrain for the microscopist since he only has to determine whether there is or is not something there, and not resolve a specific number of fibers. If problems 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 determine particle concentrations about twice as fas't using the most probable number method compared to standard counting methods. whhe another observer was three times as fast using the MPN method. We have not studied counting times objectively, but subjectively 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 faster. The principal disadvantage of the most probable number method is that it is not FMSI 05857 -~ 1 l~ .. 384 rigorous. An observer CO]Jid,' 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 of particles per field, the 95% confidence intervals for the direct counting method arc 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- server to estimate fibers to within an order of magnitude before counting. However, for the routine assessment 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 I. Edwards G. H., and J. R. Lynch: the Method Used by the Public Health Service for Enu: meration of Asbestos Dust on Membrane Fillers. A1111. Occup. llyt:. 11: (1968). 2. Joint AIHA-ACGIII Aerosol Ha1.ards Evalu ation Committee: l{ccornrnendcd Procedures for Sampling anti Counting Fibers. Amer. lud. 1/yg. A.ISOC. J. 36:83 (1975). 3. Annon.: OccllfWiioua/ Exposure to A.fbl'sto.r, p. viii-5, HSM 72-10267, U.S. Dept. H.E.\y., NIOSH. Washington (1972}. 4. McCrady, M. H.: The Numerical Interpreta lion of Fermentation Tube Resulls. /. l11jec. Di.r. 17:183 (1915). : . :'. . 5. Cochran, W. G.: Estimation of Bacterial Den- sities by Means of the Most Probable Num ber. Riomttric.r 6: I05 (1950). 6. Chapman, H. M.: Dust Counting by the Most Probable Number Method. A.M.A. Arc/a. In d11str. Hyg. 8:234 (1953). Inf dot Vi p01 WI tiV4 en. COl em die tm cid hUi rc~ icil tre stu me for the phi be, a{ an4 me tai FMSI 05858 JOURNAL OF PAINT TECHNOlOGY Handling Asbestos Chrysotile Asbestos 1. n Plastics JOHN L. MYERS Union Carbide Corporation* Ashestos_.ha.s.J:eceived_a great deal .of attention and publicity in recent years, especially after it was designated a "target health hazard" by OSHA and a "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. The purpose of this paper is to put the matter of asbestos use and asbestos hazards into a logical and practical perspective. In this paper, the different types of asbestos and their many uses are discussed, along with governm~nt regulations controlling the use of asbestos. The health hazards associated w1th asbestos, both occupational and environmental, and some industrial experience with air sampling and dust control measures are also covered. KEY WORDS: Asbestos; Plastics; Air pollution; Toxicology. What is Asbestos? Asbestos is a commercial or generic term used 'to describe six naturally occurring "asbestiform" minernls that are fibrous, hydrated metal silicates. The six varieties are divided into two classes-serpentine and amphibolebased on their crystal structure. Chrysotile is the only mem'ber of the serpentine class, while the amphiboles include crocidolite, amosite, anthophyllite, tremolite, and actinolite. Chrysotile is by far the most-used variety and accounts for over 95% of U.S. consumption, as noted in Table l. Crocidolite, also known as blue as- bestos, is imported from South Africa. 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 Presented at the Golden Gate Society's Management Seminar held in San Francisco, Calif., June 16. 1975. Metals Di\"., Niagara Fa11s, N.Y. 14302. VoL. 47, No. 611, DECEMBER 1975 insulation. Although there are some deposits of anthophyllite in the U.S., most of it is imported from Finland. It is used primarily atS a filler for polypropylene and in insulating materials. A comparison of the four varieties of asbestos which are of commercial imporrance is presented in Tavle 2. It should be noted that there are significant differences between chrysotile and amphiboles with regard to chemical composition and certain physical properties. Where is Asbestos Used and Why? Asbestos has served mankind for more than 100 years in a broad variety 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 33% of the 800,000 tons consumed annually, which makes it the largest single user of asbestos fiber. The largest uses of asbestos by the plastics industry are in vinyl-asbestos floor tile and in phenolic molding compounds. It is also used in other plastics such as polypropylene, poly ester, nylon, melamine, epoxy, silicone, and vinyl. Asbestos provides a valuable funcliion in such products as brake linin~s, clutch facing;s, electrical components, automotive parts, furniture, boats, sealants, coatings, adhesives and mastics. The most important functions of asbestos in plastics are reinforcement, dimensional stability, heat resistance, How control, and general-purpose filling. Most of the functions are supplied by short-frber chTysotile asbestos fiber, although longer chrysotile fibers and other asbestos varieties are sometimes required for particular properties. Why Use Chrysotile? Among the several advantages of chrysotile, which set it apart from the amphibole minerals and account for its widespread and increasing usage, are world-wide availability, mechanical strength, flexibility, positive surface charge, low iron content, softness, and low refractive index. It is conservatively estimated that chryso- tile asbestos is used in over 3,000 ap- plications and, in most of these applications, it is an essential ingredient for which no replacement is readily available. The information in Table 1 shows that the use of chrysotile asbestos and its share of the total market are steadily increasing. This is due partly to technical advances permitting the broader use of chrysotile in plastics and the general decline in the use of asbestos in cer~ain fireproofing and insulating materials. In addition, there is increasing evidence that crocidolite and amosite are more hazardous ro " ~(t-JI )~i FMSI 05859 Year 1967 1968 1969 1970 1971 1972 Table 1-Apparent U.S. Consumption of Asbestos, Tons Total Chrysotile Amosite Crocidol ite 720,583 817,363 784,321 728,131 758,571 808,554 686,044 (95) b 775,711 (95) 749,708 (96) 695,770 (96) 729,272 (96) 791,020 (98) 12,558 (1.7) 20,467 (2.5) 14,618 (1.9) 14,261 (2.0) 14,580 (1.9) 7.125 (0.9) 14,917 (2.1) 13,965 (I.7) I 0,558 (1.3) 8,936(1.2) 6,953 (0.9) 5,374 (0.7) {a) Information based on import and production data from U. S. Bureau of Mines' Minerals Yearbooks. (b) Percent of total shown in parentheses. Table 3-Apparent U.S. Consumption of Asbestos By General Use Areas Area of Use Percent of Consumption Construction Floor tile Felt paper Friction and packing Insulation Textiles Other 40 15 15 14 ll 2 ll human health l'han chrysotile.' Since 1970, the use of crocidolite in Britain has been restricted after a panel of experts "concluded there was sufficient evidence to suggest other types of fibre should be substituted for crncidolite wherever possible."' What is the Asbestos Hazard? It is readily accepted that asbestos, like many other foreign bodies, can cause disabling lung damage (pulmonary fibrosis), commonly referred to as asbestosis. This disease and bronchogenic carcinoma (lung cancer) are the two most common ashe~tos-related diseases. It is important ro note that, based on epidemiological data, these diseases have occurred primarily in workei'S with high, longterm exposures to asbestos dust. It is of further interest that one noted researcher has reported that nei'ther of these disea<>es is peculiarly related to or caused solely by the inhalation of asbestos fiber.' Another important consideration is the relation between cigarette smoking and lung cancer, as reported by Dr. E. C. Hammond and Dr. I. J. Selikoff! In this study, they reported that: "J.t seems clear, then, that lung cancer is uncommon among asbestos insulation workers who have no history of cigarette smok:ing and that if the risk is increased, such increase is not great." A third disease, mesothelioma, has more recently been associated with persons exposed to asbestos. Mesothelioma is an extremely rare cancer of the lining of the chest (pleura) or the abdominal cavity (peritoneum). In contrast to the lung diseases, there is some evidence that mesothelioma can occur after brief exposures to relatively high fiber levels. According to the 33-memiber Advisory Committee on Asbestos Can- Formula Table 2-Comparative Data for Asbestos Minerals' Chrysotile Crocidolite Amosite Anthophyllite 3Mg02Si0, 2H,O Na,O Fe,Oa 1.5MgO5.5Fe0 7Mg0 8SiO.-H,O 8Si0, H,O 8Si0, H,O Composition, % SiO, MgO FeO Fe,O" Al,O,, H,O CaO Na,O CaO+Na,O 37-44 39-44 0-6 0-5 0-2 12-15 0-5 49-53 0-3 13-20 17-20 2-!i 4-B 49-53 1-7 34-44 2-9 2-5 0-3 56-58 28-34 3-12 0-2 1-6 Crystals Color Texture Flexibility Hardness, mohs Fiber diameter, A Tensile, mpsi Surface charge Resistance to acid Resistance to alkali Fine fibers Gray green Soft silky \'cry good 2.5-4 !80-300 800 Positive Poor Good Brittle fibers Blue Harsh Good 4 600900 600 Negative Good Good Prismatic Grayfbrown Harsh Good 5.5-6 600-900 200 Negative Good Fair Prismatic (;ray Harsh Poor 55-6 600-900 <4 Negatilc Very good Good (a) Sources: Modern Plastics Encyclopedia ( 1973), and Encydopedia of Chern. Tech .. Vol. 2. oers of the International Agency for Research on Cancer (a division of the World Health Organization): "There is evidence of an association of mesothelial tumors with air pollution in the neighborhood of crocidolite mines and of factories using mixtures of asbestos fiber types. The evidence relates to conditions of many years ago. There is evidenoe of no excess risk of mesol'heliomas from asbestos air pollution which has lOOted in the neighborhood of chrysotile and amosite mines. There are reported differences on incidence of mesothelioma between urban and rural areas, the causes of which have not been established. There is no evidence of a risk to the general puJblic at present."' The same body quoted above has also concluded l'hat there is, at present, no evidence of lung damage by asb~tos to the general public; and such evidence as there is does noot indicate any risk of cancer resulting from asbestos fibers present in water, beverages, food, or in the fluids used for the administration of drugs. While there seems to be general agreement that the public is not in any present danger from asbestos, it is also recognized that excessive, longterm occupationa~ exposure oan cause serious health problems. Also, if manmade emissi'Ons aTe not controlled, then environmental contamination could could approach harmful levels. During the past two years, signiflcant legislation bas been enacted by the Federal government to reduce and control occupational exposure to asbestos fibers and to minimize Sber emissions to the environment. Additional st:andards or regulations have been proposed or enacted by many states and looal governments. Summary of OSHA Regulations The WilHam-Steiger Occupational Safety and Health Act of 1970 became effective on April28, 1971, with JOURNAL OF PAINT TECHNOLOGY FMSI 05860 prudent to permit additirmal contamination of the public environment with asbeSitos. Continued use at minimal risk to the public requires that the major sources of man-made asbestos emission into the atmosphere be defined and controlled.' "7 What is Industry Doing? The Asbestos Information Association/North America reports that, during the past 30 years, the asbestos industry has spent millions of dollars to 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. The ultimate goals of the asbestos industry are: Reduction of work-area dust t~ minimum levels; Protection of workers from asbestos-related diseases; :\1aintenance of environmental emissions at levels low enClugh to preclude ptihh endangerment. Air Sampling In order to comply with OSHA standards and to determine 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 concentrafons of asbestos fibers shall be made bv the membrane filter method at 400-450X (magnification) (4 millimeter objective) with phase contrast illumination.''" 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 existing microscope can be modified for "counting" the asbestos fibers in complinnce with NIOSH criteria." Air samples have been collected and analyzed on a regular basis by the ashe9tos industry for years. Ex- cept for a few applications where dust control is an engineering problem, industrv is finding that dust levels are alreadv within acceptable standards or that minimum changes are necessary to achieve compliance. Although data on many asbestos/plastic applicatinns are not available, the summarv in Table 4 is tvpical of our measur~ments of dust levels during asbestos handling in various tvpes of plants and operations. The dust levels reported are cei'ling concentrations, and it should be noted that the allow- Table 4-Typical Air Sampling Results Ceiling Type Plant Concentration, Or Operation Asbestos Fibers/ cc Floor tile Polyester Phen~lic compounding Handling phenolic Caulks and sealants Gypsum compounds l-3 l-3 2-5 3-14 0-8 2-9 (a) Source: Union Carbide Corp., from air mo11 itoring reports. able OSHA level is 10 fibers/cc. In most cases, the TWA exposure level would be well below OSHA standards. Most of the data were collected before the installation of any special dust-control measures. Monitoring often shows that obviously dusty conditions are caused by materials other than a9hestos. This does not preclude the need for controls, but it could change their scope and facilitate compliance with government regulations. Because of "bad press," asbestos is frequently ordered out of use without regard to whether or not a ha2Jard actually exists due to air contamination. If accepta>ble dust levels are feasrble, there is no need to replace asbestos at the expense .of product quality or economic penalty. Gordon 'Everett of EPA points out that information on the biological elfecots of asbestos is very limited and that the effects of manv substitutes have not been investigated at all. Before asbestos is replaced, it should be certain that a safer alternative is avail- able." Obviously there are more people exposed to products containing asbestos than there are to raw asbestos fibers. As noted previously, more than 90% of the asbesros used in this country is in products in which the asbestos is "locked in" or hound with ce- ment, plastics, or obher hinders, so that there is no release, or at least no signifioant release, of fibers in work areas or bo the environment. Materials or products with locked-in fibers would include: floor tile, polyester resins, phenolics, sealants, coatings, brake linings, friction materials, rubher, roofing compounds, and reinforced plastics. Since an abrading action on some of these products could release asbestos fibers, appropriate monitoring and/or control measures should be instituted if it is thought that such action would release fibers. Dust-Control Measures Asbestos producers and users are spending a considerable amount of time and money on various dust-control measures. Conventional means to .tchieve minimum duSit levels include: filtered venti'lation systems on process equipment, local ventilation for saws and similar tools, conversion to a "wetted" operation, leak-proof packaging, vacuum clean-up, more care in bag di~osal and other asbestos waste handling, and automatic bag openers. Unusual innovations include: pelletized asbestos, special packaging, and treated products. Only short-fiber chrysotile is available as pellets, but this product serves a fair portion of the asbestos market. Pellets not only reduce dust during conventional handling but they are also available in bulk hopper oars and can be transferred and used in -totally enclosed systems. Barring leaks in the system, dust in work areas is virtually eliminated. Used in bulk, asbestos pellets also reduce shipping costs, eliminate warehouse storage and handling, facilitate automation, reduce clean-up, and eliminate bag handling and disposal. The pellets contain no binder and are friable enough to be dispersed in dry form or in aqueous or resinous systems with conventional high-shear grinding equipment." Several types of special packaging are currently available, and suppliers consider customer requests for unusual requirements. The floor tile industry can obtain asbestos in plastic bags which oan be added directly to th<e cr1mpounding operation. Asbestos in bleached paper bags assembled with water-soluble glue and printed with water-dispersible ink can be added directly to paper-making finishes or acoustical tile formulations. Although "wetted" asbestos is not generally available, most suppliers are working with customers to provide "dustless" products. When justified bv m~rket demand. asbestos can be tre;ted wirh water. mineral spirits. glycol, or other materials compatible with the application or system. Conclusion Asbestos is one of industry's many raw materials which involves a potential hazard when not used with reasonahle respect and care. Although all forms of asbestos are recognized as hazardous to health when inhaled excessively, there is growing evidence that crocidolite and amosite are more hazardous than chrysotile. Fortunate- .JOURNAL OF PAINT TECHNOLOGY FJVISI 05861 the following Congressional purpose: "To assure so far as poss~ble every working man and woman in the nation safe and healthful working conditions and to preserve our human resources." The Act established the Occupational Safety and Health Administration (OSHA) within the De- partment of La:bor, which has responsibility for administration and enforcement. Research and related functions are handled by the Department of Health, Education and Welfare (HEW) through the National Institure of Occupational Safety and Health ( NIOSH). Five million employers and 60 million of bhe nll!tion's 80 million workers are covered by OSHA. Specifically excluded from coverage are government employees and operations which are protecred under other federal health and safety laws. In a news release issued January 4, 1972, OSHA announced a Target Health Hazards Program aimed at improving health factors associated with working condftions. The following five substances were designated to he the focus of initial and concerted efforts by OSHA and NIOSH: asbestos, oorton dust, silica, lead, and carbon monoxide. At the present time, new standards have been established only for asbestos, although, of the 8,000 toxic substances on the NIOSH li&t, only 500 are covered by standards and many of those need updating. The new Standard for Exposure to Asbestos Dust was published in the Federal Register, Vol. 37, No. 110, on June 7, 1972. The basic exposure standard is an 8-hr time weighted average (TWA) of five fibers, longer than 5 micrometers, per cubic centimeter of air. The TWA limit is to be reduced to two fibers per cubic centimeter on July 1, 1976. A peak concentration of 10 fibers per cubic centimeter is not to he exceeded at any time. All of the fiber concentrations are those to which an employee may .be expused without protective clothing and equipment. The first basic requirement of the new standard is monitoring to determine whether or not fiber concentrations are in excess of the exposure limits. Some asbestos suppliers provide a monitoring service to customers, and a similar service may be obtained f,rom state health department officials, insurance carriers, or private consultants. The law requires that monitoring be repeated as necessary to ensure that employees are not exposed ro levels in e~ss of the exposure limits. Improper interpretation of the regulations has created many misconceptions about equipment and procedures needed to properly use asbestos. If exposure limits are not exceeded, there are no further compliance requirements except for medical examinations. Medical examina- tions are required for all employees in any occupation exposed to airborne concentrations of asbestos fibers. The examinations are relatively simple and should cost no more than $50 per year, per employee. Respirators and special clothing are rcqUJired in the construction trade for the spray application of insulation and fireproofing materials, and for the removal of such materials. This special protection is not reqUJired for any other use of asbestos unless exposure l"mits are exceeded. This is also true for other items such as specially equipped tools, change rooms, clothes laundering, and waste disposal. Respirators are not a substitute for engineering controls, but ~he law allows their use while controls are being implemented, in spedal situations where controls are not feasible or adequate, in emergencies, and for infrequent short-term. job assignments. Caution }abeJ.s are required on products containing asbestos except where the flbers have heen modified by a bonding agent or other material to prevent dusting during any normal su<hsequent use or handling. Besides raw asbestos fiber, products which require pack!age labeling could include: dry acoustical spray products and joint cements, unsaturated roofing felt and textiles, and some insulating products made without adequa~ hinders. The labeling of a prodnet does not prohibit its use. It should he noted here that in at leas-t 90% of the products containing asbestos. the fibers are solidly locked into the product thereby presenting little danger of dust generation during normal use and handling of the product. EPA Standards Whereas OSHA is responsible for the protection of the worker, the Environmental Protection Agency (EPA) is charged with improving the environment to which the general public is exposed. On March 31, 1971, asbestos, along wi'th beryllium and mercury, was identifled as a "ha:mrdous air pollutant" by the Administrator of the EPA. National Emission Standards for asbestos were then published by EPA in the Federal Register, Vol. 38, No. 66, Apcil 6, 1973. Although no numerical emission standards were established, operating criteria are prescribed to prevent or limit asbestos emiSSiions to tihe outside air from asbestos mills, roadways, certain manufacturing operations, building demolition, and the spray-on application of materials used to insulate or flreproof equipment and machinery. The law further requires that spray-on materials used to insulate or fireproof buildings, structures, pipes, and conduits shall contain less than 1% asbestos on a dryweight basis. This should significantly reduce emissions to which the general public may he exposed, especially in large urban areas. "... the Administrator (of EPA) has determined tha!t, in order to provide an ample mar~n of safety to protect the public health from asbestos, it is necessary to control emissions from major man-made sources of aS'bestos ,emissions into the atmosphere, hut that it is not necessary to proMbit all emissions. "In this determination, the Administrator has relied on the National Academy of Sciences' report on asbestos. which conc-ludes: "Asbestos is too important in our technology and economy for ~ts essential use to be stopped. Hut, because nf the known serious effects of uncontrolled inhalation o.f ashestos mineral~ in industry. and uncertainty as l" the ~hape and character nf the d ...e-msponse curve in man, it would h( highly im- JOHN L. MYERS, Marketing Manager for the Calidria Asbestos Group in Union Carbide's Metals Div., received his B.S. Degree in Chemical Engineering from Purdue University in 1951. Joining Union Carbide that same year, he served in the Nuclear Division until1966, when he became a Research Engineer in the asbestos group. He was promoted to his present position in 1970. VoL. 47, No. 611, DECEMBER 1975 FMSI 05862 ly, the plastics industry uses primarily chrysotile asbestos and, in most products, the fibers are -locked-in to prevent airborne contamination. Although asbestos dust levels are generally lower than expected, industry continues to expend large amounts of time and money to further improve the quality of the workplace. Although the general public is not currently in danger, occupational controls are required to prevent future environmental rontamination. Chrysotile asbestos is an important and necessary raw material, vital to the nation's safety and economy; and, with proper control, it can he used safely and in compUance with government regulations. Medical, scientific, government, and industrial personnel must continue to work closely together to establish reasonable exposure limits, provide safe work areas, and eliminate any possibility of public endangerment. 0 References (I) Enterline, P. E. and Henderson, V.. Arch. Environ. Health, 27, 312 (Nov. 1973) . (2) Wagner. J. C., Ann. Occup. Hyg., 15, 61 (1972). (3) 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. 3. (4) Hammond E. C. and Selikoff, I. J., "Relation Of Cigarette Smoking To 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- dustr. Med., JO, 180 (1973) . (6) "Asbestos," National Safety News (Oct. 9, 1973) . (7) "National Emission Standards for Hazardous Air Pollutants," Federal Register, J8, No. 66, 8820 (April 6, 1973). (8) "Protecting the Asbestos Worker," Booklet No. IOID37, The Asbestos Information Association/North America, p 5. (9) Selikoff, I. J., lndustr. Medicine, J9, No. 4, 21 (April 1970) . (10) "Standard for Exposure to Asbestos Dust," Federal Register, J7, No. 110, 11320 aune 7, 1972). (II) Bayer, S. G., et al, "Equipment and Procedures for Mounting Millipore Filters and Counting Asbestos Fibres by Phase-Contrast Microscopy," Bureau of Occup. Safety and Health, U.S. Dept. of Health, Edu- cation, &: Welfare (Feb. 1969). (12) "Asbestos Health Question Per- plexes Experts," Chem. Eng. News, 18 (Dec. 10, 1973). (13) Myers, J. L., "Calidria Asbestos Pel- lets," ASBESTOS (Oct. 1971). VoL. 47, No. 611, DECEMBER 1975 Asbestos Information Association North America 1660 LStreet, N. W. Washington, D. C. 20036 FMSI 05863