Document 06YMBd3X3qkDdX4pdprdox0Zn

DEPARTMENT OF HEALTH, EDUCATION. AND WELFARE PUBLIC HEALTH SERVICE CENTER FOR DISEASE CONTROL August 8, 1975 NATIONAL INSTIHUl'f? f OR OCCUPATIONAL SAFCTY `AND HEALTH ------ - . 5600 FISHERS LANE ROCKVILLEvMARVLANO 20SS2 ,/ Dear Colleague: This communication is intended to alert you to recently gathered informa1tion Indicating a potential health hazard for persons exposed to asbestos during the servicing of motor vehicle brake and clutch assemblies. On July 21, 1975, the National Institite for Occupational Safety and Health convened a meeting of government and university scientists, industry representatives, and labor union officials to discuss the present state of knowledge with respect to this problem. Data was presented by Investigators from the Mount Siani School of Medicine in New York City indicating that workers engaged in the maintenance and repair of automobile and truck brake linings are exposed to potentially hazardous levels of airborne asbestos dust. Specific brake servicing operations studied included blow-out of automobile drum brake assemblies, grinding of used truck brake linings, and bevelling of new truck brake linings. Average peak asbestos air concentra tions for these three activities based on personal samples taken within ten feet of the operator were, respectively, 10.5, 3.75, and 37.3 fibers (>5 microns in length) per ml. An analysis of samples of brake drum dust revealed that'almost all of the asbestos fibers found were shorter than 0.4 microns in length. - Previous studies of the extent of asbestos emissions from automobile brake lining wear showed that only a very small fraction of the original asbestos content of the brake lining is found in brake drum dust (Ref. 1-3). It was presumed that this is due to thermal degradation of the fibers during braking. The present findings Indicate that enough asbestos is preserved to produce . significant exposures during certain brake servicing procedures. The full extent of asbestos-related disease in brake servicing personnel is not known at present because this, particular occupational group has not been studied systematically up to now. However, a review of the scientific literature on the association between asbestos exposure and ' mesothellal tumors of the pleura and peritoneum has revealed at least four cases of these rare tumors in persons who were employed in jobs involving automobile brake servicing (Ref 4-6) . VJ V (L} FMSI 06259 Page 2 For your information and guidance, we are enclosing pertinent references, estimates of the population at risk, a N10SH interim recommendation for brake and clutch servicing procedures, and a copy of the Department of Labor standard covering exposure to asbestos in the work place. _ The environmental studies of brake lining servicing operations outlined above together with observations of mesothelial tumors in persons so employed affirms the necessity for instituting and maintaining recommended control measures in this Industry so that the health hazards of asbestos . are minimized. Enclosures Office of Occupational Health Surveillance and Biometrics J ' . ' I FMSI 06260 REFERENCES 1. Lynch, J.R.: Brake Lining Decomposition Products. J Aif Pollution Control Assoc, 18;824-26, 1968 ` 2. Hickish, D.E. and Knight, K.L.: Exposure to Asbestos During Brake Maintenance. Ann Occup Hyg, 13s17--21, 1970 ," 3. Jacko, M.G. and DuCharme, R.T.; Brake Emissions: Emission Measure ments from Brake and Clutch Linings from Selected Sources. EPA --. Report 68-04-0020, 1973 4. Newhouse, M.L. and Thompson, H.: Mesothelioma of Pleura and Peritoneum Following Exposure to Asbestos in the London Area. Brit J Ind Med, 22:261-69, 1?65 5. McDonald, A.D. et al.: Epidemiology of Primary Malignant Mesothelial Tumors in Canada. Cancer, 26:914-19, 1970 6. Greenberg, M. and Lloyd Davies, T.A.: Mesothelioma Register 1967 1968. Brit J Ind Med, 31:91-104, 1974 I FMSI 06261 ESTIMATES OF THE WORKFORCE POTENTIALLY EXPOSED TO ASBESTOS " IN THE MANUFACTURING AND SERVICING OF BRAKE LININGS Ap CLUTCHES Auto Mechanics Garage Workers Manufacture (original and rebuilding) TOTAL 833,535 6^,679 / 6,657 907,871 SOURCE: ,Adapted from 1972 Census of Manufacturers, 1972 County Business^Patterns, and Census of Population: 1970 Occupation by Industry (all are'Department of Commerce, Census Bureau publications) . I. i'Jlt: \ J FMSI 06262  . RECOMMENDED (INTERIM) PROCEDURES FOR * ASBESTOS BRAKE AND CLUTCH SERVICING f ' * ' '" ^ The National Institute for Occupational Safety and Health (NIOSH) has research underway concerning dust exposures during brake and "clutch servicing. Due to preliminary data demonstrating significant asbestos exposures during presently used brake and clutch servicing techniques. NIOSH has reviewed t alternate techniques whereby asbestos exposures are reduced. The following are interim procedures recommended by NIOSH to, minimize dust exposures. 1. If possible, an area shall be designated for all brake and clutch repairs. Entrances into this area shall be posted with an asbestos exposure warning sign as follows: . *___ Asbestos '. ' Dust Hazard Avoid Breathing Dust Wear Assigned Protective Equipment - Do- Not Remain in Area Unless Your Work Requires It Breathing Asbestos Dust May Cause Asbestosis and Cancer 2. During brake servicing, an air purifying respirator, either single use ( or with replaceable particulate fllter(s), as approved by the Mining Enforcement and Safety Administration (formerly Bureau of Mines) or NIOSH, shall be worn during all procedures starting with--ther removal of the wheels and including Reassembly. During manual clutch servicing, such a respirator shall be worn during removal and cleaning of the clutch, pressure plate and housing assembly and during instal lation of the new clutch assembly. , 3. Dust 6hall first be cleaned from brake drums, brake backing plates, * brake assemblies and clutch assemblies using an Industrial type vacuum cleaner equipped with a high efficiency filter system (>99% efficiency for 0.3 pm diameter aerosols). After vacuum cleaning, any remaining dust shall be removed using a rag soaked in water and wrung until nearly dry. Under no circumstances shall compressed air or dry brushing be used for cleaning. 4. During arcing and riveting operations, an approved respirator, as described in (2) above, shall be worn. 'Grinding' (arcing) machines shall be provided with lotal exhaust ventilation such that worker exposures are maintained at least below the 1976 OSHA asbestos standard (29 CFR 1910.1001).* At a minimum, the dustbag of the arcing machine shall be removed and replaced with the hose of the, high efficiency industrial vacuum described in (3) above. > , I * . $ FMSI 06263  * ? 2 - - 5* Industrial vacuum cleaner bags containing asbestos dust,and cloths used for wiping brake and clutch assemblies shall be sealed in plastic `bags and labeled with the following warning label printed in letters of sufficient size and contrast to be readily visible and legible; t . -.... ' Caution ,i .' : Contains Asbestos Fibers < ' Avoid Breathing Dust . .Breathing Asbestos Dust May Cause Asbestosls and Cancer All asbestos waste shall be disposed of in accordance with the OSHA asbestos regulation, 29 CFR 1910.1001(h). During removal of vacuum bags, an approved respirator, as described in (2) above, shall be* worn. f -- ' i_ 6, All floor cleaning in areas where brakes and clutches are repaired shall be done with the high efficiency industrial vacuum cleaner as described in (3) above. Grinding (arcing) machines shall also be cleaned with Buch a vacuum cleaner and.any remaining dust wiped with a damp cloth'. An approved respirator, as described in (2) above, shall be used during this cleaning. 7. Although adherence to the above procedures ^should minimize any contamination of work clothing, it is required that the appropriate portions of the OSHA regulations on asbestos (29 CFR 1910.1001(d), (3 and 4)) concerning special clothing, change rooms, etc* be followed. :-3 NOTE: Strict adherence to the above procedures should minimize exposures to mechanics during brake and clutch servicing. These are interim recom- ^ mendationa and are subject to revision pending results of ongoing NI0SH . research. s -' * Section 1910.1001 of the Code of Federal Regulations was formerly Section 1910.93a. This change was noted in the Federal Register, May 28, 1975. . ' -T ! J Prepared By Division of Field Studies and Clinical Investigations National Znstltute for Occupational Safety and Health , Cincinnati, Ohio I \ t` w '* m . ' ; \ FWISI 06264 Recommended Procedures for Sampling and Counting Asbestos Fibers Procedures for llie Evaluation of Occupational Exposures to Airborne Asbestos i Joint AIHA-ACGIH Aerosol Hazards Evaluation Committee ibrous asbestos has been FIDENTIFIED as the causative agent of asbestosis and has been associated with an increased cancer incidence. The American Conference of Governmental Industrial Hy gienists (ACGIH) has established (1974) a Threshold Limit Value (TLV) for asbestos of 5 fibers greater than 5 micrometers in length per milliliter of air. A TLV footnote specifics the determination shall be made by the membrane filter method at 400 X to 450 X magnification and with phase contrast illumination. These procedures define a standard of sampling and of processing the collected samples in order to evaluate occu pational exposure to asbestos fibers. Sampling Airborne samples of asbestos must be collected on membrane filters which retain at the surface essentially all of the particles in excess of 0.5 fim in diameter. The filter must be rendered transparent by the mount ing medium. The filter should be packed in a scaled holder which is capable of being readily opened for sampling purposes and of being rescaled after the sample has been collected. The filter must be fully exposed during sampling. (Recommended filters and filter holders arc listed under Supplies). The filter must be practically dust-free, with an average background count of less than 25 Reprints of this article are available for purchase from either the American Industrial Hygiene Association, 66 South Miller Road, Akron, Ohio 44313 or the American Conference of Governmental Industrial Hygienists, P.O. Box 1937, Cincinnati, Ohio 43201, The cost la $1.00 per copy. fibers per square centimeter. At least 2% to 4% of the filters intended for collecting samples should be set aside to determine the background count. (Sec Counting and Cal culations sections). In addition, the filter resistance should not exceed 3 mm of mer cury when filtering air at the rate of 0.3 liters per minute (1pm) per square centimeter of filter. When collecting the sample, care must be taken to prevent dust from falling pr from being projected onto the open filter. This may be accomplished by pointing the filter head downward. A guard or shroud should be attached to the filter holder to further protect the open filter from contamination as well as optimize uniform deposition on the filter. Its diameter should be about the same as the holder so that it can bc"attachcd tightly to it and it should project at least Wi times the filter diameter in front of it. A protective device is particularly important if the filter head is to rest on contaminated clothing. (See Figure 1.) The filter holder may be stored for a limit of six months once it is resealed. The sample should not be too dense, since samples in which particles overlap must be rejected as uncountable. Similarly, a large enough volume of air should be sampled so that there arc sufficient numbers of fibers in each field. Experience indicates that more than 150 particles per field, including nonfibrous background, may interfere with counting the sample. It is desirable that there be no more than 10 fibers per field. Two or three samples should be collected at each sampling location. The results should I l; I i * if l; jj l; f f \ t 83 y-iV ____Li_ % FMSI 06265 84 Figure 1. Diagram of shroud for membrane fil ler holder. The shroud may be constructed from a plastic bottle by cutting off the neck and drilling a hole in the bottom. To use, push the filter holder through the hole and reach in through the top to remove the holder cap. To remove the holder, re place the cap and push the filter holder forward through the hole. . be averaged to obtain the fiber concentra tion. Breathing zone samples should reflect the worker's entire normal work day. They must be collected as close to the worker's nose and over as long a time period as possible. Calibrated battery powered per sonal pumps (see Appendix III, Pump Cali bration) are satisfactory air movers. They can be worn by the worker and supported at the belt by means of a clip. The sam pling head, which can be pinned to the Col lar, is connected to the pump by flexible tubing. Such pumps can be operated continu ously for about eight hours and recharged overnight. If a 37-mm filter is used to collect the sample, the pump should be adjusted to sam ple between 1 and 2 liters per minute. The volume of air sampled should be adjusted so that an optimum density of dust is col lected on the filter. Since the dust concentra tion is not known before sampling, the op timal sampling period must be determined by trial and error. It is suggested that, unicss experience indicates otherwise, the first sam ple should be collected from 20 liters of air, the second from 40 and the third from 80 February, 1975 liters. If a filter other than 37-mm is used, the volume of air sampled should be altered in direct proportion to the open filter area. Samples collected during short- periods of exposure should be collected at a high flow rate and if necessary, for the entire exposure period. In all eases the count should be adjusted with regard to time, so that the exposure is expressed as an 8-hour timeweighted average exposure. For compliance evaluations with short term exposures, 37 mm filters samples should be collected for 15 minutes at a minimum of 2 1pm. Sample Preparation A solution one-to-one by volume of di methyl phthalatc and diethyl oxylate in which has been dissolved 50 milligrams of membrane filter material per milliliter of solution is the preferred counting medium. The chemicals used to prepare the medium should be examined microscopically to be certain that they are dust free. The fiber material to be dissolved should not be marked and should have a maximum back ground count of 25 fibers per square centi meter of filter. The counting medium may be stored in a wide-mouthed Wheaton Bal sam bottle and should be applied with a glass rod. The counting medium has a re fractive index of 1.461 at 25C. The me dium should be made in small quantities since it has a 6 month shelf life. Asbestos fibers are counted on wedge shaped sections cut from the filter. The wedge should be reasonably sized so that it can be mounted on a 25 x 75 mm (1x3 inch) glass microscope slide. The slide should be cleaned of dust before it is used. A drop or two of counting medium is placed on the slide and the filter wedge is placed dust side up on top of the medium. The wedge is covered by a No. \V% covcrslip. Care must be taken while lowering the coverslip to avoid trapping air under it. Air bub bles may be forced out by exerting slight pressure on the cover slip with a pencil eraser. Extreme care must be taken to avoid % FMSI 06266 American huliislriul llynit'iif A.\.\oiiiiliiiii Jotnliiil too much pressure, since this causes distor tion and stretching in the filter. The wedge is usually cleared within 15 minutes; however, a residual background granularity may be noted. This will disap pear within a day. Counts must be com pleted within two days since there is a tendency for fiber migration and crystal growth. The prepared medium should be checked periodically for a background count. (See Counting and Calculations sections.) An alternate medium may be used when the samples must be counted immediately. It is prepared in the same manner as the preferred viscous medium, except that the added membrane filter is omitted. Since this medium is much less viscous it should be stored in narrow-mouthed bottles. This me dium is applied with a glass dropper after the filter wedge has been placed dust side up on the slide. However, a drop should be placed on the slide adjacent to but not on top of each corner of the wedge. This me dium acts very rapidly and the No. 1V4 covcrglass should be lowered within a min ute. Slides made up with this "alternate medium" are ready for counting within five minutes and the count must be completed within two hours after preparation. Filters which have been used to collect samples and which have been rescaled in a holder should be removed only in a clean environment. They should not be held with the fingers. They may be held with tweezers and cut with cither a scalpel or scissors. Bottles containing media must be tightly closed except during use. All bottles, tools used for handling and cutting filters, and containers used for storing tools must be thoroughly cleaned and dried. Tweezers, scissors, scalpels, etc. should be set aside for this purpose exclusively. Although slides and covcrslips arc purchased pre-clcancd, they should be wiped lightly with clean lens tisuc to remove traces of dust. Do not at tempt to reuse slides or covcrslips. Microscope A microscope equipped with a phase con- 85 trasl substage condenser, it 4 mm "high dry" phase-contrast objective (40 X to 45 X) and a 10 X eyepiece is used to count the sample. It should have either a pre-focused built-in illuminator supplied with an iris diaphragm or be lighted by a separate bright illuminatorflat mirror combination. If a separate illu minator is used it should be equipped with a condensing lens, iris diaphragm, and means for adjusting both the illuminator level and the distance between the condensing lens and the bulb. Zoom microscopes may be used for counting asbestos fibers, provided that the total magnification is within the 400-450 X range. The illuminator should be equipped with an adjustable constant voltage transformer. Both the microscope condenser and stage require close adjustment and both should be rack and pinion mounted. The stage must move along two perpendicular axes in a horizontal plane, while the condenser must move up and down in a vertical plane. Lighting must be adjusted for optimum bal ance. The Kohler method of illumination is recommended. (See Appendix I for pro cedures required to establish Kohler illu minator.) The counting field is defined by a reticle mounted at the level of the field-limiting di aphragm in the 10 X eyepiece. The Porton reticle (Figure 2) is recommended. However, any reticle which contains markings which, in addition to outlining an area of about 0.005 square millimeters, as determined by i* > ooo * 9 0 0 t # t n Figure 2. Porton reticle. % FMSI 06267 86 the combination of eyepiece and objective, and which defines linear distances that may serve as measuring aids, is satisfactory. The 'reticle must be' calibrated prior to use and ' recalibrated each time it is removed from the microscope eyepiece or when the micro scope tube length or intcrpupillary distance is changed. Zoom microscopes must be re calibrated each time the zoom position is changed. (Sec Appendix II for recommended calibration procedures.) Counting A fiber is defined as a particle whose length is at least three times greater than its diameter. All fibers longer than 5 /Am within the area delineated by the reticle, or which enter it from cither of two adjacent sides, arc counted. Fibers entering the area from cither of the other two sides, /.<?., those not arbitrarily chosen as "counting" sides arc not counted, nor fibers in excess of 5 /im in diameter. Touching fibers, i.e., one of whose ends touch another fiber regardless of the resulting angle, arc considered as one. Fibers that cross each other arc counted in dividually. Fibers that pass through the de lineated area arc counted provided that they cross at least one of the arbitrarily chosen "counting" sides. (Sec Figure 3.) Fiber length should be determined by measuring against standards such as a circle or a space defined by markings on the cali brated reticle. If the fiber is curved or wavy the total length should be estimated by meas uring along the curve. Once sufficient ex perience has been gained in judging length, only fibers whose length or diameter arc in question need be measured. A routine for choosing counting fields must be selected so that fields arc not count ed more than once and that a representative fraction of the total filter area is viewed. A convenient procedure which may be used is to select a scries of microscope viewing fields along a radial line extending from the apex of the filter to the outer edge of the sample wedge. The viewing fields must be February, 1975 chosen without preference to a particular area and should be approximately equally spaced along the line. The first field should be located a little bit in from the point at which matter is deposited on the filter. If the required number of viewing fields can not be located on a single radial line, addi tional lines parallel to the first should be chosen. Preferably 100 fibers should be counted but all the fibers in 20 fields should be counted even if there are more than 100 fibers. The counting may be terminated after 100 fields have been searched even if 100 fibers have not been counted. Calculations The concentration of asbestos fibers in air can be expressed as: Asbestos Cone. Fibers x R Fields x Voi Figure 3. Illustration of fiber counting with a Porton reticle. The top and left side of the large box have been chosen as "counting sides". Circle 6 is 5 jitn in diameter. (A) Fiber A crosses the top of the box and is counted, therefore. One end of Fiber A] touches Fiber A and thus is considered as part of it and is not counted separately. (B) Fi ber I) is a bundle containing many spikes. It passes through the box crossing bottom and top. It is counted as one fiber. (C) Fiber C passes through the box but it crosses the right side and bollom. It is not counted. (D) Fiber D is entirely within the box and crosses over Fiber A. It is not part of Fiber A, therefore it is counted as a separate fiber. (E) Fiber E is less than 3 41m in length. It is not count ed. % FMSI 06268 American Industrial Hygiene Association Journal 87 where: the system except that if desired, neutral Fibers = total number of fibers counted density filters may be used to reduce the Fields = total number of fields counted light intensity. If the microscope is equipped r_ filtration area area of a counting field Vol = sampling rate (1pm) x time (min) with a built-in illuminator, proper iMumjnator positioning has already been accomplished and need not be of further concern. x 10* = sample volume in ml of air Since both the filtration area on the mem brane filter and the area of the counting field arc normally constant, the ratio of areas, R, is constant for the given conditions. To illustrate: Air is sampled at 1 liter/ minute for 50 minutes on a 37-mm mem brane filter (filtration area 855 mm2). A total of 60 fibers each longer than 5 (im are counted in 100 fields each 0.003 mm2 in area: ' Fix a mounted sample on the stage and rcchcck the alignment. Raise the substage condenser until it nearly touches the bottom of the slide. Turn on the illuminator and use the tilt controls to direct the light to the center of the mirror. Tilt the mirror, direct ing the beam upward into the stage con denser. Close the microscope substage iris and the illuminator iris. Use the illuminator focus control to focus the image of the fila ment on the bottom of the substage iris. The reflection of the iris may be viewed in !j 855 mm2 3 x 10-3 mm2 2.8 x 10s and the mirror by leaning over the microscope. After adjusting the illuminator condenser so that there is a sharp image of the filament on the substage iris, open it about halfway. Recheck proper position of the mirror and Asbestos Cone. = 2.8 x IQ3 x 60 Fibers______ i1m00 cFielidis x-I---*---10:-*-1-1-1--1-x 5e0n mi.n nun . . then put the objective in place and focus sharply on the sample. It may be necessary to open the substage iris during focusing. = 3-4 Fiber$/jjil After the sample is in focus, fully close Since the precision of this mctlibii is limited, the iris. Readjust the condenser height so the averaged results of the several samples that the edge of the iris leaves are in sharp should be reported to the nearest significant focus and there is a bright spot within the i figure. iris. Readjust the mirror to obtain maximum brightness. If the color around the iris is Appendix I > not uniform, rcchcck the illuminator tilt and Recommended Procedure for Establishing focus. If the color is uniform and maximum Kohler Illumination brightness has been achieved, open the field The microscope is set on a level surface iris until the blades just pass out of the field at a convenient height and in such position of view. that sighting through the eyepieces is possible The proper phase stop is inserted or ro without undue strain or discomfort. tated into place in the substage condenser. i The illuminator is placed directly in. front The phase objective is rotated into place. of and aligned with the microscope. If the The eyepiece is replaced with the phase ring illuminator is equipped with a coil filament centering telescope. The telescope is ad bulb, its iris should be ten inches from the justed for sighting. The location of the mirror. If a ribbon filament bulb is used, phase ring is observed through the telescope. the front of the filter holder should be at It may be adjusted by using the two rotating least seven inches from the mirror. Only shafts provided with the phase condenser. the plane surface of the mirror should be When the ring is centered it appears as a used. All filters should be removed from bright annular ring mounted on top of a } N V' % FMSl 06269 February, 1975 grey ring. The center is black. There should is related in terms of L units of length in . be no overlap of the bright ring into the accordance with the formula: center. When the phase stop is centered the tcleseopc is removed and the eyepiece is re placed. The microscope is now ready for use. D = Ly/IF where n is the diameter of the circle or the width of the space and N is the number of the circle, or space. Appendix II The unit L is determined by measurement. A stage micrometer is the primary ruler. Recommended Procedures for Any one or more of the definitive linear di Calibrating Reticle mensions may be measured. If the length The reticle must be slightly smaller in of the large rectangle is measured then L ; diameter than the eyepiece in which it is to equals I/200th of that value. i be used. It fits into the tube and is held in If the stage micrometer is marked in hun i place at the eyepiece focal point by spring dredths of millimeters the value of L is in | pressure. The focal point is marked by an hundredths of millimeters. If the left square j internal collar which prevents the reticle is used as a counting area, its area is equal , ! from passing further into the tube. Some to manufacturers locate the focal point just (100 x 0.01 L)2 mm2 j below the collar while others prefer a point The filtering area of a 37-mm filter is 855 j immediately above it. Thus it may be nec- mm2 and thus j cssary to insert the reticle between the lens | and the collar on one microscope and below I the collar on another. In either ease the n - 855 K L2 ' ; projected image of the reticle on the field If other areas arc used as counting fields j ' c must be clear and sharp. or other sized filters are used, the value of I./ | The reticle must project a constant count- R must be calculated for the individual con- i - | ing area as well as provide markings for dition. i sizing. Many types of reticles are satisfac- It is wise to prepare a chart showing each j tory. The Porton reticle illustrated in Figure linear dimension and area for ready reference " ] 2 is recommended. It outlines a large rec- while counting. \ tangle that fits easily within the field of : vision. The rectangle is divided into two Appendix III | \ equal squares. The left square is further ; divided into six rectangles. Each side of Pump Calibration j j j each square has a length equal to 100 L, Personal sampling pumps should be cali- j then the large rectangle is 200 L units long brated for flowrate frequently. They may be j j and the small ones 50 L units long and 33V6 calibrated against a primary meter such as t ] L units high. To the left of the left square a spirometer or againsta previously calibrat- I * is a scale which divides the side into 20 cd secondary standard such as a wet gas ; equal increments of 5 L units each. The -meter or dry gas meter. The train should be right square is divided horizontally in thirds arranged so that the pump is operating * ' corresponding to the small rectangles and against the same resistance it would normally vertically into a series of increasing spaces. operate against, and that the calibrating ' The distance between each vertical line and meter is at atmospheric pressure. Figure 4 the center of the large rectangle corresponds illustrates the recommended arrangement. to the diameter of a circle. Circles of sizes Air flow through (he filter may be limited ' 1 through 9 are located above and below the by both restricting the air flow to the pump j large rectangle. The diameter of each circle as well as by admitting'secondary air into } FMSl 06270 American Industrial Hygiene Association Journal KETSR Figure 4. Diagram of set-up for calibration of pump. the pump. Most personal pumps arc con structed with adjustment valves that permit both actions. Calibration should be repeated after each 24 to 36 hours of pump use. If the pump has not been used for a prolonged period of time it should be recalibrated. Temperature and altitude corrections should be made. Personal sampling pumps should not be used to such an extent that the batteries arc allowed to run down below normal operating voltage. Since battery life varies, it is wise to occasionally check the life of the battery by allowing the pump to run down to the first indicated change in voltage under timed simulated conditions. Supplies Filters ami Filter Holders Millipore Corp." Field Monitor filter hold ers preloaded with 37-nim Type AA filters, cither white plain (catalog #MAWP037A0) or gridded (#MAWG037AO) arc recom mended. These are sold with a guaranteed average particle background and can be used without additional background checks. It is less expensive to purchase unloaded field monitors (#MA13G037A0) to be loaded with plain or gridded filters pur chased separately in packages of 100 (#AAWP03700, and AAWG03700). The field monitor can then be reloaded after each use. However, it is necessary to care fully clean the empty monitor and to check the background count on filters in the re loaded monitor. 89 Type AA fillers can be used in any di ameter in any non-leaking open-type filter holder, as long as proper adjustment is made in the calculations for the change in filtering area, and periodic background checks arc made. Membrane filters of other types and man- ( ufacturcrs cannot be recommended at this ' time, either because they do not become optically clear in the mounting medium or because of excessive particle background. Personal Battery Powered Sampling Pumps (1) Casclla'' MK 11 or MK 111 Personal Sampler (2) MSA' Monitairc Sampler, Model G. (3) Bendix'1 VM 22 or Micronair Per sonal Sampler or C-l 15. Microscopes: Phase Equipped . (a) microscope body with a fine focus accuracy of 0.006 mm; (b) 10 X eyepiece; (c) mechanical stage; (d) illuminator (preferably built in and having provisions for adjusting light intensity); (c) 40 X to 45 X (0.65 N.A. at least) positive (bright field) phase-contrast objective; (f) annual ring condenser diaphragm (corresponding to the objective); and (g) phase ring centering telescope. (Note: Most manufacturers sell a basic body unit and built-in illumination system as a unit. Phase-contrast accessories can us ually be purchased as a kit consisting of 10 X, 40 X and 90 X phase objectives, a phase condenser containing appropriate an nular ring diaphragms, a phase ring center ing telescope, and a green filter. It is to the microscopist's advantage to purchase the kit.) A list of manufacturers of phase-contrast microscopes'' and reticles^ is given below to aid in selecting a proper instrument. * Millipore Corp,, Bedford, Man*. 071*0. * Willson Products Div., P.O. Box 622, Reading, Penna. i%03. C. F. Casclla A Co. ltd., KegeM House, Britannia 90 February,1973 ! Walk, London, N.l, England. E. Leitz Inc., Rocklclfth, N.X. 07647. \ <* Mine Safely Appliance Co., 201 Brnddock Avc,, Pitta- Nikon Inc., Instrument Division, Garden City, N.Y. | biirjih, 1`cnna. 1520H. 113.10. j 4 Bemlix--Nlil, P.O. Box 390, Fall River, Mass. 02722. Unitron Instrument Company, Microscope Sales Divl* ) * Buu&ch and Lomb, Scientific Instrument Division. sion, 66 Needham Street, Newton Highland, Mass. 02161. | 72624 Bausch Street,Rochester, N.Y. 14602. Carl Zeiss, 444 Fifth Avenue, New York, N.Y. 10016. i Olympus Microscopes, Micro Optics Company, 28163 ' Edmund Scientific Co., 701 Edsorp Building, Barring 1 Greenfield, Southfield, Mich.4R075. ton, N.J. 07007. j! American Optical Corporation, Reichert Products, Buf- BGI, Incorporated, 39 Guinan St., Waltham, Main. falo, N.Y. 14215. 02154. | Joint AIHA-ACGIH Aerosol Hazards Evaluation Committee AIHA .' ACGIH !I Morion Lippmann, Ph.D., Chairman ! J. LcRoy Balzer, Ph.D. Howard E. Ayer George Carson, Ph.D. Douglas K. Craig, Ph.D. Harry J. Eltinger Graham W. Gibbs, Ph.D. Murray Jacobson William C. Janes Geoffrey Knight William H. Krebs, Ph.D. Jeremiah R. Lynch Carl A. Mangold G. Major Eric B. Sansone, Ph.D. . Owen Moss Marvin Tillery Milton Scheinbaum Thomas F. Tomb Glen W. Sutton Russell W. VanHouten i Wesley R. VanPelt, Ph.D. Donald L. Webster I ( i i Industrial Hygiene Training in Israel j Medical and engineering students at Tel Aviv University will be ob- \ ligated in the future to undertake training in occupational safety, hygiene j and health to inspire them with an awareness of their obligations for the 1 maintenance of the health of the worker and for the prevention of ill j j effects from work on man. . j This has been made possible by the establishment in 1974 by the I Faculties of Medicine and Engineering of the University, in collaboration i | with the Ministry of Labor, of the National Insurance Institute and the } j Workers Health Insurance (Kupat-Holim) of a Center for Occupational t.t ; Safety, Hygiene and Health, with four major departments--Physiology of i Work and Rehabilitation, Occupational Toxicology, Occupational Hygiene, l j and Safety Engineering. It comes to fill long-standing gaps in the promo- j lion of safety and health of the working population in Israel and the j absence of training facilities for specialists in these fields. The new Center will immediately provide refresher courses for physicians and nurses, but curricula for the training of Occupational Toxicologists, Hygienists and Physiologists arc in preparation. Ultimately the Occupa- tional Health Physician will also be trained at the Center. Due to lack of suitable personnel in the country the Center is seeking to recruit specialists from abroad. % FMSI 06272 Telephone (201) 945-0440 FRICTION MATERIALS STANDARDS INSTITUTE, BERGEN MALL OFFICE CENTER E. 210 ROUTE 4 PARAMUS. N J. 07652 INC. February 23, 1977 Subject: Recommended Procedures for Reducing Asbestos Dust During Brake Servicing Gentlemen: As I'm sure you are aware, there have been questions raised concern ing exposure to asbestos dust during brake servicing. Actually, what applies to brake servicing might equally apply to clutch servic ing, except that ordinarily installers do not drill, cut or grind new clutch facings in the field. As a result of the concern expressed in several quarters, two committees and our Board of Directors reviewed the problem, and have endorsed the enclosed "Recommended Procedures for Reducing Asbestos Dust During Brake Servicing." It is felt that these are sound and workable procedures, and x*e suggest that your publication may wish to give them wider distri bution, either in a brief article on asbestos, or in a separate commentary on the subject. You are free to use these recommendations as you see fit. There is no copyright involved, and it is not necessary to give credit to the Institute. If you wish to give credit, you may. We believe that distribution of such information is in the best interests of all involved in the brake (and clutch) service business. If you have any questions, please let me know. Sincerely, FRICTION MATERIALS STANDARDS INSTITUTE EWD/lmc E. Ttf. Drislane Executive Director FMSI 06273 RECOMMENDED PROCEDURES FOR REDUCING ASBESTOS DUST DURING BRAKE SERVICING Because studies have indicated that exposure to excessive amounts of asbestos dust may be a potential health hazard, OSHA has set maximum limits of levels of airborne asbestos dust to which workers may be exposed. Since most automotive friction materials normally contain a sizable amount of asbestos, it is important that people who handle brake linings and clutch facings understand the nature of the problem and know the precautions to be taken. 1. Areas where brake work is done should be set aside if possible, and entrances should be posted with an asbestos exposure sign as follows: Asbestos Dust Hazard Avoid Breathing Dust Wear Assigned Protective Equipment Do Not Remain in Area Unless Your W.ork Requires It Breathing Asbestos Dust May Be Hazardous To Your Health 2. The amount of asbestos in the dust from brake lining wear is normally at an extremely low level because of chemical breakdown during use, and if machining of friction material does not take place, simple procedures will minimize exposure. During brake servicing, the mechanic snould wear an air purifying respirator, either a throwaway or one with replaceable particulate filter(s), as approved by the mining Enforcement and Safety Adminis tration or NIOSH. It should be worn during all procedures starting with the removal of the wheels and including reassembly. 3. During disassembly, all parts should be carefully placed on the floor to minimize the possibility of creating airborne dust. Dust should first be cleaned from the brake drums, brake backing plates and brake assemblies using an industrial type vacuum cleaner equipped with a high efficiency filter sys tem. After vacuum cleaning, any remaining dust should be removed by using a rag soaked in water and wrung until nearly dry. Under no circum stances should compressed air or dry brushing be used for cleaning. 4. Of extreme importance are the precautions which must be taken during machining of friction ma terial. This is the operation in brake servicing when exposure to asbestos dust is at its highest. In addi tion to the approved respirator, there must be local exhaust ventilation such that the worker exposures are maintained at least below the 1976 OSHA asbestos standards. If there is any question as to the efficiency of asbestos dust removal by the ma chine, the manufacturer should be contacted. 5. Industrial vacuum cleaner bags containing asbestos dust and cloths -used for wiping brake assemblies should be sealed in plastic bags and labeled with the following warning label printed in letters of sufficient size and contrast to be readily visible and legible: Caution Contains Asbestos Fibers Avoid Breathing Dust Breathing Asbestos Dust May Cause Serious Bodily Harm All asbestos waste should be disposed of in accord ance with the OSHA asbestos regulation. During removal of vacuum bags, an approved respirator, as described in (2) above should be worn. 6. All floor cleaning in areas where brakes are repaired . should be done with the high efficiency industrial vacuum cleaner as described in (3) above. Under no circumstances should dry sweeping take place. Grinding (arcing) machines should also be cleaned with such a vacuum cleaner and any remaining dust wiped with a damp cloth. An approved res pirator, as described previously should be used during this cleaning. 7. Although adherence to the above procedures should minimize any contamination of work clothing, it is necessary that the appropriate sections of the OSHA regulations on asbestos be followed when ceiling levels on asbestos dust exceed current stand ards. This could involve special clothing, change rooms, etc. At the very least the work clothes should not be taken home but should remain at work for industrial laundering. 8. Proper hygiene practices will help minimize ex posure to asbestos dust. Wash thoroughly before eating and do not eat in the work area. Remember, smoking is harmful to the hcnlth, and smoking coupled with breathing asbestos dust is extremely dangerous. CAUTION: DO NOT BREATHE ASBESTOS DUST FMSI 06274 V V ` -The Hazards off Asbestos ffor Brake Mechanics . > * BARRV CASTLEMAN, LUCILLE A. CAMAROTA, ALBERT J. FRITSCH, iiUiAiN MAZZOCCHI, and ROBERT G. CRAWLEY Asbestos is the generic name of a group of hydrated magnesium silicate mineral fibcr$. There are two groups of these minerals--serpentine (chrysotilc) and amphibole (amositc, crocidolitc, anthophyllite, trcmolitc, and actinolitc).. Ninety-five percent of the world's asbestos production is chrysotilc. Reports of epidemiologic and pathological studies (1--4) reveal that occupational exposure to commercial asbestos minerals enhances the likelihood of a number of diseases--asbestosis and cancers of the lung, pleura, peritoneum, larynx, and gastrointestinal tract. The time from onset of exposure to the time of clinically ap parent disease is usually more than 20 years. Cancer from asbestos is not limited to workers who handle the material. There arc also reports of pleural and peritoneal mesothelioma (tumors rarely seen in the general population) in persons with family, or neighborhood, or indirect occupational exposure to asbestos (4--7). . Mesothelioma was the cause of death of a man who had regularly sanded vinyl asbestos floor tile (8). Under simulated conditions of this man's work, a maximum asbestos dust concentration of 1,3 fibers per ml (fibers longer than 5 microns) was found in air samples passed through membrane filters worn by a person sanding vinyl asbestos (S). The type of asbestos now used in domestic floor tile is chrysotilc--the same as that used in brake friction materials, according to the Asbestos Information Association. A ease of mesothelioma in a brake mechanic has been reported (9). Clomntvitin! fritiluh niniefldU inetI In the United States for braking passenger cars and trucks contain an average composition of 50 percent chrysotilc by weight (10). Asbestos has been used for brake drum linings, disk pads, and clutch facings fob the past 50 years. Jacko and DuCharme (11) estimated that the United States annually uses 103 million pounds of asbestos for brake friction materials and 4.5 million pounds in automotive clutch friction materials. In 1968 Lynch reported that because of the heat of friction caused by braking, almost all of the asbestos in brake linings is transformed to a nonfibrous mineral, and a small fraction of asbestos escapes as free fiber (12). Jacko and co-workers determined that vehicles in this country emit 158,000 pounds of asbestos per year, of which 11.2 percent is retailed in the brake and dis posed of during service (13). Brake mechanics have low and intermittent exposure to asbestos. This exposure has been reported to be 0.79 fiber per ml time-weighted average (fibers longer than 5 microns), with peaks up to 7 fibers per ml when brake parts arc being cleaned (14). The standard method for removing dust from brake parts is to blow it out with a DAir. Castleman, an environmental engineer, was with the Center Jar Science in the Public Interest when this paper was prepared; he is now with the Maryland Public Interest Research Group. Dr. Erilsch is dirtclor of the Center for Science in the Public Interest. Ms. Camarota is an occupational health nurse, District oj Columbia Department of Human Resources. Ms. Ma^uahi was a research associate, Environmental Cancer Research Project, Environmental Sciences Laboratory, Mount Sinai School of Medicine, New York City. Mr. Cratvley is a Sanitarian, Ilnltimore County Department of Health. Tenrshe/t tet/tierii to Hurry Cattleman, Maryland Public Interest Research Group, 3110 New Alain Dining Hall, University of Ataryland, College Park, Aid. 20742. 2&4 frvt>1>C Ho*l.h ftaporU FMSt 06275 - ^compressed ;\ir hose. In 1970 several reports ( //-/<>') T described die levels of exposure of brake mechanics to * asbestos; alternative fiiction materials, and specific changes in brake repair practices which would reduce the levels of exposure. Baltimore and Washington Studies In December 1972, the llaltimore County Department of Health mailed a I-page mimeographed circular to about 130 establishments which provide brake repair service. These businesses included new car and truck dealerships, certified motor vehicle inspection stations, and other concerns advertising brake repair as a specialty. Some of the establishments initially con- tacicd hail cither gone out of business or replied that . they do not do brake repairs. The circular warned that inhalation of the dust from brake cleaning could cause serious diseases, including cancer, and advised vacuuming brakes of accumulated dust. Additional measures suggested were improved ventilation and the use of face masks ( W). Two student volunteers went to 100 of tiie places on the'mailing list 4 months later to ask shop managers what methods they were using in brake repair. A similar study was started in Washington, D.C., in August 1973. This work was conducted by the Center for Science in the Public Interest and the District of Columbia Department of Human Resources. Of 186 brake service establishments initially contacted, 120 were followed up. Several new methods were tried in ortlcr to improve the effectiveness of the warning. The warnin'; leaflet was more eye-catching and readable than the paragraph-form sheet used in Baltimore; the leaflets were handed out by an occupational health ' nurse to the mechanics themselves--none were mailed; and followup to ascertain the degree of effectiveness was conducted by the same nurse who interviewed the repair shop managers. The Washington study was also featured in a local television program at the time the leaflets were first handed out. ' hrrutivt Cjt totOMto r-r! wiJ Ik-*rr IX i rH "* ` i 0 r** k#**, r v**1 My M. 0 y*> 0 Yw VUj Urtjtl Ox oo**-r <4*m i W **..*. **, M ftywM) * is* <*k *1 tv<i \ A Wil k-* *. 0, 00 ,*l 4+* A* ' * is. a* * 90 M *< bO *>M*a y*i ^iT.TTri ( V Ww*<y * \;n Or.i >#*. " w ( MM _________ jh,Tr.:i| U.r* ..*, M < .> **!.> M k | **T k A| rn |HI|HUMm 1 ' ##**- ****** l ............ bl*Wl*Ni**'ill ttrmut % *'** i " *< **" tej DAAX fitPAJft WOfiK CAN BE HajanftuJ lOYCWt HEALTH />. IJlV To assure that students trained in brake repair by public vocational schools would learn proper methods, health officials met with appropriate school officials in both locations. At the time they were contacted, school officials in Baltimore anti Washington reported that the schools were leaching the "blow out" method of brake dust removal to the trainees. .' The standard met liorl of cleaning brakbs is "blowing out" with a compressed air hose. In Baltimore, 63 per cent (65 per I BO) of the brake repair establishments contacted were using this method at the lime they received the warning circulars. In Washington, the figure was 91 percent (110 of 120). Most of the managers and workers interviewed had never heard /iboul the ha/,anions potential of brake dust. Predict ably, the responses ranged from annoyance to apprecia tion. Of the 65 places in Baltimore initially blowing out brakes, 11 were using either vacuum or wet brushing methods at the lime of followup. Four others were still blowing out brakes, but had improved ventilation or provided- dust masks, or both, to reduce workers' ex posures. In Washington, only two establishments had changed to wet brushing, but nope were vacuuming brakes. Four others provided face masks. Interestingly, two others decided to change brake shoes in all brake repairs, thereby simplifying the problem of dust removal and reducing the mechanics' exposures. The degree of improvement, indexed by the percent-, age of establishments converting from blowing out brakes to safer techniques after a single warning, was 23 percent in Baltimore County and 7 percent in Washington. This disparity probably arises more from differences in the methods of the studies than from differences in the study groups. It may be critically important to approach manage ment at the outset in order to enlist the cooperation needed to implement any changes in practice. A mechanic who is approached directly with a warning may simply disregard it. The mechanic might reason that if the dust were really dangerous, there would be a law requiring the use of preferred methods in brake repair. And the employer, if not asked to participate from the beginning, may well conclude that he need not be concerned with the matter. The failure to involve management may be the main reason why the Washington study produced less gratifying results than the Baltimore study. Brake warning programs consisting merely of mailed warning notices require little manpower, compared to other health programs. Also, the effort to implement safe techniques in public vocational schools is lime well spent. Conclusion .* Over a 7-ycar period ending in 1976 (20,21), the U.S. standard for time-averaged exposure to asbestos will have been reduced from 5 million particles-per cubic May-Juna 1075, VoL 90, No. 3 3SS i i i / t t f I t 1 i FN1SI 06276 t-fooi <>f .iir to (iIhts por ml (lilicib ImijjiT lit.in ii *, microns)? lor asbestos textile plants, this mluciiim is '"s about 15-foKI 1 22). 1`resntt anti sehecluletl stamlai ds \ claim only to protect workers ai;ainst nshrstosis, the disease for which the dose-response relationship is most quantitatively known. The British standards for chrysotilc and amosite asbestos, which tire comparable to the asbestos standard scheduled to lake cl fee l in the United States in 1976, do not put port to provide protec tion against increased risk of cancer {23,21). Previously studied cohorts of asbestos workers were exposed to time-averaged concentrations greater than 2 fibers per ml (fibers longer than 5 microns). Current studies of cohorts with time-averaged exposure on the order of 1 fiber per ml (greater than 5 microns in length) may provide evidence of hazard at that level. In view of alarming preliminary findings of pulmonary fibrosis in such a cohort, the National Institute of Oc cupational Safety and Health has suggested to the Department of Labor that consideration be* given to further lowering of the`asbestos standard (25). The average brake mechanic is not aware of the potcr.iial hazard of ai; borne brake dust. Nor is he quick to change time-hardened habits when warned of dangers if he cannot feel their effects. Nonetheless, sub stantial reduction in asbestos exposures during brake repair can be achieved by simple changes in technique, with the use of equipment already available in most brake service establishments. In view of the tendency of the accumulating literature to reveal cancer induction from asbestos at progressive ly lower levels of exposure, mechanics should be ad vised not to blow out brake parts and to use instead methods which create less airborne dust. The manufac turers of automotive friction materials could easily at tach a clear hazard warning to every item sold. The limited success of both the Baltimore and Washington studies shows the limited efficacy of volun tary compliance with health warnings--the shop managers and the mechanics simply do not have the same regard for a warning that they have for a regula tion. The margin of safety, if any, provided by the current asbestos standards has been sharply criticized as insufficient (26). While it is advisable that brake mechanics at least be warned of the potential hazard of their work, it is also apparent that blowing out.brakes will be a common practice so long as health regulations permit it. References 7. Cooper, \V. C., ct al.: Asbestos--the need for and feasibility of air pollution controls. National Acadenty of Science*, Washington, D.C., 1971. . 2- Scliurr, l. J., Hammond, r. C., and Churg, J.: Mortality ex perience* of asbestos insulation worker*, Jn Proceeding* of the International Conference on Pneumoconiosis, Johannesburg, 1969, edited by li. A. Shapiro. Oxford University lVe*i, Capetown, South Africa, I97u, pp. 180--186. J. Stell, P. M., and McGill, T.: Asbestos and laryngeal carcinoma. L.imef 2; 4 If.- 41 7, Am; !!>, I9/.V _ /. NYwhmne, M. I... and lhnmpuMi, II ; MrmtUrlimiM ol the pleura and pet iloncuni following exp*.sun* t. asbestos in (he I .on* don area. Hr J 1ml Med 22; 261 -2<.9 fi. Lichen, j., and Pistawka, II : McmthiTimna ami asbestos ex posure. Arch Environ Health 1*1: 3VJ-563 (1907). 6. Wagner, J. 0., Slrggs, G. A ami Match.md, 1*.: Diffuse pleural mesothelioma and .`Mu-sins exposure in 111<* North Western Cape Province, Hr.| Iml Med I?: 230-271 (1900/. ^ ' 7, D.dtpien, I1., Dabbrrt, A. F., and llin/, l.: Epidemiologic der Picurainrsothriiom.v Vorlaufiger Herirht uber IIV F.dle aus drm Hamburger. Kauni lYax I'ncumnl 23: 347 -- S5H (1909). 5. Murphy, R. L-, cl al.: Floor tile installation as a source of ashestu* exposure. Am Rev Respir l)is 101: 370-380, October 1971. '' 9. Sullivan, R. J., anti Aihanassiadis, Y. C.: Preliminary air pnllu- lion survey of asbestos. Nadonal Air Pollution Control Ad ministration, Arm 09-27. RalcighfN.G., 1909, p. 32. JO, Harwood, C.: Asbestos air pollution from the wear of brake linings. Illinois Institute of Technology Research Institute. Chicago, April 1972. 11. Jaeko. M Cl., and DuCliarmc, R.T.: Brake emissions* emission measurements from brake and clutch linings from selected mobile *ourccs, Environmental Protection Agency Report 68-04-OO20. Ann Arbor, 1973. ' 12. Lynch, J.: [bake lining decomposition product*. J Air Pollut Control Assoc 18: 82-1--826 (1968). 7J. Jaeko, M. G. DuCharmc, R. T., and joiners, J. H.: Brake and . clutch emissions during vehicle operation. Paper presented at Society of Automotive Engineers Meeting,'Detroit, MayM973. 14. Hickish, D. E., and Knight, K. L.: Exposure to asbestos during brake maintenance. Ann Occup Hyg 13: 17 -- 21 (1970). 15. I latch, D.: Possible alternatives to asbestos as a friction material. Ann Occup Myg 13: 23 -- 29 (1970). 16. Knight, K. L-, and Hickish, D. ir; Investigations into alternative forms of control for dust generated during the cleaning of brake assemblies and drums. Attn Occup Hyg 13: 37--39 (1970). 17. Lee, G. L.: Removing dusts from brake assemblies during vehicle servicing--alternative cleaning methods. Ann Occup Hyg 13: 33-36 (1970). 75. Bentley, M. L.: Control of the use *>f asbestos-containing friction materials. Ann Occup. Hyg 13: 31--32 (1970). 19. U.S. Senate, Committee on Commerce: Toxic Substances Con trol Act of 1973. Hearings before the Environment Subcom mittee. Statement of H. Castlrm.m 93d Cong. U.S. Government Printing Office, Washington. D.C., 1973, pp. 117, 349--350. 20. Guenther, G. C.: Emergency standard for exposure to asbestos dust. Federal Register, vol. 36, No. 234, Dee. 7, 1971, pp. 23207-23208. ` 21. Guenther, G. C.: Standard for exposure to asbestos dust. Federal Register, vol. 37, No. 110, June 7, 1972, pp. 11318* 1 1322. 22. Lynch, J. R., Ayer, U. E., and Johnson. D. *L.: The in ' tcrrelntionship of selected asbestos exposure indices. Am Ind Hyg Assoc J 12: 598-601 (1970). 2.7. Hygiene standard for chrysotilc asl>e*u>* dust. Ann Occup Hyg . II; 47-49 (1968). 2-1. Hygiene standards for airborne atnositc asbestos dust. Ann Oc- cup Hyg 16: 1-5 (1973). 25. Key, M. M.: Reopening of asbestos standard. Memorandum to J. Slender, Assistant Secretary of Labor, Occupational Safety and I le.dlli Administration. Office of Technical Publications, National Institute for Occupational Safety and 1 lealth, Rockville, Md., Marsh 28, 1974. ' 2fi. Gee, U., ami Hoohuys, A.: Action ti\a*lexio. N EnglJ Med 285: 1317-1318, Dec. 2, 1971, 266 Public Health Report* FMSI 06277