# CRITERIA DOCUMENT: RECOMMENDATIONS FOR AN OCCUPATIONAL EXPOSURE STANDARD FOR ASBESTOS
recommends that worker exposure to asbestos dust in the workplace be controlled by requiring compliance with the following sections. Control of worker exposure to the limits stated will prevent asbestosis and more adequately guard against asbestos-induced neoplasms. The standard is amenable to techniques that are valid, reproducible, and available to industry and governmental agencies. It will be subject to review and will be revised as necessary. publication, the present emergency standard for exposure to asbestos dust (29 CFR 1910.93a) shall be in effect. This period is believed necessary to permit installation of necessary engineering controls.
Medical surveillance is required, except where a variance from the medical requirements of this proposed standard have been granted, for all workers who are exposed to asbestos as part of their work environment.
For purposes of this requirement the term "exposed to asbestos" will be interpreted as referring to time-weighted average exposures above 1 fiber/ cc or peak exposures above 5 fibers/cc. The major objective of such surveillance will be to ensure proper medical management of individuals who show evidence of reaction to past dust exposures, either due to excessive exposures or unusual susceptibility. Medical management may range from recommendations as to job placement, improved work practices, cessation of smoking, to specific therapy for asbestos-related disease or its com*plications. Medical surveillance cannot be a guide to adequacy of current controls when environmental data and medical examinations only cover recent work experience because of the prolonged latent period required for the development of asbestosis and neoplasms.
Required components of a medical surveillance program include periodic measurements of pulmonary function (forced vital capacity (FVC)), and forced expiratory volume for one second (FEV^), and periodic chest roentgenograms (postero-anterior 14 x 17 inches). Additional medical requirement components include a history to describe smoking habits and details on past exposures to asbestos and other dusts and to determine presence or absence of pulmonary, cardiovascular, and gastrointestinal symptoms, and a physical examination, with special attention to pulmonary rales, clubbing of fingers, and other signs related to cardiopulmonary systems. (ii)
The employer shall provide for maintenance and laundering of the soiled protective clothing, which shall be stored, transported and disposed of in sealed non-reusable containers marked "Asbestos-Con taminated Clothing" in easy-to-read letters.
(Hi) Protective clothing shall be vacuumed before removal.
Clothes shall not be cleaned by blowing dust from the clothing or shaking.
(iv) If laundering is to be done by a private contractor, the employer shall inform the contractor of the potentially harmful effects of exposure to asbestos dust and of safe practices required in the laundering of the asbestos-soiled work clothes.
(v) Resin-impregnated paper or similar protective clothing can be substituted for fabric type of clothing.

# (vi)
It is recommended that in highly contaminated operations (such as insulation and textiles) provisions be made for separate change rooms.
Each employee exposed to asbestos shall be apprised of all hazards, relevant symptoms, and proper conditions and precautions concerning use or exposure. Each exposed worker shall be informed of the information which is applicable to a specific product or material containing 5% or more asbestos (see Appendix III for details of information required).
The information shall be kept on file and readily accessible to the worker at all places of employment where asbestos materials are manu factured or used in unit processes and operations. It is recommended, but not required, that this information be provided for asbestos pro cesses and operations where the asbestos content is less than 5%.
Information as specified in Appendix III shall be recorded on U. S. Department of Labor Form 0SHA-20, "Material Safety Data Sheet", (see page X-3 and X-4), or a similar form approved by the Occupational Safety and Health Administration, U. S. Department of Labor.
Employers will be required- to maintain records of environmental exposure to asbestos based upon the following environmental sampling and recordkeeping schedule. Personal exposure samples will be collected at least annually by specific maximum-risk work operations from a number of employees. The first sampling period will be completed within 180 days of the date of this standard. These selected samples will be collected and evaluated as both time-weighted and peak concentration values. The personal sampling regime shall be on a quarterly basis for maximum-risk work areas under the following conditions:
(a) The environmental levels are in excess of the standard.
(b) There are other conditions existing that necessitate the requesting of a variance from the Department of Labor.
Records of the type of respiratory protection in use during the quarterly sampling schedule must also be maintained. The recommended standard is designed primarily to prevent asbestosis.
For other diseases associated with asbestos, there is insufficient information to establish a standard to prevent such diseases including asbestos-induced neoplasms by any all-inclusive limit other than one of zero. Nevertheless, a safety factor has been included in arriving at the concentration level that will reduce the total body burden and should more adequately guard against neoplasms.
Asbestos has been mined, milled, processed, and used for many years, and as a result, a number of workers have experienced significant accumulative exposure to asbestos dust over a working lifetime.
It has been recognized that biological monitoring (by periodic chest roentgenograms) and removal from further exposure after initiation of fibrosis, calcification or neoplasia will not absolutely prevent The construction industry has, in recent years, applied asbestos insulation materials by spraying, a method of application that generates more airborne asbestos fibers than older conventional methods. This technique at present utilizes only a small percentage of the total asbestos produced and its use is decreasing.
There are approximately 40,000 field insulation workers in the United States who are exposed to asbestos dust. The activities of these workers cause secondary exposures to an estimated three to five 2 million other building construction and shipyard workers.
Since the dust exposure to the individual worker is extremely variable and the number of asbestos workers at any one location is small, the primary and secondary asbestos dust exposures to all workers have never been satisfactorily estimated.
An estimated 50,000 workers are involved in the manufacture of asbestos-containing products. This figure does not include secondary manufacture of products which contain asbestos, such as electrical or thermal insulation, or products which include previously manufactured components containing asbestos.

# Early Historical Reports
The widespread use of asbestos fibers did not begin until the 2 last quarter of the nineteenth century.
With the increasing use of asbestos materials and increasing reports of asbestos related disease there developed concern over the role of these minerals as factors in human disease. Differentiation of the type of asbestos fiber was not made in most studies related to occupational exposure.
In the United States the exposures of greatest concern usually involve more than one type of fiber, although chrysotile predominates. To refine our knowledge of the biological actions of asbestos, it is imperative that the character of the exposure as to concentration, size, and type of fiber be known. At present, data of this complexity are scanty or often non-existent with respect to human exposure. Although a large percentage of the lungs of adult urban dwellers may be found to contain ferruginous bodies (depending on the method of examination), the significance of this is as yet unknown.
"Ferruginous bodies" is a more descriptive term. This and other aspects of the biologic effects of asbestos are well documented in the Annals of the New York Academy of Science.

# III-5
The core fibers have not been systematically identified to indicate how many are asbestos bodies, and there are little data bearing on possible health effects associated with the low concentrations of fibers found in ambient air.
An abnormality, occurring with unusually greater frequency in populations exposed to inhalation of asbestos fiber, is that of localized thickening, or plaques, of the pleura with or without calcification of the plaques. The role of the asbestos fiber in this manifestation is not clear.
The medical aspects of exposure to asbestos and the development of the occupational disease, asbestosis, are characterized by:
(1) A pattern of roentgenographic changes consistent with diffuse interstitial fibrosis of variable degree and, at times, pleural changes of fibrosis and calcification.
(2) Clinical changes including fine rales and finger clubbing.
These may be present or absent in any individual case.
(3) Physiological changes consistent with a lung disorder.
(4) A known history of occupational exposure to airborne asbestos dust. In general, a considerable time lapse between inhalation of the dust and appearance of changes as determined by X-ray.  Neoplasms, such as mesothelioma, may occur without radiological evidence of asbestosis at exposure levels lower than those required for prevention of radiologically evident asbestosis. This may be of particular importance when consideration is given to short-term, high levels of exposure, and may result in the development of meso thelioma before or after completion of a normal span of work either in or out of the asbestos industry. This is illustrated by several case studies, including two cases of malignant mesothelioma, one a "family" and the other a "neighborhood" 26 case.
In another "family" case, a woman washed the overalls of her three daughters at home; all three daughters worked for an asbestos company with possible heavy exposures to asbestos.

# III-9
The time lapse between onset of exposure and mesothelioma in 344 deaths among asbestos insulation workers was studied. Meso thelioma developed after a longer lapse of time from onset of exposure to asbestos than was the case in the development of asbestosis (Table  asbestosis, but that in most cases of mesothelioma that he had seen, the occurrence of asbestosis was not found. He postulated that the difference being the long periods of exposure required to produce asbestosis, while mesothelioma could occur long after a short intensive exposure. The 27 cases of mesothelioma in children under 19 years of age indicates the latent time period for develofpment of mesothelioma i may be shorter than first estimated.^9 on Fifteen casesJU of pleural mesothelioma associated with occupational exposure were reported in Australia. The relationship between the mesothelioma development and asbestos was based upon occupational histories and finding of asbestos bodies in the tissue. In some of these cases, the relationship to occupational exposure could not be developed with any degree of certainty, but included patients whose exposure was as short as six months. No patient was regarded clinically or radiologically as suffering from asbestosis; one person had pleural plaques that were radiologically visible.
Stumphiusbetween 1962 and 1968, found 25 cases of mesothelioma on Walcheren Island. Of these cases, 22 had been employed in the shipyard trades. Stumphius noted that the shipyard employed about 3000 men. This would result in a rate of mesothelioma of approximately 100 per 100,000 males per year. He also noted that the rate for Dutch provinces with heavy industry is 1.0 per 100,000 per y e a r .^ In the same study, examination of sputum from 277 shipyard workers showed that 60% had asbestos bodies. The frequency varied from 39% of those with no obvious exposure to 100% among those with slight but definite asbestos exposure. did produce in rats malignant pulmonary tumors of several types from exposure at very high doses (ca. 22,000 fibers/cc 86 mg/m^) of chrysotile asbestos that had been hammemilled to an increase in cobalt of 145%; nickel, 82%; and chromium, 34%.

# III-12
Differences in animal responses to "harsh" and "soft" chrysotile asbestos were seen by Smith al.^: granulomatous and fibrous pleural adhesions were thicker, and pleural mesotheliomas appeared more rapidly in response to harsh chrysotile. (Harsh chrysotile was characterized as appearing in thicker bundles and was hydrophobic whereas the soft chrysotile was hydrophilic).
There are no experimental animal dose-response data that can be used in estimating a work place air standard for asbestos.
Contributions to Occupational Exposure Standards from Animal Studies.
Of possible value in estimating occupational exposure limits are data regarding the relative disease-producing potency of the various forms and types of asbestos. (1) Fiber length and bundle size. The relation between length of fibers and of fibers to motes (nonfibrous particles) and asbestos induced disease has been one of continuing experimental inquiry.
Gardner and Cummings'^ and Gardner^ found that longer fibers appeared to have a greater fibrogenic effect, although fibrosis developed in animals exposed to dusts which were composed of but one to 1.5 percent fibers. The high exposure concentration of 100 mppcf (ca. 3,600 fibers/cc) makes any decision on the relative potency of fibers vs. motes virtually impossible; however, when animals were exposed to short-fiber asbestos dust, although the type and rate of tissue reaction

# III-14
were essentially the same, the extent of involvement was very much less than that of longer fibers. Inasmuch as exposure concentrations in these comparable studies were about the same, the conclusion can reasonably be made that longer fibers are more fibrogenic, but that the motes are not without fibrogenic potential.
In experiments with rabbits, King, Clegg, and Rae^~- using Rhodesian chrysotile fibers averaging 2.5 ;jm and 15 ;am in length, concluded that the shorter fibers produced generalized interstitial fibrosis, whereas the longer fibers produced nodular lesions. This finding was not confirmed by one of the investigators (King) in another animal species.^ Later repetition of the investigations, with "fine" chrysotile and amosite (85% and 82.6% respectively, less than 1 pa in length) by
Wagner^O yielded definite fibrosis with both dusts, thus confirming the original work of Gardner that short fibers or motes have fibrogenic potential.
This experimental work has significance for industrial air standards in indicating the need to support additional research on the "greater than 5 pm in length" specific requirement and the more general relation of fiber length to cancer induction, which has never been determined experimentally.
(2) Cytotoxicity. Both chrysotile and crocidolite were found to be markedly toxic to guinea pig macrophages in vitro.^ The fibrous fraction showed a high, and the particulate, a moderate toxicity, thus providing evidence in conformity with the relative biologic potencies of fibrous and nonfibrous forms found in in vivo studies.

# III-15
(3) Hemolytic Activity. In a similar effort to discover the initial stages of biologic activity of asbestos, and in particular to account for the iron-staining character of asbestos bodies, the hemolytic action of four asbestos types was determined. Whereas chrysotile proved to be potently hemolytic, crocidolite, amosite and anthophyllite were either completely inactive or only weakly.^ No attempt was made, however, to correlate the greater hemolytic activity of chrysotile with the ironstaining intensity of its asbestos bodies relative to those from other asbestos forms.
(4) Asbestos Hydrocarbons. As chrysotile proved to be most adsorptive of iron, so was it most adsorptive of benzpyrene; compared with 100% adsorption for chrysotile, crocidolite and amosite absorbed from solution 40% and 10% r e s p e c t i v e l y .^ On this basis, chrysotile should prove the most potent cocarcinogen of the three forms if its action is mediated through exogenous benzpyrene. This has not been demonstrated as yet in humans. A 10% desorption from chrysotile by serum in three days was demonstrated,^ a condition considered an essential first step in hydrocarbon carcinogenesis. In respect to asbestos bodies, it should be noted that "ferruginous bodies" produced in guinea pigs in response to other fibrous material, fine fibrous glass and ceramic aluminum silicate were identical in fine structure to that of asbestos b odies,^ thus rendering firm diagnostic decisions difficult in cases of multiexposures to different fibrogenic fibers in the electron and.light microscopic range. assumes that the fiber content of the dust is about 10% and he states that this is equivalent to about 12 fibers/cc. c ; - 7 Wright-' pointed out that others have noted the striking differences in the health experiences of workers in mines and mills as compared to other workers, specifically in comparison to insulation operations, but that he felt the question was still unresolved. In contrast to populations exposed to mixed environments, those engaged in the mining and milling of asbestos fibers showed no augmented frequency of b ronchogenic cancer.
Selikoff, ^ however, indicated that McDonald's "heavily exposed" group had 5 times as much lung cancer as the "lightly exposed" workers. Furthermore, lung cancer among insulation workers was found to be about 7 times greater than expected compared to the general non-exposed population.^ A non-exposed group was not reported by McDonald.A lthough it has been suggested that the risks associated with asbestos exposure may be less in mining than in industrial operations, additional study will be necessary to confirm if such is true, based upon the comparison made by S e l i k o f f .I

# II-19
Consideration must be given to McDonald's analysis of levels of exposure of 12 fibers/cc. At this level, he assumes that some degree of asbestosis may occur. The mathematical assumption made to arrive at this environmental level leaves a great deal to question, even without attempting to relate this information to the asbestos industry in general. Two primary considerations lack the evidence necessary to make general comparisons of these data with other reported work:
the assumption as stated by McDonald that the fiber content of the dust is 10%, and the method used to convert from mppcf to fibers/cc is not explained in the paper. The authors conclude that: "If asbestosis is to be prevented, airborne asbestos dust must be stringently controlled in the working environment.
From these data a TLV of 3 mppcf would provide inadequate protection and the proposed 2 mppcf may not be substantiated."

# III-21
Thus, considerable evidence exists indicating that the prevention or reduction of the occurrence of asbestosis among workers requires that the concentration of asbestos fibers to which they are exposed be reduced.
There is at this time, however, only scant correlation of epidemiological data with environmental exposure data upon which a definitive standard can be established. exposure that may be related to these two cases. If even in actual practice, levels were found to be 10 times those found by the investigators, it would substantiate the low levels of exposure recommended in this standard. The time interval for sanding as compared to tile installation must be small, and, if this is true, then, in fact, any level found would be very low if based on a time-weighted average exposure. This increases the weight of consideration that must be given to this possibly exposed occupational group and the relationship of these low exposures to asbestos to the development of disease.
Consideration must also be given related to the effect that may The individual sample high (  an index of exposure must be selected which, as nearly as possible, relates to the predominant biologic activity and dose-response of the size spectrum of fibers most commonly encountered. It is assumed for the present that the factor of safety associated with the standard will allow for differences in the size spectrum of respirable fibers that may be encountered.
The British, in evaluating respirable chrysotile fiber exposures in relation to the ongoing epidemiologic studies in the textile industry and for the basis of a standard for chrysotile, established as an index of 62 exposure, fibers greater than 5 micrometers in length.
A substantial amount of information on the biologic effects of asbestos has, and is, being obtained using this parameter of exposure measurement. A review of the research in Britain, with concurrence on the rationale involved, made it prudent that we use the same definition of index-of-exposure on which to base criteria for standards. These criteria should be re-evaluated when,
(1) more definitive information on the biologic response of asbestos including the agent(s) and dose-response data on different lengths of fiber is
V--2
available, (2) the spectrum of fiber lengths encountered in industry by types of asbestos and operations is ascertained, and (3) more precise epidemiologic data are developed.
To prevent fibrosis and excessive rates of neoplasia, such as meso thelioma, respiratory cancer, and gastrointestinal cancer, a standard for asbestos dust should be based on a concept of dose-response that includes not only the factor of fiber count times years of exposure but also that for total asbestos dust fibers retained over a number of years.
Thus, the effect after several decades of a one-time acute dose of limited duration which overwhelms the clearing mechanism, and is retained in the lungs, may be as harmful as the cumulative effect of lower daily doses of exposure over many years of work.

# V-3
The first standard for controlling exposure to asbestos dust was "1. As long as there is any airborne chrysotile dust in the work environment there may be some small risk to health. Nevertheless, it should be realized that exposure up to certain limits can be tolerated for a lifetime without incurring undue risks.
"2. The committee believes that a proper and reasonable objective would be to reduce the risk of contracting asbestosis to 1 percent of those who have a lifetime's exposure to the dust. By 'asbestosis'
V-5
this committee means the earliest demonstrable effects on the lungs due to asbestos.
"It is probable that the risk of being affected to the extent of having such early clinical signs will be less than 1 percent for 3 3 an accumulated exposure of 100 fiber years per cm or 2 fibers/cm 3 3 for 50 years, 4 fibers per cm for 25 years or 10 fibers per cm for 10 years. 3 per cm greater than 5 ^um in length as determined with the standard membrane filter method. Any other method can be used provided it is accompanied by appropriate evidence relating its results to those which would have been obtained with the standard membrane filter method. "5. When it is necessary to work intermittently in a 'high dust' area an approved mask should be worn, provided that the concentration 3 is no more than 50 fibers per cm a higher standard of respiratory protection should be provided such as a.pressure-fed breathing apparatus.

# V-6
"Additional Recommendations "1. It is recommended that where practicable an up-to-date employ ment record card be kept of every person which indicates, every calendar quarter, the category or categories in which he or she has been employed and in which he or she is recommended to work. "If asbestosis is to be prevented, airborne asbestos dust must be stringently controlled in the working environment. From these data a TLV of 3 mppcf would provide inadequate protection and the proposed 2 mppcf may not be substantiated."
Gee and Bouhuys,^^ in December, 1971, pointed out that on the basis of "reasonable probability," decisions must be made to control exposure to asbestos rather than from a precise definition of dose-response relation ship, and "the present threshold limit value for asbestos should be lowered far below some recent proposal." The 1971 ACGIH tentative threshold limit value is 5 fibers/ml y 5 ^m in length. Both are higher than the British standard of 2 fibers/cc by at least a factor of 1.5 times.

# V-9
The number of studies that have collected both environmental and medical data and with a significant number of exposed workers is not sufficient to establish a meaningful standard based upon firm scientific data. The requirement to protect the worker exposed to asbestos is defined in a number of studies outlined in this document. The general recognition of the increasing number of cases of asbestosis, bronchogenic cancer, and mesothelioma indicates the urgent need to develop a standard at the present time.
NIOSH recognizes that these data are fragmentary and, as a result, a safety factor must be included in any standard considered. On this basis the research that did include both environmental and medical data, or where a standard or limit had been proposed, was given a careful and detailed study to determine its particular contribution to the development of a national standard. contracting asbestosis to less than 1% of those who have a lifetime exposure to the dust. For such workers, who may possibly work for 50 years, the long-term average concentration to which they are exposed would need to be less than 2 fibers/cm . For others, who will be exposed to asbestos dust in air for shorter periods, the long-term average concentration need not be so low, as long as their exposure will amount to less than 100 fiber-years/cm It is recognized that the British standard is based upon data not as precise as desired, but it does offer a mechanism for com parison with the ACGIH TLV and after three years of use no change has been recommended. The British standard was primarily based upon a study of 290 men employed for 10 years or longer between 1933-1966 in an asbestos textile mill. The environmental dust concentrations to which different workers had been exposed were estimated to have varied 3 from 1 to 27 fibers/cm . The risk-exposure relationships were developed based upon basal rales and X-ray changes. In this study, basal rales were considered the key symptom since all workers exhibiting X-ray changes also exhibited basal rales.
In reviewing the values on the basis of the 100 fiber-years/cm proposed by the British Hygiene Standards Committee, the following comparisons can be made between the British Standard and the Emergency U. S. Standard. Each standard is normalized to 100 fiber-years to account for differences in the working lifetime of the average asbestos worker.
The Emergency U. S. Standard is based upon the ACGIH TLV which, in turn, 68 is based upon an exposure time of 30 years to 5 fibers/ml> 5 um in length , V-ll and the British, 50 years of exposure at 2 fibers/cm > 5 um in length.
In summary: U. S. Emergency British ACGIH 2 fibers/cc 5 fibers/ml Fiberyrs/cc 100 150
The validity of this type of comparison has already been questioned in this document, i.e., the "K" factor used to change ACGIH impinger 61>64 data to fiber counts. However, on this basis, data suggest that the ACGIH value is higher than the British value.
In addition to consideration of the British data, the comparison of British and ACGIH data suggests that the 30-year exposure value for a U. S. Standard should be about 3 fibers/cc 5 pm in length in order to assure that less than 1% of the workers exposed are at risk of developing the earliest clinical signs of asbestosis.
However, additional consideration must be given to the concepts of carcinogenesis as they relate to the determination of a standard for asbestos exposure. Any carcinogen (initiator) must be assumed, until otherwise proven, to have discrete, dose-dependent, irreversible and additive effects to cells that are transmissible to the cell progeny.
Thus, initiation of malignancy following single small exposures to asbestos is possible, but of a low probability. With frequent or chronic exposure and a low dose-rate, the probability of initiation of malignancy is increased. Yet, even under optimal conditions of cell proliferation (in the presence of promotors) these malignant

# transformations do not lead to instantaneous cancer, but remain insidious for a number of years (latent).
In protracted exposure, some of the total accumulated exposure is (c) The environmental samples were expressly collected in many cases for control purposes rather than for research and, as a result, meaningful evaluations cannot be made.

# Summary of the Basis for the Recommended Standard

# (d)
There is a lack of data to define with any degree of precision the threshold of development of neoplasms resulting from exposure to asbestos and the relationship of the latent period between exposure and development of neoplasms.
The standard recommended in this document is similar to the standard adopted by Her Majesty's Factory Inspectorate in 1 9 6 9^ (still in effect as of December 29, 1971), and more stringent than the recent U. S.
Emergency Standard. It is felt to be feasible technologically for the control of the exposure to the worker and effective biologically for protection of the worker against asbestos-induced diseases.
Considerations of carcinogenesis indicated the need for a measure of prudence. As a result of this rationale, a factor was added to reduce the time-weighted average exposure to 2.C) fibers/cc> 5 um. A ceiling value of 10.0 fibers/cc> 5 um that was not to be exceeded was included to reduce the possibility of the short-term heavy exposures to asbestos that have been reported to cause mesothelioma. In addition, this should reduce the likelihood of diseases (malignant and non-malignant) resulting from exposures in excess of 30 years or with very long latent periods. "IV. Part V, controlling manufacturing sources, is changed to require an emission standard of 2 fibers per cubic centimeter and no visible emissions. While some testimony indicated the difficulty in measuring compliance with a numerical emission standard, overall the evidence establishes both the need (protection against the great proportion of invisible fiber) and the ease of measurement of such a criterion. A "no visible emission" standard ha? been added to the numerical standard to simplify enforcemeat against exceptionally dirty emission sources. A grace period, until June 30, 1972, has been added to permit acquisition of the necessary control equipment to attain the emission standard."

# The proposed national emission standard for asbestos was published in the Federal
This air quality standard is, as it should be, more restrictive that an occupational standard due to differences in exposure time.
This proposed occupational standard would seem to be compatible with the proposed emission standard and each should complement the other in the control of asbestos exposure.

# VI-3
In the study of asbestosis conducted by Dreessen et al. midget impinger count data were used as an estimate of dust exposure. All of the dust particles seen, both grains and fibers, were counted since too few fibers were seen to give an accurate measurement. The resulting count concentration was a measure of overall dust levels rather than a specific measurement of the asbestos concentration. This method was satisfactory at that time since exposures were massive and the control measures installed to reduce overall dust levels also reduced the asbestos dust levels.
As dust levels were reduced, it became necessary to measure the biologically appropriate attribute of the dust cloud. At equal levels overall dustiness, the concentration of asbestos could vary considerably from textile manufacture (75-85%) to insulation (5-15%). Furthermore, if the limit were lowered below the 5 mppcf used previously and dust counts taken by the impinger technique, it would be necessary to consider the effect of background dust, which could be as high as 1 mppcf.
A number of methods for measurement of asbestos dust concentrations have been used in the NIOSH epidemiological study of the asbestos product Fibers longer than 5 jim in length are counted in preference to counting all fibers seen in order to minimize observer/microscope resolving power variability. Furthermore, the British define a "fibre" as a particle, "of length between 5 jim and 100 pm and having a length-to-breadth ratio of at least 3:1, observed by transmitted light by means of a microscope 62 at a magnification of approximately 500X."
Although the British have refrained from standardizing on a single method of measurement, recent measurements have been performed by a method essentially identical to the fiber-count method described in detail below, and the British hygiene standards for use with their 62 asbestos regulations are stated in these terms.

# Principles of Sampling
A dust sampling procedure must be designed so that samples of actual dust concentrations are collected accurately and consistently.
The results of the analysis of these samples will reflect, realistically , the concentrations of dust at the place and time of sampling.
In order to collect a sample representative of airborne dust, which is likely to enter the subject's respiratory system, it is necessary to position a collection apparatus near the nose and mouth of the subject or in his "breathing zone" The concentration of dust in the air to which a worker is exposed will vary, depending upon the nature of the operation and upon the type of work performed by the operator and the position of the operator relative to the source of the dust. The amount of dust inhaled by a worker can vary daily, seasonally, and with the weather. In order to obtain representative samples of workers' exposures, it is necessary to collect samples under varying conditions of weather, on different days, and at different times during a shift.
The percentage of working time spent on different tasks will affect the concentration of dust the worker inhales since the different tasks usually result in exposure to different concentrations. The percentage can be determined from work schedules and by observation of work routines.
The dally average weighted exposure can be determined by using the following formula:
(Hours X conc. task A) + (Hours X conc. task B) + etc. 8 HOUts (or actual hours worked)
The concentration of any air contaminant resulting from an industrial operation also varies with time. Therefore, a longer sampling time will better approximate the actual average.
With the following recommended sampling procedure, it is possible to collect samples at the workers' breathing zones for periods from 4 to 8 hours, thus permitting the evaluation of average exposures for a half or full 8~hour shift-a desirable and recommended procedure. Furthermore, dust exposures of a more normal work pattern result from the use of personal samplers. In evaluating daily exposures, samples should be collected as near as possible to workers' breathing zones.

# Collecting Sample
The method recommended in this report for taking samples and counting fibers is based on a modification of the membrane filter method described by Edwards and Lynch. ^V

# III-3
The sample should be collected on a 37-millimeter Millipore type AA- filter mounted in an open-face filter holder. The holder should be fastened to the worker's lapel and air drawn through the filter by means of a battery-powered personal sampler pump similar to those approved by NIOSH under the provisions of 30 CFR 74. The filters are contained in plastic filter holders and are supported on pads which also aid in controlling the distribution of air through the filter.
To yield a more uniform sample deposit, the filter-holder face-caps should be removed. Sampling flow rates from 1.0 liter per minute (1pm) up to the maximum flow rate of the personal sampler pump (usually not over 2.5 1pm) and sampling time from 15 minutes to eight hours are acceptable provided the following restraints are considered: The following conclusions may be drawn from this analysis:
(1) The short-term limit should be for a period of at least 15 minutes and preferably 30 minutes.
(2) The 2.0 fiber/cc limit may be evaluated over periods of from 90 to 480 minutes.
A8 many fields as required to yield at least 100 fibers should be counted. In general the minimum number of fields should be 20 and the maximum 1 0 0 .

# Mounting Sample
The mounting medium used in this method is prepared by dissolving 0.05 g of membrane filter per ml of 1:1 solution of dimethyl phthalate VIII-5
and diethyl oxalate. The index of refraction of the medium thus prepared is ND = 1.47.
To prepare a sample for microscopic examination, a drop of the mounting medium is placed on a freshly cleaned, standard (25 mm X 75 mm), microscopic slide. A wedge-shaped piece with arc length of about 1 cm is excised from the filter with a scalpel and forceps and placed dust-side-up on the drop of mounting solution. A No. 1-1/2 coverslip, carefully cleaned with lens tissue, is placed over the filter wedge. Slight pressure on the coverslip achieves contact between it and the mounting medium. The sample may be examined as 800 as the mount is transparent. The optical homogeneity of the resulting mount is nearly perfect, with only a slight background granularity under phase contrast, which disappears within one day. The sample should be counted within two days after mounting.

# Evaluation
The filter samples mounted in the manner previously described are evaluated in terms of the concentration of asbestos fibers greater than 5 }im in length. A microscope equipped with phase-contrast optics and a 4-mm "high-dry" achromatic objective is suitable for this deter mination. 10X eyepieces, one of which contains a Porton or other suitable reticle at the level of the field-limiting diaphragm, should be used. The left half of the Porton reticle field serves to define the counting area of the field. Twenty fields located at random on the sample are counted and total asbestos fibers longer than 5 jim are recorded. Any particle having an aspect ratio of three or greater is considered a fiber.

# VIII-6
The following formulae are used to determine the number of fibers/ml:
(1) Filter area (mm2) = K Field area (rnm^)
(2) Average net count X K = fibers/ml Air volume sampled (ml)
For example, assume the following: area of the filter used was 855 mm2 > counting area of one field under the Porton reticle was 0.005 mm2 average net count per field of 20 fields was 10 fibers; and sample was collected at 2 liters per minute for 90 minutes: Then: 855mm2 = 171,000 (K) 0.005 mm2 10 fibers x 171,000 = 9.5 fibers/ml 2,000 ml/min x 90 min

# Calibration of Personal Sampler
The accuracy of an analysis can be no greater than the accuracy of the volume of air which is measured. Therefore, the accurate calibration of a sampling device is essential to the correct interpretation of an instru ment's indication. The frequency of calibration is somewhat dependent on the use, care, and handling to which the pump is subjected. Pumps should be calibrated if they have been subjected to misuse or if they have just been repaired or received from a manufacturer. If hard usage is given the instrument, more frequent calibration may be necessary.
Ordinarily, pumps should be calibrated in the laboratory both before they are used in the field and after they have been used to collect a large number of field samples. The accuracy of calibration is dependent on the type of instrument used as a reference. The choice of calibra tion instrument will depend largely upon where the calibration is to be performed. For laboratory testing, a 1-liter burette or wet-test meter should be used. In the field, a rotameter is the most convenient VIII-7 instrument used. The actual set-up will be the same for all of these instruments. The calibration instrument will be connected in sequence to the filter unit which will be followed by the personal sampler pump.
In this way, the calibration instrument will be at atmospheric pressure.
 ? Connections between units can be made using the same type of tubing used in the personal sampling unit. Each pump must be calibrated separately for each type of filter used, if, for example, it has been decided to use a filter with a different pore size. The burette should be set up so that the flow is toward the narrow end of the unit.
Care must be exercised in the assembly procedure to insure adequate seals at the joints and that the length of connecting tubing be kept at a minimum. Calibration should be done under the same conditions of pressure, temperature and density as will be encountered. The rotameter should be used only in the field as a check if the diaphragm or piston pumps are not equipped with puls>ation dampeners. The pulsating flow resulting from these type pumps causes the rotameter to give results which are not as accurate as that obtained with a burette or wet-test meter. Calibration can be accomplished with any of the other standard calibrating instruments, such as spirometer, Marriott*s bottle, or drygas meter. The burette and wet-test meter were selected because of their accuracy, availability, and ease of operation.

# VIII-8
IX.

# APPENDIX II NUMERICAL HAZARD RATING SYSTEM
Thii numerical hazard ratings given to products for each category of hazard shall be in accordance with the following criteria. Figure 2 graphically illustrates the hazard identification system.
Health hazards shall be rated as follows:
The health hazard rating of a material shall be determined by evaluating the potential for exposure and the relative toxicity of the most toxic ingredient of a compound or mixture. For this evaluation, the tolowing relative toxicity criteria- for absorbed or exposure dose will be used: protective equipment, such as self-contained breathing apparatus or a hose mask with blower, and impervious clothing. This rating includes:  Corrosive Material. Acids, alkali or other material that will cause severe damage to living tissue or to other material it contacts.
Commonly
Water Reactivity Hazard (Use No Water). Any material that may be a hazard because of its specific reactivity with water. Dimensions of the symbol and L A P I warning combination shall be optional but cf such size and location as to be readily visible and legible.

# IX-6
The symbol nnu warn in-; shall be applied by stencil mp;, painting, printing, lithographing, \viih fadc-rf:si!".:inil materials.

# IX-7
X.

# APPENDIX III MATERIAL SAFETY DATA SHEET
The following items of information which are applicable to a specific product or material containing 5% or more of asbestos shall be provided in the appropriate section of the Material Safety Data Sheet or approved form. If a specific item of information is Inapplicable (i.e. flash point) initials "n.a." not applicable should be Inserted.                      1 -Personal Communication Dr. Irving Selikoff, January, 1971.

# TABLE XXVIII
Lapsed period from onset of exposure in 344 deaths among employees of an asbestos insulation factory, employed at some time in 1941-1945 and followed to 1970.
contaminated absorbants, etc.
(ix) Section VIII. Special Protection Information.
(A) Requirements for personal protective equipment, such as respirators, eye protection and protective clothing, and ventilation such as local ex haust (at site of product use or application), general, or other special types.
(x) Section IX. Special Precautions.
(A) Any other general precautionary information such as personal protective equipment for exposure to the thermal decomposition products listed in Section VI, and to particulates formed by abrading a dry coating, such as by a power sanding disc.
(xi) The signature of the responsible person filling out the data sheet, his address, and the date on which it is filled out.
(xii) The NFPA 704M numerical hazard ratings as defined in section (c) (5) following. The entry shall be made immediately to the right of the heading "Material Safety Data Sheet" at the top of the page and within a diamond symbol preprinted on the forms.
-Not applicable