What to know First, you can find OSHA’s Asbestos Standard, 29 CFR 1910.1001 here.  OSHA’s Construction standard for Asbestos, 29 CFR 1926.1101 is found here. In his 1986 Cummings Award lecture¹, former Assistant Secretary of Labor for Occupational Safety and Health in the Ford administration (1975-1977), Morton Corn first discussed documentation for asbestos by the American Conference of Governmental Industrial Hygienists in 1962: “The present threshold limit relates to the prevention of asbestosis. It was recommended by Dreesen, et al.² (in 1938) after study of 541 employees in three asbestos textile plants using chrysotile. Only three doubtful cases of pneumoconiosis were found in those exposed to dust concentrations under 5 mppcf (millions of particles per cubic foot), whereas numerous well marked cases were found above 5 mppcf. Counts were from impinger-collected samples in ethyl alcohol and distilled water. Both fibrous and non-fibrous particles were counted, but the latter greatly predominated. While chemical analysis of collected samples of airborne dust corresponded to those of settled dust samples, it is believed that dust counts of particulates by conventional methods can be expected to give only an indirect measure of the risk of asbestosis because of the great relative importance of long fibers.”³ From 1938 through the 1940s, ‘50s and half of the ‘60s, the accepted asbestos standard was based upon the 1938 Dreesen study, which, in turn used impingers to estimate particulate in terms of mppcf, i.e. millions of particles per cubic foot. In 1965, the Annuals of the New York Academy of Science published a 766-page document titled Biological Effects of Asbestos ⁴ By this time, a careful review of the Dreesen study found problems with the methodology. Three years later, in 1968, the British Occupational Hygiene Society (BOHS) published their standard for asbestos that included risk levels based on x-ray changes ^{5, 6}. Then, in 1970, the William-Steiger Act was law and OSHA was born. The next year, the 1971 ACGIH Documentation of Threshold Limit Values included this passage: “A conference on the biological effects of asbestos in 1965 called attention to the very real probability that the 5 mppcf (millions of particles per cubic foot) limit recommended by Dreeson is inadequate to give complete working-lifetime protection against all forms of asbestos. Medical data on which the limits had been based were inadequate; more than half of the asbestos workers studied were under 30 years of age and thus provided an insufficient exposure time for asbestosis to develop. Of the 105 workers exposed to less than 5 mppcf, 82 had worked less than 5 years; 101 less than 10 years; only 4 had more than 10 years exposure. Seven of the 36 workers exposed to 5.0-9.9 mppcf had asbestosis; 3 of 50 workers exposed to 10-19.9 mppcf for less than 5 years had asbestosis. “Moreover, it was a ‘point-in-time’ study; many of the ill were missing and the dead uncounted, hence not considered in the over-all evaluation of the limit.⁷.” In that 1986 lecture, Professor Corn noted, “the recommended guideline of 5 mppcf (million particles per cubic foot–which was roughly associated with an estimated equivalent exposure of 30 fibers/cc)⁸ –which had stood for 33 years without critical reappraisal in the U.S.  Then, the 1965 New York Conference and the 1968 BOHS recommended standard prompted (a) reappraisal⁹)” Thus, from 1938 until 1969, the recommended threshold limit value was 5 million particles per cubic foot. This corresponded with approximately 30 fibers per cc. In 1970, with the advent of the William-Steiger Act, the asbestos threshold limit value dropped to 2 mppcf, or approximately 12 fibers/cc. In 1971, OSHA did two things regarding the asbestos standard: (1) it decided to replace the old impinger/mppcf protocol with the membrane filter phase contrast microscopy technique, and, (2) it proposed a new, much lower standard for asbestos exposure: 5 fibers/cc. In the lecture, Morton Corn included a table of U.S. Asbestos Standards over the years, showing the 1971 proposal (5 f/cc), the 1971 Emergency Time-Weighted Average level of 2 fibers/cc (with a 15-minute Short Term Exposure Limit of 10 fibers/cc). Interestingly, the EPA, on March 31, 1971 listed asbestos as a hazardous air pollutant and carcinogen. The EPA also included all forms of asbestos in this category, including chrysotile, amosite and crocidolite. In 1975 OSHA published a notice of proposed rulemaking (40 FEDERAL REGISTER 47652) to revise the standard since “sufficient medical and scientific evidence has been accumulated to warrant the designation of asbestos as a human carcinogen ¹⁰” and proposed a permissible exposure limit to asbestos of 0.5 f/cc (15 minute STEL of 5 f/cc). After legal challenges, the 1976 proposed limit was 2 f/cc (STEL of 10 f/cc). That same year NIOSH recommended 0.1 f/cc (0.5f/cc for a Short Term Exposure Limit). Seven years later, in 1983 OSHA issued a Emergency Temporary Standard of 0.5 f/cc ¹¹ But on March 7, 1984, that Emergency Temporary Standard of 0.5 f/cc, issued on Nov 4, 1983, was held to be invalid by the U.S. Circuit Court of Appeals for the Fifth Circuit. The next month, OSHA issued a proposed standard of 0.5 or 0.2 fibers/cc. Two years later, on June 20, 1986, OSHA issued final rules on the 8-hour Time-Weighted Average asbestos exposure from 2 f/cc to 0.2 fibers/cc.¹² Two years after that, on Sep 14, 1988, OSHA added an amendment to the final rule by adding a 15-minute excursion limit of 1.0 fiber/cc average over a sampling period of 30 minutes.¹³ During this time period, entities such as the AFL-CIO, the Building and Construction Trades Department (BCTD) of the AFL-CIO and the Asbestos Information Association challenged various provisions of the OSHA standard. On December 20, 1989, OSHA removed a ban on spraying of asbestos-containing materials and changed the regulatory text to clarify when construction employers must resume periodic monitoring.¹⁴. Shortly after that, on Feb 27, 1990, OSHA banned smoking in workplaces where asbestos may be found and added a requirement that employees working in asbestos-regulated areas comprehend warning signs and labels.¹⁵) On July 20, 1990, reflecting pressure from industry, OSHA issued a clarification on the exemption for ‘small-scale, short duration operations.”¹⁶ Two years later, on June 9, 1992, OSHA deleted non-asbestiform tremolite, anthophyllite and actinolite from the asbestos regulations ¹⁷ On August 10, 1994, the permissible exposure limit for asbestos was officially lowered to 0.1 fiber/cc. OSHA included this statement on their site: “The 0.1 f/cc level leaves a remaining significant risk. However, as discussed below, and in earlier documents, OSHA believes this is the practical lower limit of feasibility for measuring asbestos levels reliably. However, the work practices and engineering controls specified. . .for specific operations and required respirator use will in OSHA’s view further reduce the risk.” “OSHA has always considered that a working lifetime risk of death of over 1 per 1000 from occupational causes is significant. This has been consistently upheld by the courts. See the recent discussion in the cadmium preamble 57 FR 42102, 42204 and the earlier asbestos preambles. “OSHA believes that compliance with these final amendments to reduce the PEL (permissible exposure limit) to 0.1 f/cc as a time-weighted average measured over 8 hours will further reduce a significant health risk which existed after imposing a 0.2 f/cc PEL. OSHA’s risk assessment accompanying the 1986 standard showed that lowering the TWA PEL from 2 f/cc to 0.2 f/cc reduces the asbestos cancer mortality risk from lifetime exposure from 64 deaths per 1,000 workers to 7 deaths per 1,000 workers. OSHA estimated that the incidence of asbestosis would be 5 cases per 1,000 workers exposed for a working lifetime under the TWA PEL of 0.2 f/cc. Counterpart risk figures for 20 years of exposure are excess cancer risks of 4.5 per 1,000 workers and an estimated asbestosis incidence of 2 cases per 1,000 workers ¹⁸ The critical passage in OSHA’s statement regarding the lowering of the Permissible Exposure Limit for asbestos is this one: “OSHA’s risk assessment also showed that reducing exposures to 0.1 f/cc would reduce excess cancer risk to 3.4 per 1,000 workers and a 20 year exposure risk to 2.3 per 1,000 workers. OSHA concludes therefore that reducing the exposure limit to 0.1 f/cc will further reduce significant risk.”  (c) Legis Corp 2025. All rights reserved. NOTE: To request the full document with end notes, use the Contact Form on this website and ask for “Asb History doc 1.”