It has come to my attention that expert testimony in support of disability claims based on employer negligence for workers exposed to operations involving asbestos have applied a threshold limit value (TLV) erroneously as a basis for negligence.
Over the period of 1946 to 1970, the American Conference of Governmental Industrial Hygienists (ACGIH) had determined that the air breathed by exposed workers should not exceed an average threshold limit value (TLV) of 5 million particles of asbestos per cubic foot of air.
This standard was based principally on the results of a study by Dr. Dreessen and others of dust conditions in six asbestos textile plants with material used being essentially all asbestos. This study was published as the 1938 Public Health Bulletin, No. 241, by the U.S. Public Health Service.
In the production of such products as pipe insulation, the material used was often composed of 15% asbestos and 85% other mineral content not conducive of the characteristic injurious action of asbestos. Sampling of air for its particulate concentration over that period was conducted by means of a so-called impinger technique, by which all particulates were collected in distilled water or alcohol-distilled water solution.
When the percentage of asbestos in the mineral combination used was 15%, this percentage of the total particulate concentration was, properly, taken as the asbestos particulate Concentration. A result of less than the 5 million asbestos particulates per cubic foot standard established compliance with the existing standard.
It is a matter of history that the concentration of asbestos fibers longer than 5 microns is a more accurate measure of the extent of the hazard than the particulate count. Also, over these last years, the acceptable fiber concentrations have become progressively lower. When a comparison is made of the particulate concentration corresponding to the fiber concentration, this decreasing fiber standard would indicate that the particulate standard, if still extant, would be much lower than the 5 million of the 1946-1970 period.
However, the standard during the period over which claimants were being
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