Document B5bVB1z64p4K3y8yqqq04OQOm

22632 Federal Register / Vol. 51, No. 119 / Friday, June 20, 1986 / Rules and Regulations excess disease risk has been observed are the product of well designed and comments and testimony submitted at cumulative exposures at or below conducted studies of relevant human regarding the quantitative assessment of those permitted by the existing OSHA 8hour permissible exposure limit of 2 f/ cc. In addition, OSHA has made risk 1 estimates of the excess mortality from lung cancer, mesothelioma, populations. . . . When an occupational hazard has been identified, useful epidemiologic study results will determine the quantitative relationship between the dose of exposure to the causative agent and the risk of the adverse health response in the risk for asbestos. OSHA's proposed estimates of risk may be found in Ex. 84-392, the emergency temporary standard ("the November proposal", 48 FR 51086|. and in the April proposal [49 gastrointestinal cancer, and the exposed population. The product is Ihc FR 14116|. incidence of asbestosis using mathematical models that describe the data observed in epidemiologic studies conducted in various industrial populations. In many cases, the elevated risks seen in.worker populations reflect past exposures that were higher than those permitted today. OSHA's quantitative risk assessment entails using the directly observed risks from these past exposures to estimate risk at lower exposure levels. OSHA believes this is a scientifically appropriate and valid procedure. In some instances, OSHA estimated risks using studies which actually observed risks at or below cumulative exposures permitted by the existing standard. The range of studies used by OSHA covers many different work situations and exposure levels. Where possible, OSHA has quantified the ranges of uncertainties in the estimates. These numerical estimates, as well as those risks observed at low exposure-response relationship, which together with a valid eslimnte of the size of Ihc exposed population, the extent of that exposure and accurate indicators of the disease outcome, give characterization of the risk [Ex. 99, p. 8). The potency coefficients for lung cancer and mesothelioma (Ki. and KM, respectively) used to define the doseresponse relationship were calculated for each study so that cancer mortality was estimated for various exposure levels and exposure durations. A number of well-conducted and high quality epidemiologic studies were available that contained sufficient information on which to base a quantitative risk assessment. Some of these studies did not contain exposure data, but could be coupled with exposure information from other sources in order to obtain an estimate of KE and K,,. OSHA chose not to use animal studies to predict quantitative estimates of risk from asbestos exposure because of the I. Estimates of Risk for Lung Cancer A. The Model. As discussed in the November proposal, OSHA chose a linear model to describe the relationship between the excess relative risk of lung cancer and asbestos exposure (dose). Relative risk is defined as the ratio of the mortality rate of exposed persons to the mortality rate of equivalent nonexposed persons. Relative risk is frequently approximated by the standardized mortality ratio (SMR). which is the observed number of deaths in the exposed population divided by the number of deaths that would be expected in the exposed population. The number of expected deaths is usually derived from the specific age, sex. and calendar year mortality rates in the comparison population. Asbestos exposure is generally measured in terms of total or cumulative dose. Total dose, also referred to as cumulative exposure or cumulative exposures, were evaluated to determine many high quality human studies dose, is a measure of the amount of the significance of the risk and to determine whether the new standards will lead to a substantial reduction in available that were conducted in actual workplace situations. As is often the case with animal studies, laboratory asbestos inhaled; it is the product of the duration of exposure (in years |y|) and the intensity of exposure (which is risk. conditions may not precisely parallel workplace air concentration in millions OSHA's critical evaluation of all actual worksite exposures. In the case of of particles per cubic foot [mppcf] or relevant animal and epidemiological asbestos, for example, is it not clear in fibers per cubic centimeter [f/cc|). studies resulted in the selection of eight all instances whether laboratory Under this definition of exposure, a studies that contain good data for the animals have been exposed to fiber size person exposed to airborne asbestos at calculation of the dose-response distributions similar to those found in 2 f/cc for 20 years (40 fiber-years/cc [f- relationship for lung cancer for this final workplaces. In addition, asbestos y/cc]) has the same total dose as a rule [Selikoff et al,, 1979. Ex. 84-90: appears to multiply the underlying lung person who is exposed to asbestos at 4 Seidman. 1984. Ex. 261-A; Henderson cencer risk of smoking and nonsmoking f/cc for 10 years (40 f-y/cc). and Enterline. 1979, Ex. 84-48; Weill et workers: laboratory animals generally The relative risk model used by at.. 1979, Ex. 84-206; Finkelstein, 1983. do not have any underlying risk of lung OSHA in assessing the risk of Ex. 84-240: Peto. 1980, Ex. 84-169; cancer. Instead of relying on the animal developing lung cancer from asbestos, Dement et al., 1982, Ex. 84-35; Berry and studies to estimate risk, OSHA has exposure is described by the following Newhouse. 1983, Ex. 84-21) and six for supplemented the human data with equation: mesothelioma [Selikoff et al.. 1979, Ex. results from animal studies when 84-90; Seidman et al., 19B4, Ex 261-A; evaluating the health information and RL=Rt(i-KM fxd,-,<,)) (Eq. i) Finkelstein. 1983. Ex. 84-240; Peto. 1980, determining the significance of the risk; Ex. 84-169; Weill et al., 1979, Ex. 84-206; OSHA believes that the animal studies where RL is the lung cancer mortality and Dement et al,, 1982, Ex. 84-35]. In can provide valuable qualitative resulting from the asbestos exposure, RE general, studies of human cohorts in the information on asbestos-related disease. is the expected mortality in the absence workplace should provide a better basis For example, the animal studies show of exposure, f is the intensity of for quantitative risk assessment than that all commercial asbestos types can exposure in fibers/cc. d is the duration studies of experimental animals because cause cancer and pulmonary fibrosis. of exposure in years, t is the time from of the similarities in the populations at Animal studies also indicate that longer, the onset of asbestos exposure in years risk and the populations from which the thinner fibers may have greater (minus 10 years to allow for a minimum risk'1 estimates are derived. As Dr. Hans carcinogenic potency than short, coarse latent period) and Ku is the Weill, testifying on behalf of OSHA, fibers. proportionality constant that is a noted: The paragraphs below provide a measure of the carcinogenic potency of : .The greatest public confidence in decision synopsis of OSHA's quantitative risk making to reduce an environmental or estimates derived from mathematical the asbestos exposure (slope of the dose-response curve). occupational risk results when the data used models and a discussion of the The equation can be rewritten as GLEASON-000880