Asbestos exposure levels

Cover the general requirements for monitoring to determine asbestos exposure levels. Each employer who has a work operation where exposure monitoring is reqiiired must perform monitoring to determine the airborne concentrations of asbestos to which employees could be exposed. Determinations of employee exposure have to be made from breathing zone air samples that are representative of the 8-hour TWA and 30-minute short-term exposures of each employee. 

Asbestos exposure levels.Occupational Health — Citations — Asbestos... 

The replacement of asbestos fibers by other fibrous materials has raised similar health issues in relation to substitute materials. However, since lung cancer has a latency period of approximately 25 years, and since the fiber exposure levels in contemporary industries is far lower than those which prevailed half a century ago, the epidemiological data on most substitutes is insufficient. A possible exception is slag fibers for which several studies on worker populations are available over extended periods (44) some results show a substantial increase in lung cancer occurrence. Consequentiy, the toxicity of asbestos substitute fibers remains a subject of active investigation. 

Requirements for the control of asbestos exposures at work. Exposure is to be prevented or, if this is not reasonably practicable, reduced to the lowest level reasonably practicable by measures other than the use of respiratory protective equipment. 

The confusion and frustration of nonepidemiologists, especially those who must act on hehalf of the public, contribute further to the disarray. For ethical reasons, they propose regulations that seek the lowest possible level of asbestos exposure. But economics, not to mention common sense, continues to bring the results of these decisions to our attention. Inorganic fibers are ubiquitous. Are asbestos and other fibrous materials major health hazards for the world s population ... 

In Beshada v. Johns-Manville Products Corp., 90 N.J. Supreme Court (1982), the court held the defendant liable even though the hazards associated with low-level asbestos exposure were unknown and unknowable. 

The main route of exposure, however, is by inhalation of the fibres. Asbestos causes three types of adverse effects asbestosis, bronchial carcinoma, and mahgnant mesothelioma. The latter two are types of cancer, with mesothelioma associated only with exposure to asbestos. The mechanisms by which asbestos causes cancer are not fuUy understood, although some features are known (see box), such as the size of fibre (only fibres of certain sizes are hkely to cause disease). All forms of asbestos can cause asbestosis and bronchial carcinoma if the exposure level and length of exposure are high enough. 

Bronchial carcinoma also develops in those who have prolonged heavy exposure to asbestos and occurs in approximately 50 per cent of those who have asbestosis. The risk of contracting these diseases, and their severity are related to the exposure level, with the length of exposure being another factor. 

Levels of exposure associated with carcinogenic effects (Cancer Effect Levels, CELs) of asbestos are indicated in Tables 3-1, 3-2, and 3-3 and Figures 3-1, 3-2 and 3-3. Because cancer effects could occur at lower exposure levels. Figures 3-1 and 3-4 show a range for the upper bound of estimated excess risks, ranging from a risk of 1 in 10,000 to 1 in 10,000,000 (lO " to 10 ), as developed by EPA. 

Overview of Health Effects. Studies in humans and animals indicate that inhalation of asbestos fibers may lead to fibrotic lung disease (asbestosis), pleural plaques and thickening, and cancer of the lung, the pleura, and the peritoneum. It may also increase the risk of cancer at other sites, but the evidence is not strong. Significant effects on other tissues have not been detected. A number of researchers have found that the occurrence of asbestosis and lung cancer correlates with cumulative exposure (that is, the product of concentration [PCM fibers/mL] multiplied by years of exposure). Therefore, human exposures are expressed below as PCM f-yr/mL. Animal data are provided in terms of exposure level (PCM f/mL) and duration, and the cumulative exposure can be found simply by calculating the product. However, due to differences in clearance rates and lifespan as well as other differences, cumulative doses in animals are not expected to be directly comparable to cumulative doses in humans. Studies that provide reliable dose-... 

Using a predictive model developed from mesothelioma data from studies of asbestos insulation workers (Peto et al. 1982), asbestos textile workers (Peto 1980), amosite factory workers (Seidman 1984), and asbestos-cement workers (Finkelstein 1983), EPA (1986a) estimated that continuous lifetime exposure to air containing 0.0001 f/mL of asbestos would result in about 2-3 cases of mesothelioma per 100,000 persons. The corresponding cumulative lifetime exposures associated with excess risks of 10 " -10 are shown in Figure 3-1. Cumulative exposure levels of 0.031, 0.0031, 0.00031, and 0.000031 f-yr/mL represent excess mesothelioma risks of 10" , 10 , 10, and 10 ", respectively. Appendix D provides further details on the derivation of these risk estimates. Currently (in 2001), EPA is in the process of reviewing their cancer risk estimates for asbestos fibers. 

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