Exposure, occupational definition

The human experience regarding exposure to dimethylhydrazines is limited to case reports describing severe but nonlethal effects following accidental acute exposures. There are limited data suggesting subclinical hepatotoxicity following subchronic occupational exposure to unspecified low levels of 1,1-dimethylhydrazine. No definite exposure concentrations or durations were available in these reports, and the data are not useful for quantitative derivation of AEGLs. 

Fiber has been given a legal, if not operational definition, at least as it applies to asbestos. Unfortunately tlie definition bears little relationship to the present use of the term. It was essential to set standards to reduce occupational exposure but the detection, identification, and suppression of asbestos materials opened several areas of problems that remain unsolved. For example, six minerals are included in the definition of asbestos. Are they all equally hazardous If not, why not There are many other inorganic particles with diameters of less than 3 micrometers and a diameter-to-length ratio of 1 3. Should we be concerned that they too might be hazardous to our health ... 

These two definitions reflect two sides of the same situation. In this book, the term critical effect(s) will be used for the hazard/effect considered as being the essential one(s) for the purpose of the risk characterization, e.g., for the establishment of a health-based guidance value, permissible exposure level, or Reference Dose. It should be noted that the critical effect could be a local as well as a systemic effect. It should also be recognized that the critical effect for the establishment of a tolerable exposure level is not necessarily the most severe effect of the chemical substance. For example, although a substance may cause a serious effect such as liver necrosis, the critical effect for the establishment of, e.g., an occupational exposure limit could be a less serious effect such as respiratory tract irritation, because the irritation occurs at a lower exposure level. 

Many dietary and environmental factors have been implicated as possible etiologic factors in the development of pancreatic cancer, but no definite causal relationships have been established. The strongest evidence points to cigarette smoking as a risk factor associated with pancreatic cancer (20-24). Occupational exposure to certain chemicals has also been linked to pancreatic carcinoma (25). Others in the high-risk group include stone miners, cement workers, gardeners, textile workers, and leather tanners (17,26). 

The most commonly accepted definition of MCS was written by Mark Cullen, M.D., a professor of medicine and epidemiology at Yale University. In Workers With Multiple Chemical Sensitivities, Occupational Medicine 2 (1987) 655-626, he writes, Multiple chemical sensitivities is an acquired disorder characterized by recurrent symptoms, referable to multiple organ systems, occurring in response to demonstrable exposure to many chemically unrelated compounds at doses far below those established in the general population to cause harmful elfects. No single widely accepted test of physiologic function can be shown to correlate with symptoms. ... 

There is no clear definition for the terms safe exposure limit (SEE) and occupational exposure limit (OEL), although the terms has scientific and legal interpretations and implications. The values of SEE or OEE vary from country to country around the world. It is well known that a rough rule of thumb is that the SEEs and OEEs are levels below which most industrial workers and the general population could get exposed to chemical substances on a regular basis with a low risk to health. It should be clearly understood that SEE and OEE are certainly not levels that are definitely safe and below which no harm is caused. 

Potential occupational carcinogen means any substance, or combination or mixture of substances, which causes an increased incidence of benign and/or malignant neoplasms, or a substantial decrease in the latency period between exposure and onset of neoplasms in humans or in one or more experimental mammalian species as the result of any oral, respiratory, or dermal exposure, or any other exposure which results in the induction of tumors at a site other than the site of administration. This definition also includes any substance... 

Cohort Definition and Follow-Up Period A variety of sources of information are used to identify workers exposed to a particular workplace hazard, to construct an occupational history, and to complete the collection of information necessary for tracing (see below). It is essential that the cohort be well defined and that criteria for eligibility are strictly followed. This requires that a clear statement be made about membership of the cohort so that it is easy to decide whether an employee is a member or not. It is also important that the follow-up period be carefully defined. For instance, it is readily apparent that the follow-up period should not start before exposure has occurred. Furthermore, it is uncommon for the health effect of interest to manifest itself immediately after exposure, and allowance for an appropriate biological induction (or latency) period may need to be made when interpreting the data. 

The immediately dangerous to life or health (IDLH) air concentration values have been recommended by the US National Institute for Occupational Safety and Health (NIOSH) as respirator selection criteria. The current NIOSH definition for an IDLH condition is a situation that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment. NIOSH s stated purpose for establishing IDLH values is to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment. The complete introduction and documentations to the 398 existing IDLH values can be read or downloaded at the NIOSH Internet website. 

One problem with these definitions is that the relationship between the symptoms and the exposure is solely dependent on the patient s report. Further, patients with MCS are generally polysymptomatic and report sensitivities to multiple unrelated substances. In addition, cross-sectional studies indicate that persons diagnosed with MCS have impaired social and occupational adjustment and exhibit other characteristics... 

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