Limiting Long-Term Exposure

The physician K.B. Lehmann observed in the course of his factory inspections and as a result of animal and other experiments in the years 1884 to 1886 that there exists an airborne concentration for any substance below which no occupational disease develops. This is true independently of the time of exposure. This realization led to the development of the MAK values (MAK maximum occupational 

These values nowadays are only of historical interest. Instead the Technical Rules for Hazardous Materials are used [47]. They contain threshold values for occupational exposure. Table 2.34 gives the corresponding values for selected materials, which are frequently used in the process industry. The values apply to a working life with a five-day week and 8 h of daily work. They are called workplace threshold values (AGW). Additionally, there is a transgression factor catering for short-time exposure to higher concentrations (vid. [47]). 

For practical applications it is often necessary to convert ppm into mg m and vice versa. This is done by 

Fixing thresholds below which no impact is to be expected encounters limitations in the case of carcinogenic substances. This is why recently a probability-related concept was proposed for such substances (vid. [49] and Sect. 8.2). 

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P) Occupational Exposure Limits long-term exposure (8-h TWA period),... 

Butylenes are not toxic. The effect of long-term exposure is not known, hence, they should be handled with care. Reference 96 Hsts air and water pollution factors and biological effects. They are volatile and asphyxiants. Care should be taken to avoid spills because they are extremely flammable. Physical handling requires adequate ventilation to prevent high concentrations of butylenes in the air. Explosive limits in air are 1.6 to 9.7% of butylenes. Their flash points range from —80 to —73° C. Their autoignition is around 324 to 465°C (Table 2). Water and carbon dioxide extinguishers can be used in case of fire. 

Many very hazardous solvents, such as benzene and carbon tetrachloride, were widely used until the 1970s. The situation was very similar for the use of pesticides. Among the toxic pesticides that were still in wide use 20 years ago were chlorophenols, DDT, lindane, and arsenic salts, all of which are classified as human carcinogens as well as being acutely toxic. Fortunately, use of these kinds of very toxic chemicals is now limited in the industrialized world. However, because the number of chemicals used in various industries continues to increase, the risks of long-term health hazards due to long-term exposure to low concentrations of chemicals continues to be a problem in the workplace. 

Long-term exposure limit (LTEL) An exposure limit requirement based on the assumption that the total body intake of a pollutant below this limit over an 8-hour working day will have no harmful effect on the worker over a working life. See also Maximum exposure limit (MEL), Occupational exposure limit (OEL), and Short-term exposure limit (STEL). 

It is an accepted practice when assessing the environmental effects of pollution on man and his place of abode to use a divisor of 40 (some agencies may divide by 30) against the long-term exposure level in the Occupational Health and Safety Act (OSHA). Much lower exposure limits are necessary due to the much longer term of exposure in the domestic situation. The section of the population most likely to spend long periods of time in the home are those most susceptible to the detrimental effects of pollutants, i.e. the young, the elderly or the infirm. For short-term exposure the known data can be used directly from the list or from animal-exposure data. 

This may be due, in part, to the limited information on toxic effects associated with such exposures. If additional information becomes available indicating adverse health effects of long-term exposures, then studies examining methods for mitigating the effects of such exposures would become a data need. 

There have been a nnmber of estimates of bioconcentration factors for total PCBs in aqnatic species following long-term exposure to PCB mixtures (EHC 140). Values for both invertebrates and hsh have been extremely variable, ranging from values below 1 to many thonsands. Bioaccnmnlation factors for birds and mammals for different Aroclors have indicated only limited degrees of bioaccumulation from food, for example, 6.6 and 14.8 for the whole carcasses of big brown bats Eptesicus fuscus) and white pelican (Pelecanus erythrorhynchos), respectively (see Environmental Health Criteria 140). 

Specific short-term exposure limits are listed by the HSE for those chemicals which pose a risk of acute effects from brief exposures. For other chemicals a recommended guideline for controlling short-term excursions is to restrict them to 3x long-term exposure limit averaged over a 10min period. 

Magnetic equipment, 15 434—435 Magnetic field exposure limits, long-term, 16 527... 

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