Occupational exposure limit concentration, calculation

The TL and MAK values should be used as guides in the control of health hazards. They are not constants that can be used to draw fine fines between safe and dangerous concentrations. Nor is it possible to calculate the TL or MAK values of solvent mixtures from the data in Table A-13, because antagonistic action or potentiation may occur with some combinations. It should be noted that occupational exposure limits such as the TL and MAK values are not intended for use as a comparative measure of one solvent against another. The values set airborne concentration limits on chemical exposure, but do not describe the ease with which that airborne limit is achieved. In addition, the vapour pressure of the solvent must also be considered. The lower the vapour pressure, the lower the airborne concentration. In order to better compare the safety of volatile compounds such as organic solvents, the use of the vapour hazard ratio ( VHR) has been recommended as a feasible measure [175], The vapour hazard ratio is defined as the quotient of the saturation concentration of a solvent (in mg/m at a given temperature and pressure) and its occupational exposure limit (in mg/m e.g. TL or MAK values), according to ... 

Lung Cancer and Mesothelioma Based on an analysis of data from epidemiologic studies of workers who were exposed to asbestos before modem occupational exposure limits were established, EPA (1986) calculated by extrapolation that lifetime exposure to asbestos air concentrations of 0.0001 fiber/mL could result in up to 2 to 4 excess cancer deaths (lung cancer or mesothelioma) per 100,000 people. This air concentration is within reported ranges of ambient air levels (0.00001 to 0.0001 liber/mL). The EPA analysis has been extensively discussed and reviewed in the scientifrc literature (Camus et al. 1998 ... 

Phosgene cannot be detected by smell (see Section 3.1.3) at the generally accepted occupational exposure limit of 0.1 p.p.m. [43,1703]. Although the sense of smell undoubtedly acts as a natural safety detection warning system, the accepted odour threshold is approximately ten times the TLV-TWA. The odour safety factor (TLV/odour threshold) has been calculated as 0.11, and the material has been assigned an odour safety elassification "E" to suggest that less than 10% of attentive persons can detect the gas at a concentration corresponding to its TLV [43]. 

The degree of protection required will be the factor by which it is necessary to reduce the airborne concentration of the contaminant in order to limit the exposure to below the occupational exposure limit. A fraction of the OEL, i.e. one-tenth, is usually chosen as a suitable level of protection. The degree of protection provided by a specified piece of RPE is given by a designated nominal protection factor (NPF), which is defined as the ratio of the concentration of contaminant present in the ambient atmosphere to the calculated concentration in the breathing zone when the RPE is being worn. 

Calculation of the occupational exposure concentration (OEC) depends on the type of OEL. For example, when the limit value has been set as an eight-hour time-weighted average, the cumulative exposure for an eight-hour work shift should be computed as follows ... 

In the European community, the occupational exposure level is defined as the limit of the time-weighted average of a chemical agent in the air within the breathing zone of a worker in relation to a specified reference period, usually 8 h or a work shift. In addition, to avoid adverse health effects, there is a need to set limits for short-term exposure peaks. In the occupational safety legislation of most countries within the European Community the lists of occupational exposure levels include limits for short-term exposure for many substances, either in the form of definite concentration values or so-called short-term exposure factors. In case of factors, the allowed maximum short-term concentration is calculated by multipHca-tion of the OEL by the short-term exposure factor. Typically, many hazardous substances have factors within the range of 1-4. 

Selection of the Key Study. The most reliable data to use in calculating RfDs are subchronic or chronic human studies using the appropriate exposure route however, such data for CK are limited to one subchronic occupational exposure study (Reed 1920) that did not provide exposure concentrations. There were no subchronic or chronic animal data from which to develop an RfDe for CK. Acute human exposure data could be used to establish short-term exposure limits however, there is insufficient information to indicate whether chronic adverse effects would be avoided if exposures were maintained below levels at which acute toxicity would occur. 

Two of the standards directly related to worker health and important in design work are Toxic Hazardous Substances and Occupational Noise Exposure. The first of these two concerns the normal release of toxic and carcinogenic substances, carried via vapors, fumes, dust fibers, or other media. Compliance with the Act requires the designer to make calculations of concentrations and exposure time of plant personnel to toxic substances during normal operation of a process or plant. These releases could emanate from various types of seals and from control-valve packings or other similar sources. Normally, the designer can meet the limits set for exposure to toxic substances by specifying special valves, seals, vapor-recovery systems, and appropriate ventilation systems. 

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