As recommendations for industry, they do not have the force or effect of law. These are recommendations for breathing zone concentrations, which should not be exceeded in the workplace. The American Conference of Governmental Industrial Hygienists (ACGIH) has adopted a Threshold Limit Value (TLV) of 0.5 ppm (8 hour time-weighted average) and a Short Term Exposure Limit (STEL) of 2.5 ppm (15 minute time-weighted average). 71 The ATSDR has derived an Intermediate Inhalation MRL of 0.004 ppm for benzene based on a LOAEL for neurological effects in mice. The Agency for Toxic Substances Disease Registry (ATSDR) has derived an Acute Inhalation Minimal Risk Level (MRL) of 0.05 ppm for benzene based on a Lowest Observed Adverse Effect Level (LOAEL) for immunological effects in mice. The National Institute for Occupational Safety and Health (NIOSH) has adopted a Recommended Exposure Limit for benzene of 0.1 ppm (8 hour time-weighted average) and a Short Term Exposure Limit of 1 ppm (15 minutes). These limits have the effect of law and represent maximum allowable exposures in the workplace. Occupational Safety and Health Administration (OSHA) defines the Permissible Exposure Limit to be 1 ppm (8 hour time weighted average) and Short Term Exposure Limit to be 5 ppm (15 minute average). The regulations and recommendations for limiting benzene exposure are summarized below. Several organizations and governmental agencies prepare regulations or recommendations limiting exposure to toxic chemicals. Kilburn, in Handbook of Solvents (Third Edition), 2019 19.4.6.2 Benzene exposure limits and recommendations These are classified as confined spaces, and access to them has to be tightly controlled. There may be some substantially enclosed areas which may have flammable, toxic or asphyxiating atmospheres which we cannot design out. Note that there are many substances which are both toxic and flammable, and both hazards should be considered simultaneously. Failing that, we can use engineering controls such as ventilation, avoidance of enclosure, controlling access to contaminated areas, and so on. If we identify excessive exposure to toxic chemicals in our design, we should first consider substituting the materials which produce toxic hazards. The HSE Publication EH40 gives exposure limits for a wide range of chemicals (see “Further Reading”). The short-term exposure limit (STEL) is the time-weighted average concentration of a substance over a 15 min period thought not to be injurious to health. The long-term exposure limit (LTEL) is the time-weighted average concentration of a substance over an 8-h period thought not to be injurious to health. Seán Moran, in An Applied Guide to Process and Plant Design, 2015 Toxic hazards
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