Typical exposure levels have been established ( note - these may differ based upon geographical location): Permissible Exposure Level (PEL) 5 ppm Short Term Exposure Level (STEL) for 15 minutes 10 ppm Only self-contained breathing apparatus respirators are approved for protection against hydrogen sulfide. Exposure Exposure to low concentrations cause irritation of the skin, eyes and air passages. H 2 S is absorbed by the blood, combines with the hemoglobin and produces asphyxia. High concentrations cause sudden paralysis of the respiratory system resulting in coma and rapid death. Treatment speed is critical. Victims must be removed to fresh air immediately. If breathing has stopped, give artificial respiration at once as they will NOT resume breathing on their own. Call for immediate medical assistance. H2S is heavier than air. This factor adds to the potential danger of the toxic and explosive effects of H2S. Be especially cautious of low-lying areas and natural wind breaks.
1.4.2 Hydrogen Sulfide Hydrogen Sulfide (H 2 S) is probably the most dangerous gas commonly encountered in the petroleum industry. Although rarely handled as a commercial commodity, it is found in almost all crude oils and even refined products, especially fuel oils. Both petroleum refineries and natural gas processing plants must treat H 2 S, which is an unwanted pollutant, and a potential source of exposure. The term "sour" is usually applied to crude oils and gas feedstocks that have high concentrations of H 2 S. The sense of smell is not reliable for detecting the level of concentration of hydrogen sulfide. At 100 ppm the sense of smell is deadened within minutes. H 2 S is a colorless gas which has a sweetish taste and an unpleasant odor of "rotten eggs". There are three major hazards associated with hydrogen sulfide; toxicity, flammability and corrosion. However, the most consistently dangerous of these three hazards is toxicity. H 2 S is very poisonous, being 5 times as toxic as carbon monoxide and almost as toxic as hydrogen cyanide. While H 2 S can be detected nasally at concentrations as low as 0.2 ppm, even relatively low concentrations rapidly paralyze the olfactory nerves and lead one to a false sense of security.
Gauging and Sampling Always check in with the terminal / refinery shift supervisor prior to entering active work areas. Facilities that handle benzene are required to determine and designate areas where high concentrations of benzene vapor are likely. Be on the lookout for posted "Benzene Designated Areas". Never enter such an area without respiratory protective equipment. Whenever possible, you should not work over openings in tanks that are actively receiving benzene. If this should happen, you MUST wear a self-contained breathing apparatus unit. A full- face piece respirator with organic vapor cartridges is mandatory when performing manual gauging and / or sampling of benzene or, if there is a splash or spill hazard. Viton or nitrile gloves must be worn when contact with skin is possible. Neoprene boots and chemical suit must also be worn if a splash or spill is possible. A safety data sheet (SDS) is an excellent source of safety information and is also an essential part of our "hazard communication program" (hazcom). Personal hygiene is very important when handling benzene or any other chemical. Always keep food and drink away from chemicals and their vapors; and wash your hands thoroughly before eating or drinking.
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