CompuServe Messages

Jim- Thanks for the summary of H2S toxicology. It is what I have intended to post for some time, but haven't somehow coordinated (wonder if a busy schedule is any factor). I work in a sulfuric acid plant that processes up to 84 tons of H2S per day. In 37 years, we have had zero incidents involving plant personnel. Although 28 years ago, we did experience a significant leak in a pipeline that did kill a rabbit and three birds. Most forum members will not be exposed to substantial risk in their normal activities, however there are some circumstances in the field where significant concentrations of H2S can occur: Sulfide zones of ore deposits evolve H2S which is slighty heavier than air. Localized areas of fatal concentrations can occur. Coal deposits and some carbonaceous shales are another potential exposure. Hydrothermal zones near active volcanoes or other geothermal structures. If sulfur deposits are present, you can bet H2S was the source. SO2 (sulfur dioxide) is less lethal than H2S at similar concentrations, yet its PEL (permitted exposure limit) is 5 ppm or half the allowable exposure limit of H2S. SO2 has such an irritating effect on mucosal membranes that rarely will an individual chose to remain in exposure for long, and certainly it warns you well before you hit a lethal level. The toxicity of H2S is due to its chemical binding with haemoglobin forming methaemoglobin. The oxygen carrying capacity of the circulatory system is rapidly and significantly diminished. Fortunately, the effects are relatively quick to reverse, provided the victim is removed to an H2S free area. There is a marvelous training film on H2S that demonstrates the effect of H2S exposure and subsequent recovery on a rat. Regards- Michael