H2S - A Toxic Gas That Can Kill
Authors: Atherton Stanley 
Published: December 2007

An old soap advertisement I recall stated that the product was "99.44 percent pure - it floats!" While product was "99.44 percent pure - it floats!" While this may be an excellent standard for soap, it is a lethal atmosphere if that which remains is hydrogen sulfide gas.

To give you a better idea of the small "percent by volume" dilution required to create a fatal atmosphere, let us assume that we are in a room that is 10 × 12 × 10 ft. Such a room would contain 1,200 cu ft. If it contained only 1 cu ft (833 ppm) of hydrogen sulfide gas and 1,199 cu ft of pure atmosphere, it would be lethal. In one breath, you would become unconscious immediately.

As some of you may recall during the earlier days of refinery distillation all of the streams from the stills flowed into the receiving houses to be observed and sampled, then on to selected tankage. Since these streams flowed through the lines into glass boxes with unsealed caps or lids and the vacuum line was sometimes over-capacitated, it was always possible during certain periods for large amounts of hydrocarbon gases containing H2S to escape, exposing personnel. It was not unusual then to see operators wearing approved respiratory protective equipment for extended periods, especially the approved canister-type H2S mask. Likewise, today personnel wear the appropriate breathing apparatus for the H2S concentration involved during sampling, gauging, and other work activities in which sour crudes are handled.

However, despite the information available on H2S, and despite the fact that personnel know and understand the hazards involved with H2S, including the necessary precautions to be taken, serious injuries and fatalities still occur as a result of exposure to the toxic gas. Sour crudes, both domestic and foreign, must be handled with respect. We cannot become complacent. If we do, our respect for the danger of H2S diminishes and sooner or later we are trapped.

As we know, high amounts of H2S are produced at the wellheads. The flow moves on from the well to the tank, to the gas plants and compressor stations and into the refineries. Practically all phases of the industry must cope with H2S gas at different stages and make provisions to reduce exposure to employees as well as to prevent accelerated corrosion of the equipment used in the handling of it.

Because we are still faced with problems from H2S. we continue to highlight its properties, its toxicity, and the personal protective equipment required, and we maintain a program of continuous employee education and training.

As we know it, hydrogen sulfide (H2S) is a colorless gas with a definite odor that is generally referred to as the smell of rotten eggs. However, to those who may not have smelled rotten eggs, I would say that it is an acidic gas. The odor itself is not reliable as an indicator to warn that it is in dangerous concentration because the higher concentrations have a paralyzing effect on the olfactory nerve. H2S, even in paralyzing effect on the olfactory nerve. H2S, even in low concentrations, irritates the eyes and respiratory tract. Also, increased concentrations of H2S become progressively more harmful. Inhalation of high progressively more harmful. Inhalation of high concentrations of H2S causes death immediately.

H2S is dangerously reactive with strong acids and oxidizing materials. If the solutions that have absorbed hydrogen sulfide are heated, the gas may be liberated in hazardous volumes. Industrial uses of hydrogen sulfide are limited.

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