Thursday, April 23, 2009

Hydrogen Sulfide Gas

If you wait for a warning, it may be too late

Hydrogen sulfide is a powerful and deadly gas which smells like rotten eggs at low concentrations and has a sweet smell at high concentrations. But workers should not rely on the smell as a warning. At high concentrations H2S may overcome one's sense of smell. The result could be instant death. Long exposure to low concentrations will also deaden the sense of smell.

What it is

H2S is explosive - it will ignite and explode when subjected to a spark or ordinary flame - in any concentration from 4% to 44% of the air. It is also soluble in water and oil, so it may flow for a considerable distance from its origin before escaping above ground or in an entirely unexpected place. Because the vapor (gas) is heavier than air, it may travel for a long way until ignited and then flash back towards the source.

Where is it found?

Hydrogen sulfide is found in large amounts in natural gas and petroleum. Any worker involved in extracting gas and petroleum from the ground, or in storing, transporting or processing gas is at risk from exposure to H2S Hydrogen sulfide exists in solution in crude oil, and workers are exposed when the gas begins to "pass off" as it reaches the surface or comes into contact with air. This can occur at any point, including all stages of the refining operation, and it is accelerated by heat or hot weather.

H2S Sources

H2S is found widely in industry and few workers are warned of its dangers or their exposure. It is formed by the decomposition of organic materials, so it is found in natural gas and oil, in mines, wells, fertilizers, sewers, and cesspools. It is given off as a by-product in the manufacture of rayon, synthetic rubber, dyes and the tanning of leather.

Health Effects of H2S acute exposure

First of all, and most important, H2S can kill you. The extent of acute poisoning danger depends on the concentration of H2S in the atmosphere.
When you breathe in H2S, it goes directly through your lungs and into your bloodstream. To protect itself, your body "oxidizes" (breaks down) the H2S as rapidly as possible into a harmless compound. If you breathe in so much H2S that your body can't oxidize all of it, the H2S builds up in the blood and you become poisoned. The nervous centers in your brain which control breathing are paralyzed. Your lungs stop working and you are asphyxiated - just as though someone had come up and put their hands around your neck and strangled you. A worker can be overcome by H2S and lose consciousness in a few seconds; luckily if he is rescued in time and is given artificial respiration within a few minutes, the worker may recover. Either artificial mouth-to-mouth or an oxygen supply system of resuscitation will work if it is done in time, because, with an adequate source of oxygen and no further H2S intake, the body will quickly break down the H2S still in the blood.

This is acute poisoning. It can occur with no warning at all, since even the sense of smell may be overcome, and it can be fatal within a few seconds.

Although acute poisoning is deadly if it is not caught in time, when caught and treated it is reversible and this is why rescue attempts with proper safety equipment are so important.
Recent evidence has shown irreversible brain damage from acute high doses.

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