H2S is a gas with a strong odor you can’t always smell
Rotten Egg Odor
Hydrogen sulfide is formed from the decay of decomposing organic matter such as in oil and gas reservoirs. It is known for having a distinctively sulfurous odor similar to that of rotten eggs. One area near San Antonio where one can smell H2S is in the oilfields just east of the city near Luling, Texas. When hydrogen sulfide is burned it creates a gas called Sulfur Dioxide, which has its own sulfurous and obnoxious odor. Depending on the temperature and oxygen content of the gas stream during combustion, the burning of H2S into SO2 may not be complete and flares can often give off the sulfurous odors of both H2S and SO2.
Fatiguing the olfactory nerve
Hydrogen sulfide is a potent gas when it comes to slowing down activity in the nervous system. The ACGIH has listed the lowest intermediate term minimum risk level at which hydrogen sulfide starts to create an effect on the nervous system as 0.03 PPM. Once the level of H2S reaches about +-50 parts per million the ability of the olfactory nerve, which detects smell, starts to become fatigued from the increasing toxicity of the hydrogen sulfide gas. While at lower levels the H2S may have had a powerful odor, as the H2S concentration increases to and above this higher level the ability to smell will wane and the actual odor will decrease. For anyone using their sense of smell to try to detect hydrogen sulfide this is unfortunately deceptive because as the hydrogen sulfide gas nears dangerous levels it will become continuously more undetectable as hydrogen sulfide attacks the olfactory nerve. All workers must be trained to the proper way of responding to this hazard.
Detecting H2S the right way
The correct way to protect people from exposure to unhealthy and unsafe exposure to hydrogen sulfide gas is through the proper use of personal and stationary H2S gas monitors. Personal gas monitors need to be placed into the breathing zone while stationary monitors will have other strategic importance based on living and working spaces versus possible hydrogen sulfide sources. Before entering any confined space, it must also be cleared by drawing a sample and having the atmosphere tested for any dangerous gasses including hydrogen sulfide. Certified H2S gas monitors are not subject to fatigue the same way that the human olfactory nerve is.
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