HYDROGEN SULFIDE is a DEADLY GAS

Hydrogen Sulfide warning sign, courstesy OSHA.gov.

Hydrogen sulfide gas [H2S(g)] is referred to as sewer gas, swamp gas, and other equally endearing terms, because it's the deadly gas that is generated in the anaerobic conditions of stagnant, confined sewage (among other places). Concentrations can be up to 6,000 ppm. Hydrogen sulfide can be detected with an odor like rotten eggs, at a level of 0.5 parts per billion (ppb).1 For a frame of reference, 1 mL of the gas distributed evenly in a 100-seat lecture hall is about 20 ppb.2 Now can you picture 0.5 ppb? Me neither. But what matters is that we're talking about exceedingly minute amounts here.

Low-level inhalation exposure causes nausea, dizziness, and headache. Symptoms from repeated, low-level exposure usually disappear a while after the exposure is ended.3 Prolonged exposure to low concentrations can cause painful dermatitis and burning eyes.4 Higher concentrations of the gas, which don't smell any more intense than small concentrations, cause collapse, coma, and death from respiratory failure. And in fact, at 300 ppm the odor no longer registers with the olfactory nerve, and is considered IDLH (immediately dangerous to life and health) at 100 ppm. At 600 ppm the lungs begin to fill with the gas (instead of oxygen) and breathing is compromised. At levels higher than this, paralysis of the lungs occurs within 2-3 breaths.5 OSHA has set the permissible exposure limit to 10 ppm for an 8-hour day.

WHERE DOES H2S(g) OCCUR?
It occurs naturally in volcanic gases & hot springs, crude petroleum, natural gas, and when organic matter decomposes. Industrially it occurs in some food processing plants, petroleum refineries, coke ovens, paper mills, tanneries, sugar beet processing, and hot-asphalt paving. Residentially it can occur from faulty plumbing or malfunctioning sewer drains, which allows the gas into the house.6 The gas is heavier than air and accumulates in low-lying areas or pockets. It is highly flammable and explosive, in addition to being extremely toxic.

OSHA has regulations and guidelines for workplaces where hydrogen sulfide could be present. These rules apply to confined space entry, where this gas or others can envelop a person and cause death within seconds.

THE GOOD NEWS
Whew! Thank goodness there's some good news to go with this! Hydrogen sulfide gas, in lethal concentrations, doesn't confront most of us everyday like a lot of other life-and-death issues. Like whether to eat a McDonald's hamburger today or not.

HAVE A WONDERFUL HOLIDAY! And while you're having it, every once in a while you might do a little Something to promote PEACE. Even if it's peace in your own heart, because every little bit helps.

Citations

1. Agency for Toxic Substances & Diseases Registry: http://www.atsdr.cdc.gov/Mhmi/mmg114.html
2. http://mattson.creighton.edu/H2S/H2S_Info.html
3. Federal OSHA. www.osha.gov
4. Agency for Toxic Substances & Diseases Registry: http://www.atsdr.cdc.gov/Mhmi/mmg114.html
5. SwopNet Engineering Databank http://www.swopnet.com/engr/Gayman/Gayman_H2S.html
6. Illinois Dept. of Public Health