Hydrogen sulfide

What is hydrogen sulfide?

Hydrogen sulfide (sewer gas) is a colorless gas with the odor of rotten eggs. The odor is detectable at very low concentrations, about 0.0005 parts per million (ppm) to 0.3 ppm. Hydrogen sulfide is produced naturally by decaying organic matter and is released from crude petroleum, natural gas, volcanic gases, liquid manure, sewage sludge, landfills, and sulfur hot springs. Hydrogen sulfide is slightly heavier than air and may accumulate in enclosed, poorly ventilated, and low-lying areas.

Where is hydrogen sulfide used?

Hydrogen sulfide is used in several industries and is a by-product of many industrial processes including oil refining, mining, tanning, wood pulp processing, food processing, craft paper production, and rayon manufacturing.

Hydrogen sulfide is added to natural gas so that residents will notice an unpleasant smell in case of a natural gas leak, since natural gas itself has no odor.

How might I be exposed to hydrogen sulfide?

Inhalation is the major route of hydrogen sulfide exposure for humans. The gas is rapidly absorbed by the lungs. Although it is easily noticed from its strong smell, our noses “get used to” the smell quickly, a process called olfactory fatigue.  This means that if a person does not get away from the source, they can be exposed to dangerous levels without realizing it because they can no longer smell it.

Exposure is most likely for people living or working near certain types of industrial sites, including pulp and paper mills, gas refineries, geothermal power plants, or landfills.

What are the health effects associated with hydrogen sulfide exposure?

The lowest concentration at which some health effects have been observed in asthmatics is at 2 ppm for 30 minutes. Low concentrations of 20-50 ppm cause irritation of the eyes; slightly higher concentrations may cause irritation of the upper respiratory tract. If exposure is prolonged, pulmonary edema may result. As concentrations approach 100 ppm, the odor becomes imperceptible because of olfactory fatigue. At a concentration of 150 ppm, the olfactory nerve is paralyzed. At higher concentrations of 200 to 300 ppm, hydrogen sulfide can be immediately life threatening.

How likely is hydrogen sulfide to cause cancer?

There are no studies that clearly show hydrogen sulfide causes cancer in humans or animals.

How can hydrogen sulfide affect children?

Because hydrogen sulfide is slightly heavier than air and tends to sink, children may be more likely to be exposed to larger amounts than adults in the same situations because they are shorter than adults. Adults and children with asthma may be especially sensitive even to low concentrations of hydrogen sulfide.

Is there a medical test to determine whether I have been exposed to hydrogen sulfide?

In cases of life-threatening hydrogen sulfide poisoning, measurements of blood sulfide or urinary thiosulfate levels may be used to confirm exposure. However, samples need to be taken within two hours of exposure.

What happens to hydrogen sulfide when it enters the environment?

When released into the environment, hydrogen sulfide dissipates into the air and it may form sulfur dioxide and sulfuric acid. Hydrogen sulfide is estimated to remain in the atmosphere for about 18 hours. In some instances it may be released as a liquid waste from an industrial facility.

 

Updated 2021