About Hydrogen Sulfide (H2S)

This is a brief summary about Hydrogen Sulfide (H2S). For more detailed knowledge through training, please see our H2S Training Solutions.

What is H2S?

H2S or Hydrogen Sulfide is a flammable, colorless, and extremely hazardous gas with a smell that has been described as smelling like "rotten eggs". H2S is also referred to as sewer gas, stink damp, rotten egg gas, sour gas, hydro sulfuric acid, sulfur hydride, sulfane, sulfuretted hydrogen, and hydro sulfuric acid. Hydrogen Sulfide is produced from the bacterial decay of organic material in the absence of oxegen, occurs naturally in volcanic gases, crude oil, natural gas, and in some well waters, and is produced in many industrial activities.

Hazardous properties of Hydrogen Sulfide (H2S) gas

Hydrogen Sulfide is heavier than air, and will collect in low-lying areas such as; basements, manholes, sewer lines, and other enclosed poorly ventilated areas such as confined spaces. However, this does not mean that the only risk of exposure is in these places. Exposure can occur any where H2S gas is present. The primary path of entrance into the body is inhalation, where the gas is rapidly absorbed by the lungs. The Charecteristic "rotten egg" smell may be evident at low concentrations in the air. However, high concentrations and coninuous exposure to low concentrations can cause a person to lose thir ability to smell the gas even though it is still present. This condition is known as olfactory fatigue and can happen rapidly, the ability to smell the gas may even be lost instantaneously. For this reason it is NOT SAFE to rely on your sense of smell to indicate the presence of H2S gas. Death has been reported with continuous exposure to levels as low as 50 ppm. Hydrogen Sulfide can also be absorbed through ingestion by contaminated forrd, or through skin via water and air. Once H2S has entered the body it is rapidly distributed to various organs, including the lungs, liver, muscle tissue, and nervous system. H2S is also flammable, and at certain concentrations explosive. If ignited the gas burns to produce other toxic gases such as sulfur dioxide. Another byproduct of many prodution operations is Iron Sulfite, which may spontaneously combust in air. This byproduct is created by the corrosion of materials used in production facilities where hydrogen sulfide is present.

Health Effects

• 0.47 ppb, Odor threshold
• 0.47 ppm, Recognition threshold
• 10.0 ppm, Eye irritation begins to occur
• 27.0 ppm, Strong odor, but still tolerable
• 50-100 ppm, Slight repiratory tract irritation within 1 hour, eye damage may occur
• 100-200 ppm, Eye irritation to the point of pain, loss of sense of smell, coughing, altered respiration, drowsiness
• 320-550 ppm, leads to pulmonary edema with high potential for death
• 550-800 ppm, causes stimulation of the central nervous system and rapid breathing, leading to death
• 800-1000 ppm, deadly within 5 minutes of exposure
• >1000 ppm, imediate collapse and respiratory paralysis, death within moments

With many of these exposure levels, repiratory paralysis and death may occur instantly, or within 72 hours of an acute exposure at high levels, or chronic exposure at lower levels.

Where is H2S Gas?

Though Hydrogen Sulfide can be found virtually anywhere, the most common occurrences are from industrial activities. These activities include but are not limited to: Petroleum drilling and refining, Natural gas drilling and processing, wastewater treatment, coke ovens, tanneries, pulp and paper mills, and many others.

Protecting yourself against H2S exposure

The number one way to ensure you're safety is to have proper training. Click Here to see our training offerings.

Before entering an area where H2S may be present, the following precautions must be taken:

• Air must be tested for the presence of H2S gas, as well as the concentration if the gas is present. This action should be performed by a qualified person using air monitoring equipment, such as a multi-gas meter capable of detecting Hydrogen Sulfide.
• Air testing should also determine if fire or explosion risk is present, and whether or not explosion precautions are necessary.
• If the H2S gas is present, the space or area must be coninuously ventilated until the gas level is within acceptable limits, or removed completely.
• If the gas cannot be removed, appropriate respiratory protection and any other necessary personal protective equipment (PPE) must be worn by the person entering the space or area, this includes escape and communication equipment should the individual become incapacitated.

OSHA Permissible Exposure Limit (PEL) for H2S gas

• 20 ppm, maximum ceiling threshold.
• 50 ppm, maximum peak above ceiling threshold. This level is for only 10 minutes, once per 8 hour shift, and only if there is no other measurable exposure.

(Note: There have been suggestions and recommendations to lower the 20 ppm PEL, to 10 ppm as even a reading below 10 ppm may potentially be dangerous, and cannot guarantee your safety.)

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