The H2S Training and Education Center

Learn about H2S

"One of the leading causes of death associated with exposure to hazardous chemicals"

This is a brief summary about H2S, Hydrogen Sulfide, and is not intended to replace our high quality H2S training. The H2S Training and Education Center recommends training if you have found yourself here.

H2S or Hydrogen Sulfide, is a flammable, colorless, and extremely toxic gas with a smell that has been described as smelling like "rotten eggs". H2S is made up of 1 sulfur atom, and two hydrogen atoms. The formation of Hydrogen Sulfide is typically from the bacterial decay of organic material in the absence of oxygen, occurring naturally in; volcanic gases, crude oil, natural gas, some well waters, and in a variety of geological formations. H2S is also a product of many industrial processes including but not limited to; refining, natural gas production, the Kraft pulping process, and many others. H2S is also referred to as sewer gas, stink damp, rotten egg gas, and sour gas.

Properties

• Density

Hydrogen Sulfide is heavier than air, and will collect in low-lying areas such as; basements, manholes, sewer lines, and other enclosed and poorly ventilated areas such as confined spaces. The primary path of exposure is inhalation, where the gas is rapidly absorbed by the lungs.

• Odor

Hydrogen Sulfides characteristic "rotten egg" smell may be evident at low concentrations in the air. However, high concentrations and continuous exposure to low concentrations can cause a person to lose their ability to smell the gas even though it is still present. This condition is known as olfactory fatigue, and can happen rapidly. Olfactory fatigue can occur instantaneously leaving you defenseless against the hazard. For this reason it is NEVER SAFE to rely on your sense of smell to indicate the presence of H2S gas. Death has been reported from continuous exposure to levels as low as 50ppm. To put the measurement ppm into perspective, 1000ppm is only 1% by volume in the air.

• Color

H2S is a colorless gas, and as such has no visual warning signs to indicate its presence.

• Solubility

Hydrogen Sulfide is slightly soluble in water and acts as a week acid. This solution is referred to as sulfurhydric acid, or hydrosulfuric acid. A Hydrogen Sulfide water solution is initially clear, but slowly becomes cloudy over time. With a disturbance H2S can quickly come out of solution, and create hazardous atmospheric conditions where you could be present. H2S can be in solution with mud from excavation sites, or oil and gas drilling operations.

• Flammability

Hydrogen Sulfide is highly flammable, and at higher concentrations is also explosive. The temperature at which H2S will spontaneously ignite is roughly 518F. The tip of a cigarette burns at roughly 700F. When Hydrogen Sulfide is burned, it produces Sulfur Dioxide, which is another hazardous gas.

• Corrosive

Hydrogen Sulfide is corrosive, producing iron sulfite in many industrial processes. Iron sulfite can spontaneously combust in air, and the corrosive action that produces it weakens materials like pipes, vessels, and valves used to contain Hydrogen Sulfide. As iron sulfite is formed, hydrogen is infused into the metals lattice structure, causing weak points in the material. This can lead to sulfide stress corrosion cracking.

In addition to H2S absorbing in the lungs through breathing, Hydrogen Sulfide can also be absorbed through ingestion from contaminated food or water. Once H2S has entered the body it is rapidly distributed to various organs including the lungs, liver, muscle tissue, and the brain. H2S in the brain disrupts the ability to control breathing, and death can occur shortly after.

OSHA Permissible Exposure Limit (PEL)

For General Industry the OSHA PEL is 20ppm for an 8 hour period. This ratio is known as a time weighted average (TWA). Exposure may exceed 20ppm, but no more than 50ppm for a single time period up to 10 minutes.

The IDLH (Immediately Dangerous to Life and Health) Concentration has been set at 100ppm.

The Industry Standards where H2S is typically present establish the safe 8 hour TWA at 10ppm with a peek exposure at 15ppm. No Exposure to Hydrogen Sulfide is really safe though.

Toxicity

Everyone is different, and some people could experience these symptoms at lower levels than what is specified here. H2S can kill you from an acute exposure to high concentrations, or potentially even from chronic exposure to lower concentrations. This list is presented as a guideline

• 0.47 parts per billion (ppb): Odor Threshold
• 0.47 parts per million (ppm): Recognition Threshold, the point at which you will recognize the presence of Hydrogen Sulfide. But remember, it will soon deaden your sense of smell
• 10.0 ppm: Eye irritation begins to occur
• 27.0 ppm: Strong odor, but still tolerable
• 50-100 ppm: Slight respiratory tract irritation within 1 hour, eye damage may occur.
• 100-200 ppm: Eye irritation to the point of pain, inability to smell, coughing, altered respiration, drowsiness, and potentially death
• 320-500ppm: Leads to pulmonary edema with a high possibility of death
• 550-800 ppm: Causes stimulation of the central nervous system and rapid breathing, leading to death
• 800-1000 ppm: Is certaintly deadly with exposure lasting longer than 5 minutes
• >1000 ppm: Instant collapse and respiratory paralysis, death within moments

Hydrogen sulfide can be found virtually anywhere, the most common occurrences are from industrial activities. These activities include but are by no means limited to; Petroleum drilling and refining, wastewater treatment, coke ovens, tanneries, pulp and paper mills, Natural gas drilling and processing, as well as many others. Hydrogen Sulfide also occurs naturally all around the world.

Protecting yourself against H2S exposure

Understanding and utilizing safe work practices when H2S is present is an in-depth subject, and the best way to ensure you're safety is to have the proper training. This section will mention a couple of concepts and list what you should do before entering an area where H2S may be present.

H2S Safe Work Practices

1. Always use the Buddy System
2. Establish Engineering Controls
3. Ensure a Contingency Plan is in place
4. Always work upwind of H2S
5. Be familiar with the appropriate gas detection equipment
6. Use and understand how to use the appropriate PPE (Personal Protective Equipment)
7. Most Importantly, GET QUALITY H2S TRAINING

Before Entering an area where H2S may be present

1. Air must be tested for the presence of H2S Gas, as well as the concentration if the gas is present.
2. Air testing should also determine if fire or an explosion risk is present, and whether or not explosion precautions are necessary.
3. If H2S gas is present, the space or area must be continuously ventilated until the gas level is within acceptable limits, or removed completely.
4. If the H2S gas cannot be removed, appropriate respiratory protection and any other necessary personal protective equipment must be worn by personnel entering the space or area. This includes escape communication equipment, should the individual be overcome by exposure the H2S.

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