Hydrogen sulfide in the oil and gas industry
Hydrogen sulfide formation
Hydrogen sulfide (H2S) is an extremely hazardous gas that is colorless, flammable, soluble in water, and smells like rotten eggs. It occurs naturally in crude petroleum and natural gas and can be produced by the breakdown of organic matter and human waste (e.g., sewage).
It is heavier than air and can collect in low-lying and enclosed, poorly ventilated areas such as basements, manholes, sewer lines, and underground telephone/electrical vaults. H2S can be detected by its scent at low levels, but with continuous low-level exposure or at higher concentrations, you lose your ability to smell the gas even though it is still present.
At high concentrations, your ability to smell the gas can be lost instantly. Hydrogen sulfide is known as “The Silent Killer.” Everyone involved in company operations has certain responsibilities concerning H2S safety and compliance measures.
Responsibility of companies and employees
Company responsibilities include:
- Protecting workers from H2S exposure.
- Identifying H2S Hazards.
- Providing appropriate annual training to all workers.
- Establishing safe work practices relating to H2S.
- Monitoring levels of H2S throughout the workplace or locations.
- Providing proper PPE specifically designed to shield workers from the effects of H2S.
- Performing a check for ignition sources in the area before starting any potentially hazardous work.
- Providing at least one worker who is qualified to perform first aid and CPR for H2S victims.
- Attending yearly training and safety meetings.
- Using controls and following safe work practices.
- Using required PPE and personal monitors.
- Reporting exposure incidents.
- Using SWA when necessary.
- Making sure that work areas, vents, and purge lines are functioning and ventilated before work begins.
Sources of hydrogen sulfide
H2S does occur naturally and it may be produced during industrial processes. H2S is produced in nature primarily through the decomposition of organic material by bacteria.
Areas in nature where this can occur are within low oxygen environments such as swamps and polluted water. H2S also forms as a part of natural gas, petroleum, crude oil, sulfur deposits, volcanic gases, and sulfur springs. Sour crude oil refers to oil that contains 0.05% sulfur.
Depending on what your job is in this industry, you need to be aware of all of the possibilities of exposure when performing your job duties. Some examples include the shale shaker area, circulation fluid treatment areas, during tripping procedures, at the wellhead, at the cellar, and on the drilling floor.
H2S exposure is a major concern in the petroleum industry, especially at oil and natural gas wells, in refineries, natural gas plants, and at pipelines.
You may see H2S listed in chemical manuals as sulfuretted hydrogen, hydrogen sulfide, hydro sulfuric acid, or dihydrogen sulfide. Due to its toxicity, the EPA has classified H2S as hazardous waste. Concentrations of H2S are measured in parts per million (ppm) or percentages.
H2S is highly toxic and if inhaled, can have a severe effect on one’s health. It is 19% heavier than air and collects in low-lying areas and confined spaces. It is highly flammable may spontaneously ignite at high temperatures, causing an explosion. H2S is almost always in gas form, meaning it will be invisible to you.
H2S reacts with strong oxidizers, bleach, and hydrogen peroxide to cause fire, explosions, or metal damage. It produces toxic SO2 gas when burned. It forms metal sulfides that could spontaneously ignite when exposed to air. When it is dissolved in water, it forms a weak acid that corrodes metals such as steel, carbon steel, copper, silver, brass, and bronze.
Exposure to hydrogen sulfide
Exposure to H2S can occur through inhalation or skin contact. The most dangerous type of exposure to your health is inhalation, which at high levels can cause death. Skin absorption is a concern when exposed to compressed liquid. 10 ppm is the industry-accepted exposure level.
If you inhale H2S, the chemical affects your eyes, nose, brain, lungs, and the nerve pathways that connect. H2S impairs the part of your brain that controls your breathing, and it can cause you to stop breathing depending on the gas concentration and how long you have been exposed.
- At 1 ppm, you may be able to smell the H2S odor, a “rotten egg” smell.
- At 10 ppm, your eyes and airways become irritated after an hour of exposure.
- At 20 ppm, headaches, nausea, vomiting, coughing, and difficulty breathing may occur.
- At 50 ppm, your sense of smell is eliminated after 15 minutes of exposure.
- At 100 ppm, loss of smell occurs after 3 minutes of exposure, and eye and respiratory tract irritation occur.
- At 200 ppm, the sense of smell is eliminated almost immediately, and you will experience a burning sensation in your eyes and nose.
- At 500 ppm, unconsciousness occurs after brief exposure and the victim will not be able to breathe if they are not treated quickly.
- At 700 ppm, unconsciousness occurs instantly, breathing stops, and the victim will die if not rescued right away.
- At 1,000 ppm, instant unconsciousness and permanent brain damage occur, leading to death.
Depending on your overall health, exposure to H2S may make you more sensitive to its effects. Smoking, drinking alcohol, or taking prescription medications or illicit drugs can affect what happens when exposure occurs. If you have been repeatedly exposed, it may make you more sensitive to the effects of H2S.
Safety processes to combat the risk of hydrogen sulfide
Properly communicating the hazards of hydrogen sulfide is extremely important. OSHA requires warning signs to mark areas contaminated with H2S. Each warning sign corresponds to the concentration of H2S that could occur in the area. They are color-coded so that you can determine the level of hazard that is classified by API conditions.
- A ‘no hazard’ condition does not require a flag.
- API Condition I is a low hazard. H2S ppm is less than 10 and the H2S detector flag color will be green. Safety equipment needs to be readily accessible.
- API Condition II is a medium hazard. H2S ppm could be between 10 and 30 and the H2S detector flag color will be yellow. Audible and visual alarms must be in place, safety equipment must be readily accessible, and an oxygen resuscitator must be preset.
- API Condition III is a high hazard.
Companies use engineering controls as the first defense in protecting employees from H2S. Companies work from a long list of controls to keep you from being exposed to high concentrations of H2S. Most operations use local exhaust or natural ventilation to control the amount of H2S that is released into the air. Burning and flaring vent lines are used when H2S could be present in concentrations over 15 ppm.
Administrative controls consist of proper work procedures and practices that lower the risk of being exposed to H2S. Having proper procedures in place and conducting the appropriate training can reduce workplace accidents, and doing so should be a top goal for every administration.
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