Hydrogen Sulfide (H2S) Hazards in Construction
Date Posted: 10/27/2023
Hydrogen sulfide is prevalent in natural gas and petroleum. As a result, Workers in gas plants, refineries, petrochemical plants, pulp mills, underground mines, sewers, wastewater treatment plants, and asphalt plants are at high risk of exposure. Hydrogen sulfide (H2S) is a colorless, flammable, extremely hazardous gas with a “rotten egg” smell. Some common names for the gas include sewer gas, stink damp, swamp gas, and manure gas. It occurs naturally in crude petroleum, natural gas, and hot springs. In addition, hydrogen sulfide is produced by the bacterial breakdown of organic materials and human and animal wastes (e.g., sewage).
How Can You Get Exposed to H2S in the Workplace?
Hydrogen sulfide is a mucous membrane and respiratory tract irritant. Immediate or delayed pulmonary edema occurs after exposure to high concentrations. Breathing high levels causes loss of consciousness after one or more breaths and death within a few more breaths. Lower concentrations can result in eye irritation, sore throat and cough, shortness of breath, and lung fluid. Symptoms of acute exposure include nausea, headaches, delirium, disturbed equilibrium, tremors, skin and eye irritation, and convulsions. Inhaling high concentrations can produce rapid unconsciousness and death. You can be exposed to hydrogen sulfide gas primarily by breathing it. However, you also can be exposed to hydrogen sulfide gas through skin and eye contact. According to WAC 296-841-20025, the exposure limits of H2S are ten (10) parts per million (PPM) over an 8-hour time-weighted average (TWA) and 15 parts per million (PPM) over a 15-minute exposure period.
Hazards of H2S Exposure
Exposure above the permissible exposure limit (PEL) quickly results in loss of consciousness and potentially death. Long-term exposure to lower levels results in H2S passing through the lungs and bloodstream. If the body cannot oxidize all the inhaled toxins, H2S builds up in the blood, and the person will eventually asphyxiate.
H2S can be smelled at low levels, but with continuous low-level exposure or higher concentrations, you lose your ability to smell the gas even though it is still present. Likewise, your ability to smell the gas can be lost instantly at high concentrations.
Hydrogen sulfide is a highly flammable, explosive gas that can cause life-threatening situations if not properly handled. In addition, hydrogen sulfide gas burns and produces other toxic vapors and gases, such as sulfur dioxide.
In addition to exposure to hydrogen sulfide in the air, exposure to liquid hydrogen sulfide can cause "blue skin" or frostbite. If clothing becomes wet, avoid ignition sources, remove it, and isolate it in a safe area to evaporate.
The effect called knockdown (rapid unconsciousness) often results in falls that can seriously injure the worker.
How Can You Protect Yourself from H2S Exposure in the Workplace?
Before entering areas where hydrogen sulfide may be present:
Air must be tested for the presence and concentration of hydrogen sulfide by a qualified person using air monitoring equipment, such as hydrogen sulfide detector tubes or a multi-gas meter that detects the gas. Testing should also determine if fire/ explosion precautions are necessary.
It is a best practice to mark work areas where H2S gas may be present clearly. In addition, all workers should be trained on H2S gas and what processes in their work areas produce it.
Any low-lying areas, confined spaces, or any other areas where H2S could be present should be tested for H2S before any worker enters the area.
If the gas is present, the space/area must be ventilated to remove the gas.
If the gas cannot be removed, the person entering the space/area must use appropriate respiratory protection and any other necessary personal protective equipment, rescue, and communication equipment.
A concentration over 100 ppm is considered immediately dangerous to life and health. Therefore, these environments should be avoided. If it is necessary to enter to complete work, there are additional precautions that must be taken, such as using an air-supplying respirator and having stand-by employees that can provide emergency rescue.
Resources
WAC Permissible Exposure Limits (PEL) for Airborne Contaminants
