Every year, some sewer workers, farmers, construction workers and others die from exposure to hydrogen sulfide (H2S).
Why should this be? The hazards are well known. A whole industry has grown up around protecting people about this and other toxic gases. There’s confined-space entry training. There are confined-space safety systems that include gas detectors, tripods with winches, respirators and other gear.
Why should anyone ever be exposed to harmful amounts of this gas? Well, it’s because either they don’t know the risks or they ignore the warnings. So it’s worthwhile to revisit the dangers of H2S, and especially to share the information with new people coming into the drain and pipe maintenance profession.
Know the basics
OSHA provides extensive information about H2S. Here are some facts and cautionary advice taken from an H2S fact sheet.
H2S is a colorless, flammable, extremely hazardous gas that has a rotten egg smell. It is sometimes called sewer gas, stink damp, swamp gas, or manure gas. It comes from bacterial breakdown of materials like manure and sewage.
H2S is heavier than air and collects in low-lying, enclosed and poorly ventilated areas, including manholes and sewer lines. The primary route of exposure is inhalation; the lungs absorb the gas rapidly.
You can smell H2S at low concentrations, but after continuous exposure, you lose your ability to smell the gas (this is called olfactory fatigue). At high concentrations, olfactory fatigue can occur almost instantly. Therefore, never rely on your sense of smell to indicate whether H2S is present or to warn of high levels.
Effects on health
H2S is both an irritant and a chemical asphyxiant. It affects oxygen utilization and the central nervous system. Its effects can vary depending how much you are exposed to and for how long. Low concentrations irritate the eyes, nose, throat and respiratory system – you may experience burning or tearing of the eyes, coughing, or shortness of breath. People with asthma may have trouble breathing.
The effects can be delayed for several hours, or sometimes several days, when you work in low concentrations. Repeated or prolonged exposures may cause eye inflammation, headaches, fatigue, irritability, insomnia, digestive disturbances and weight loss. Moderate concentrations can cause more severe eye and respiratory irritation (coughing, difficulty breathing, fluid in the lungs), as well as headaches, dizziness, nausea, vomiting, staggering and excitability.
High concentrations can cause shock, convulsions, inability to breathe, extremely rapid unconsciousness, coma and death. Effects can occur within a few breaths and possibly a single breath.
Protecting yourself
Before you enter an area where H2S may be present, the air must be tested for its presence and concentration by a qualified person, using equipment such as H2S detector tubes or a multi-gas meter. Testing should also determine if fire or explosion precautions are also necessary. If the gas is present, the space must be ventilated continually.
If the gas cannot be removed, the person entering the space must use appropriate respiratory protection and any other necessary personal protective equipment, as well as rescue and communication equipment. The OSHA confined spaces standard contains specific requirements for identifying, monitoring and entering confined spaces.
OSHA has determined that a level of H2S gas at or above 100 parts per million is immediately dangerous to life and health (IDLH). Entry into IDLH atmospheres can only be made using a full-facepiece, pressure-demand, self-contained breathing apparatus (SCBA) with a minimum service life of 30 minutes, or a combination full-facepiece, pressure-demand, supplied-air respirator with an auxiliary self-contained air supply.
If the H2S level is below 100 ppm, an air-purifying respirator may be used, assuming the filter cartridge/canister is appropriate for H2S. A full-facepiece respirator will prevent eye irritation.
If air concentrations are elevated, eye irritation may become a serious issue. If a half-mask respirator is used, tight-fitting goggles must also be used. Workers in areas containing H2S must be monitored for signs of overexposure.
And finally, OSHA warns that no one should attempt a rescue in an area that may contain H2S without using appropriate respiratory protection and without being trained in such rescues. The likely result of attempting a rescue while untrained and ill-equipped is a multiple fatality.
