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1. Understanding Hydrogen Sulfide Risks and Preventing Exposure What is it, and where does it come from ? Hydrogen sulfide (H 2 S) is a colorless, highly toxic, corrosive, and flammable gas that has a distinct “rotten egg” smell. It can be present in (sour) crude oil and natural gas, but it can also form from the decomposition of organic material by bacteria. Naturally occurring sulfur reducing bacteria can produce hydrogen sulfide in an anerobic (lacking oxygen) environment from a wide variety of potential sources including sewage, protein based firefighting foams, biodegradable cleaners, and organic material in ballast tanks. H 2 S is heavier than air so it tends to accumulate in low lying areas with poor ventilation. It is highly soluble in oil and slightly soluble in water. Symptoms of exposure to H2S Inhalation of high concentrations of hydrogen sulfide can produce rapid unconsciousness and death. The shipyard 8-hour time weighted average limit for exposure is 10 PPM. The Immediately Dangerous to Life or Health (IDLH) concentration value for H 2 S is 100 PPM. Low concentrations irritate the eyes, nose, throat and respiratory system (e.g., burning/ tearing of eyes, cough, shortness of breath). Moderate concentrations can cause more severe eye and respiratory irritation (including coughing, difficulty breathing, accumulation of fluid in the lungs), headache, dizziness, nausea, vomiting, staggering and excitability. High concentrations can cause shock, convulsions, inability to breathe, extremely rapid unconsciousness, coma and death. Unconsciousness can occur in a matter of seconds followed by death within a matter of minutes. Preventing exposure Test the atmosphere with a gas detector to measure for H 2 S prior to space entry. DO NOT RELY on your sense of smell! At elevated concentrations of H 2 S ( > 100 PPM) your nose will rapidly lose the ability to detect the “rotten egg” odor due to olfactory fatigue. Ventilate the workspace if required. For exposures below 100 ppm, use an air-purifying respirator with specialized canisters/cartridges for hydrogen sulfide. A full face respirator will provide eye protection. For exposures at or above 100 ppm, use a full face pressure demand self-contained breathing apparatus (SCBA) or a combination full face pressure demand supplied-air respirator with an auxiliary self-contained air supply. Toolbox Safety Minute– Hydrogen Sulfide (H 2 S) Responding: H 2 S is highly toxic and can quickly incapacitate you. Don’t go in to rescue someone unless you have a self-contained breathing apparatus (SCBA) or you could also become a victim.

2. Toolbox Safety Minute– Hydrogen Sulfide (H 2 S) Fish Holds Hydrogen sulfide can form in fish and fish product holds by the decomposition of organic material. Testing is necessary to ensure the permissible exposure limit (PEL) of 10 ppm is not exceeded. The photo below shows H 2 S levels in a fish hold at 41 ppm, making it unsafe to enter. Sewage & Gray Water Tanks Sewage collection and treatment tanks are the classic example of where H 2 S can accumulate onboard a ship. When organic waste is decomposed by bacteria, H 2 S is released in the process. Often overlooked, gray water holding tanks present a similar nutrient rich environment to that of sewage tanks for bacteria to grow and for the potential of H 2 S generation.

3. Toolbox Safety Minute – Hydrogen Sulfide (H 2 S) Oily Waste Storage Tanks In 1985 a leak in an oily waste storage tank on the Australian vessel HMAS Stalwart resulted in release of H 2 S resulting in 3 fatalities and the incapacitation of 60 more sailors. The USCG Safety Alert 08-18 highlights the danger of H 2 S in oily waste and bilge slop tanks. Sulfate reducing bacteria found naturally in seawater can generate H 2 S while in storage. Biodegradable cleaners that end up in the waste serve as a nutrient source for the bacteria increasing the production of H 2 S . Foam Storage Tanks Sulfate reducing bacteria are found naturally in seawater. Foam protection systems typically combine seawater and foam concentrate. Aqueous Film Forming Foam (AFFF) concentrate that has mixed with seawater and remains stagnant for long periods of time can generate H 2 S as the sulfate reducing bacteria breakdown the foam concentrate. Placeholder Photo