Hydrogen sulfide is the chemical compound with the formula H₂S. It is a colourless, very poisonous, flammable gas or a colourless liquid at extremely low temperatures or under very high pressure. Hydrogen sulfide has the characteristic foul odour of rotten eggs at very low concentrations. At concentrations between 30-100 ppm, it has a sickeningly sweet odour. The ability to smell it can begin to dull at 50 ppm and may be completely lost.
What is Hydrogen Sulfide used for?
Hydrogen sulfide is used in the manufacture of pulp and paper (as a digesting agent), in tanneries, and in sulfide ores. Most man-made hydrogen sulfide is produced as a by-product of industry rather than for direct industrial use.
Hydrogen sulfide is used in the manufacture of pulp and paper.
Sources and Routes of Exposure
Sources of Emission
Industry sources: Potential large emitters of hydrogen sulfide include
Electric power plants (burning coal or fuel oil containing sulfur)
Oil and gas extraction operations
Oil refineries
Pulp and paper mills
Sewage treatment plants
Large pig farms and other confined animal feeding operations
Portland cement kilns
Municipal waste landfills
Coke ovens
Sulfur products and hydrogen sulfide production
Asphalt production and storage
Geothermal power plants
Most hydrogen sulfide releases are to the air.
Diffuse sources: Other potential emitters include:
Breweries
Fertiliser producers
Glue manufacturers
Processing of ores (Lead, gold, and copper)
Sugar beet and sugar cane processing
Natural sources: Hydrogen sulfide is found in:
Coal pits
Volcanic gases
Natural gas wells
Sulfur springs
Decaying organic matter that contains sulfur
Transport sources:
Found in car exhaust.
Consumer products:
It is not believed that there are any consumer products that contain hydrogen sulfide. However, some products may release hydrogen sulfide—such as septic tanks and the burning of coal or oil.
Routes of Exposure
The primary route of exposure to hydrogen sulfide for both workers and the general population is inhalation. The gas is absorbed rapidly by the lungs. Oral and dermal routes are minor and contribute only a small amount to the overall body burden.
Health Effects
Hydrogen sulfide is both an irritant and a chemical asphyxiant, affecting oxygen utilisation and the central nervous system. Health effects vary depending on the level and duration of exposure. Repeated exposure can cause effects at levels that were previously tolerated.
Low concentrations:
Irritate eyes, nose, throat, and respiratory system
Symptoms include burning/tearing of eyes, cough, and shortness of breath
Asthmatics may experience breathing difficulties
Effects may be delayed for hours or days
Repeated or prolonged exposure may cause:
Eye inflammation
Headache
Fatigue
Irritability
Insomnia
Digestive disturbances
Weight loss
Moderate concentrations:
Severe eye and respiratory irritation
Coughing
Difficulty breathing
Fluid accumulation in the lungs
Headache
Dizziness
Nausea
Vomiting
Staggering
Excitability
High concentrations:
Shock
Convulsions
Inability to breathe
Rapid unconsciousness
Coma
Death (effects can occur with a single breath)
Hydrogen sulfide is not known to cause cancer. The International Agency for Research on Cancer (IARC) has not evaluated its carcinogenicity.
Safety
First Aid Measures
Inhalation: H₂S is extremely flammable and very toxic. Take precautions to ensure your own safety before rescue (e.g., remove ignition sources, wear protective gear, and use a buddy system).
Remove source or move victim to fresh air
If breathing is difficult, trained personnel should administer oxygen
DO NOT allow the victim to move unnecessarily
Symptoms of pulmonary edoema may be delayed up to 48 hours
If breathing has stopped: perform AR, CPR, or AED
Avoid mouth-to-mouth—use shields or guards
Transport victim to emergency care immediately
Victims exposed to ≥500 ppm may release H₂S from clothing, skin, or breath, posing a danger to responders
Gas: If irritated, flush eyes with lukewarm water for 15–20 minutes. Get medical attention immediately
Liquefied gas: Remove victim; briefly flush eyes with lukewarm water. Do not rewarm. Cover both eyes with sterile dressing. Transport victim to emergency care
Note to Physicians:
Amyl nitrite has been suggested as an antidote, though its use is controversial. It may only be effective within the first few minutes and could slow sulfide removal afterwards. If available and safely administered, nitrite therapy may be considered.
Storage
Store cylinders in a well-ventilated, secure area, protected from weather
Cylinders must be upright, with valve seals and caps in place
Keep away from high traffic areas and emergency exits
No ignition sources nearby
Use explosion-proof electrical equipment
Follow National Electrical Codes for Class 1 hazardous areas
Separate flammable storage from oxidisers by at least 20 ft or a 5 ft high fire-rated barrier
Post “No Smoking or Open Flames” signs
Storage temperature must not exceed 125°F (52°C)
Separate full and empty cylinders
Use first-in, first-out inventory method
Install leak detection and alarm systems where possible
Exposure Control & Personal Protection
Engineering Controls
Ventilation:
Install hydrogen sulfide detectors in use/storage areas
Use automatic monitors for oxygen levels and explosive air-gas mixtures
Consider gas cabinets or isolation methods
Ensure natural or explosion-proof ventilation
Prefer local exhaust ventilation to prevent gas spread
Respiratory Protection:
Keep exposure below limits
Use supplied air respirators if limits are exceeded or in emergencies
Follow OSHA 29 CFR 1910.134 or equivalent standards
NIOSH recommendations:
Up to 100 ppm: Use powered air-purifying respirator, gas mask with canister, SAR, or full-facepiece SCBA
Eye Protection
Use safety glasses
Wear face shields if working with liquid H₂S
Ensure eyewash stations and safety showers are nearby
Skin Protection
Wear work gloves when handling H₂S cylinders
Use thermally insulated gloves for liquid H₂S
For chemical use, wear gloves made from:
Butyl rubber
Chlorinated polyethylene
Neoprene nitrile
Polyvinyl rubber
In emergencies, use fire-resistant gloves/clothing
Use double gloves for spills
Other Protective Clothing
Wear appropriate body protection
Use static-resistant clothing
Wear safety shoes when handling cylinders
For high-pressure transfers, wear fire retardant and/or chemically impervious clothing
Regulation
United States
OSHA: The Occupational Safety & Health Administration has set the following permissible exposure limits (PEL) for hydrogen sulfide:
General Industry: 29 CFR 1910.1000 Z-2 Table -- Exposures shall not exceed 20 ppm (ceiling) with the following exception: if no other measurable exposure occurs during the 8-hour work shift, exposures may exceed 20 ppm, but not more than 50 ppm (peak), for a single time period up to 10 minutes.
Construction Industry: 29 CFR 1926.55 Appendix A -- 10 ppm, 15 mg/m3 TWA
ACGIH: The American Conference of Governmental Industrial Hygienists has established the following Threshold Limit Value (TLV) for hydrogen sulfide: 1 ppm, 14 mg/m3 TWA; 15 ppm, 21 mg/m3 STEL
NIOSH: The National Institute for Occupational Safety and Health has set the following Recommended Exposure Limits (REL) for hydrogen sulfide: 10 ppm, 15 mg/m3 Ceiling (10 Minutes)
NIOSH has set a concentration of 100 ppm as IDLH (immediately dangerous to life and health).
Australia
Safe Work Australia: For hydrogen sulfide, it is allowable for workers to be exposed to concentrations of 10 parts per million, averaged over an eight hour workshift, with the exposure not exceeding 15 parts per million.
Australian Drinking Water Quality Guidelines (NHMRC and ARMCANZ, 1996): Aesthetic: Maximum of 0.05 mg/L (i.e. 0.00005 g/L).
United Kingdom
Hydrogen sulfide has a WEL of 5 ppm 8-hour TWA based on data indicating a shift towards anaerobic respiration at exposures to 10 ppm.
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