How to Protect Against the Dangers of High Concentrations of Hydrogen Sulfide (H2S)

Safety professionals stress the importance of a plan for protecting workers from high concentrations of hydrogen sulfide (H₂S). Many industries use the natural gas in the manufacturing process. Others create H₂S as a by-product of their processes.

When workers aren’t protected properly from high concentrations of H₂S, they can suffer health effects ranging from insomnia to death.

According to the Agency for Toxic Substances & Disease Registry, H₂S is most prevalent in

• The petroleum industry
• Mining
• Rayon manufacturing
• Pulp and paper mills
• Food processing
• Sewage treatment plant

Low, confined spaces cause problems with H₂S for individual workers. Hydrogen sulfide is heavier than air, allowing it to travel across and fill low areas like basements, manholes, sewers, and manure pits. Also called dihydrogen sulfide, sewer gas, stink damp, and sour gas, H₂S is flammable and highly toxic.

Adverse Health Effects of High Concentrations of the Natural Gas

The experts at the Centers for Disease Control (CDC) warn that both acute and chronic exposure to H₂S are highly dangerous. One exposure to high levels of hydrogen sulfide can cause immediate death. In other cases, health problems might not show up until three days after the exposure.

People who have continuous low-level exposure may report low blood pressure, loss of appetite, chronic cough, weight loss, and many other systems, according to the CDC.

Like the deadly gas hydrogen cyanide, we’ve all heard of, high levels of hydrogen sulfide attack the body by inhibiting cellular respiration. Victims may have various respiratory symptoms, experience convulsions, or suffer rapid unconsciousness. In a worst-case scenario, a victim’s organs and nervous system shut down leading to an immediate collapse.

In acute instances, treatment depends on how long the person is exposed, the level of gas present in the air, and how the person was exposed. Doctors also will consider other chemicals the person is exposed to, their overall health, age, lifestyle, and other predictors of overcoming the effects of exposure to H₂S.

Health Problems Increase with High Levels of H₂S Exposure

To protect workers from health problems, OSHA has regulations for permissible exposure limits for chemical compounds. The limit for H₂S is 20 parts per million (ppm).

• Effects of exposure to low levels: The effects of inhaling low levels of H₂S (10 ppm or less) may include a burning sensation in the eyes, coughing, and shortness of breath. Repeated or continuous exposure at low concentrations can cause eye inflammation, headaches, fatigue, irritability, insomnia, and weight loss.
• Exposure to moderate levels: Exposure to a concentration of hydrogen sulfide between 10 and 100 ppm can result in severe eye irritation, tearing of the eyes, severe respiratory tract irritation (coughing, difficulty breathing, fluid in lungs), loss of smell, headache, nausea, vomiting, and staggering.
• Exposure to high concentrations: Lethal concentrations occur at 100 ppm or higher. Individuals may experience shock, convulsions, pulmonary edema, rapid unconsciousness, and coma.
• Skin contact: Direct contact with the liquid form of hydrogen sulfide can cause frostbite.

Beyond Smelling Rotten Eggs: How to Identify the Colorless Gas

Monitoring the air quality at work sites is everybody’s job. Identifying hydrogen sulfide can be challenging because it almost always occurs as a colorless gas. Fortunately, a rotten egg smell often indicates high concentrations of H₂S in the air. However, the odor should not be used to confirm the presence of H₂S because of something called olfactory fatigue. This is when people lose their sense of smell after prolonged exposure. Thus, workers need to be trained to detect excessive H₂S in ways that don’t involve their noses.

Follow best practices for safety professionals by including your employees in monitoring H₂S levels. One tool for gathering input is an easy-to-use online platform offered by HSI. The platform gives workers a place to record what they see, and smell, on job sites and communicate with safety professionals.

In addition to involving your employees, there are several ways you can protect against the main routes of exposure to H₂S:

1. Engineering controls: Use engineering controls such as ventilation systems that remove gas from confined spaces. Since hydrogen sulfide is an explosive gas, the ventilation system must be designed to block toxic gasses flowing from an unexpected blast.
2. Administrative controls: Develop and communicate rules for entering, exiting, and working in spaces where hydrogen sulfide gas is present. Safety training and gas-level testing also are effective administrative controls for occupational health.
3. Use of safety equipment: The primary personal protective equipment when working around H₂S is respiratory protection. Full-facepiece respirators are used for gas amounts up to 100 ppm. Self-contained breathing apparatuses, or supplied air lines, protect workers when gas levels are between 100 and 1,000.
4. PPE for handling liquid H₂S. Workers who handle canisters of H₂S need to wear protective gloves and clothing. Manufacturers and safety equipment suppliers will recommend specific protective clothing for your operations.

First Aid for H₂S Exposure

Planning ahead for potential acute exposures to H₂S will help you and your company’s leaders sleep better at night. The HSI course on hydrogen sulfide safety touches on how to manage emergencies from H₂S exposure.

First aid ranges from helping workers with eye irritation to doing CPR. Pay close attention to victims’ eyes, skin, and breathing.

• Eye contact: Remove contact lenses if the victim is wearing them. Wash the victim’s eyes with water for 15 minutes, lifting the eyelids to ensure the water reaches all parts of the eye. Seek immediate medical attention.
• Skin exposure: Wash the victim’s skin immediately. Clothing and shoes exposed to H₂S will be flammable; to reduce the risk of static discharge and ignition, soak contaminated articles of clothing thoroughly while they are still being worn. Remove the clothing, then seek immediate medical attention.
• Shortness of breath from mild inhalation: Get the victim or victims to fresh air. Call 911 or poison control.

In cases of severe inhalation, call 911 immediately. Before trying to help a victim, protect yourself. If possible, follow your company’s non-entry procedures. If you must enter a hazardous space, wear a full-face breathing apparatus, then follow these steps.

• Get the victim to fresh air.
• If a victim has rapid unconsciousness, see if they are breathing. If they are not, start CPR. If the victim is breathing, move them into recovery position to maintain an airway and prevent them from choking.
• If the person’s heart has stopped, or they are not breathing, begin CPR if you are trained.
• First responders will transfer the patient to a hospital immediately.

What to Expect When Fire Erupts

In addition to providing first aid and assessing the extent of injuries, safety professionals assist firefighters when a fire erupts from a hydrogen sulfide explosion. The firefighters will need information about the plant or facility to help them attack the fire. When they arrive on the scene, they will:

• Shut off the source of the hydrogen sulfide emissions if possible.
• Use water spray to extinguish any flames.
• Spray water to cool containers, structures, or equipment exposed to fire.
• Use dry chemicals, foam, and carbon dioxide to extinguish fires if water is not available.

The HSI course Hydrogen Sulfide Safety covers the awareness-level content your team needs. Contact us to learn more about our safety training.

Additional Resources

• Safety Tip Video: Hydrogen Sulfide (H2S) Safety
• Course: Personal Protective Equipment (PPE)