Hydrogen Sulfide

Evaluating and Controlling Exposure

Example of a portable meter that can measure hydrogen sulfide.
Example of a portable meter that can measure hydrogen sulfide.

Used with permission from PETEX®, The University of Texas, Austin. All rights reserved©
PETEX 2001.

Follow OSHA requirements for confined space entry. Enter the space only if necessary and follow established procedures:

  • Test (monitor) the air in the space from the outside before entering.
  • Test (monitor) the air in the space continuously during work operation.
  • Determine if entry permit is required.
  • Ventilate area continuously to remove accumulated hydrogen sulfide.
  • Make sure that rescue procedures, personnel, and equipment (e.g., positive pressure SCBAs) are in place.
  • Maintain contact with trained attendant.

See also: Permit-Required Confined Spaces in General Industry. OSHA QuickCard™. Explains what workers should do before entering a confined space, such as underground vaults, tanks, storage bins, silos or manholes based on the requirements of OSHA's Standard for Permit-required Confined Spaces [29 CFR 1910.146].

A sign warning workers of hydrogen sulfide hazards.
A sign warning workers of hydrogen sulfide hazards.

Used with permission from PETEX®, The University of Texas, Austin. All rights reserved© PETEX 2001.

Self-contained breathing apparatus (SCBA).
Self-contained breathing apparatus (SCBA).

Used with permission from PETEX®, The University of Texas, Austin. All rights reserved© PETEX 2001.

To protect workers from harmful hydrogen sulfide exposures:

  • Evaluate exposure to know whether H2S gas is present and at what levels.
  • Eliminate the source of hydrogen sulfide whenever possible.
  • If the source cannot be eliminated, control exposures by:
    • Using engineering controls as the next best line of defense.
    • Developing administrative controls and safe work practices to reduce exposures to safe levels.
  • Use personal protective equipment if engineering controls and work practices alone cannot reduce hydrogen sulfide to safe levels.
Evaluate Exposure
  • Identify processes that could release or produce hydrogen sulfide. This includes identifying known sources of hydrogen sulfide and evaluating possible fire and explosion hazards. Use a Process or Job Hazard Analysis for identifying and controlling hazards.
  • Test (monitor) the air for hydrogen sulfide. This must be done by a qualified person. Use the right test equipment, such as an electronic meter that detects hydrogen sulfide gas.

    Conduct air monitoring prior to and at regular times during any work activity where hydrogen sulfide exposure is possible. When working in confined spaces air monitoring must be conducted in accord with the applicable OSHA standards. Detector tubes, direct reading gas monitors, alarm only gas monitors, and explosion meters are examples of monitoring equipment that may be used to test permit space atmospheres.

  • Procedures for Atmospheric Testing in Confined Spaces. OSHA Fact Sheet. Discusses the importance of evaluating the hazards of the confined space and verifying that acceptable conditions exist for entry into that space.

Information on general atmospheric testing methods:

  • OSHA Occupational Chemical Database. OSHA's premier one-stop shop for occupational chemical information. It compiles information from several government agencies and organizations. Information available on the pages includes chemical identification and physical properties, exposure limits, sampling information, and additional resources.
  • NIOSH Method 6013. Air samples are collected with a glass tube and personal sampling pump and analyzed with ion chromatography.

DO NOT rely on your sense of smell to indicate the continuing presence of hydrogen sulfide or to warn of harmful levels. You can smell the "rotten egg" odor of hydrogen sulfide at low concentrations in air. But after a while, you lose the ability to smell the gas even though it is still present (olfactory fatigue). This loss of smell can happen very rapidly and at high concentrations and the ability to smell the gas can be lost instantly (olfactory paralysis).

Control Exposures
  • Use exhaust and ventilation systems to reduce hydrogen sulfide levels. Make sure that the system is:
    • Non-sparking
    • Grounded
    • Corrosion-resistant
    • Separate from other exhaust ventilation systems
    • Explosion-proof

    These safety measures are important because hydrogen sulfide is flammable and can corrode materials if they are not properly protected. When working in confined spaces ventilation should operate continuously and must be conducted in accord with the applicable OSHA standards.

  • Train and educate workers about hazards and controls. Training topics may include:
    • Characteristics, sources and health hazards of hydrogen sulfide
    • Symptoms of hydrogen sulfide exposure
    • Types of hydrogen sulfide detection methods and applicable exposure limits
    • Workplace practices and procedures to protect against hydrogen sulfide exposure
    • Emergency plans, locations of safety equipment, rescue techniques, first-aid
    • Confined space procedures
  • Establish proper rescue procedures to safely rescue someone from a hydrogen sulfide exposure.

    WARNING: First responders must be trained and properly protected before entering areas with elevated levels of hydrogen sulfide.

    Rescuer protection should include:

    • Positive-pressure, self-contained breathing apparatus (SCBA).
    • A safety line to allow for rapid exit if conditions become dangerous.
  • Use respiratory and other personal protective equipment. If engineering and administrative controls cannot reduce hydrogen sulfide below OSHA's permissible exposure limit, employers must provide respiratory protection and other personal protective equipment (PPE), such as eye protection and possibly fire-resistant clothing. Employers must complete a PPE hazard assessment and equipment selection process in accord with the OSHA regulations before beginning any work activities. Respiratory protection should be at least:
    • 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) with a minimum service life of thirty minutes or a combination full face pressure demand supplied-air respirator with an auxiliary self-contained air supply. Exposures at or above 100 ppm are considered immediately dangerous to life and health (IDLH).
  • Whenever respirators are used, the employer must have a respiratory protection program that meets the requirements of OSHA's Respiratory Protection standard (29 CFR 1910.134). This program must include proper respirator selection, fit testing, medical evaluations, and training. For more information on respiratory protection see:

    Refer to Other Resources for more information about controlling hydrogen sulfide exposures in specific industries and operations.