Confined Spaces and Hydrogen Sulfide

Hydrogen sulfide is a flammable and toxic gas found particularly in confined spaces such as trenches and sewers. For the construction industry, this poses particular risk for workers in outdoor excavation projects. Specific regulations for confined spaces General Industry are found on OSHA’s website. (29 CFR 1910)

OSHA recently cited a Dallas utility company for failing to protect workers from hydrogen sulfide after an employee died after exposure to dangerous levels of the gas while working in a trench. Inspectors determined that the company exposed employees to a hazardous atmosphere, failed to train employees on the health hazards of hydrogen sulfide, and did not drain water from the trench. The company faces penalties of $422,006.

Employers are required to test the air to detect the presence of the gas, use exhaust systems to reduce hydrogen sulfide levels, train workers on hazards and control methods, and provide personal protective equipment if control methods used are not sufficient to reduce hydrogen sulfide levels.

In general, working in the following areas and conditions increases a worker’s risk of overexposure to hydrogen sulfide:

  • Confined spaces (for example pits, manholes, tunnels, wells) where hydrogen sulfide can build up to dangerous levels.
  • Windless or low-lying areas that increase the potential for pockets of hydrogen sulfide to form.
  • Marshy landscapes where bacteria break down organic matter to form hydrogen sulfide.
  • Hot weather that speeds up rotting of manure and other organic materials, and increases the hydrogen sulfide vapor pressure.

Before entering areas with possible Hydrogen Sulfide:

  • The air needs to be tested for the presence and concentration of hydrogen sulfide by a qualified person using test equipment. This individual also determines if fire/explosion precautions are necessary.
  • If gas is present, the space should be ventilated.
  • If the gas cannot be removed, use appropriate respiratory protection and any other necessary personal protective equipment (PPE), rescue and communication equipment. Atmospheres containing high concentrations (greater than 100 ppm) are considered immediately dangerous to life and health (IDLH) and a self-contained breathing apparatus (SCBA) is required.
  • The primary route of exposure is inhalation and the gas is rapidly absorbed by the lungs. Absorption through the skin is minimal. People can smell the “rotten egg” odor of hydrogen sulfide at low concentrations in air. However, with continuous low-level exposure, or at high concentrations, a person loses his/her ability to smell the gas even though it is still present (olfactory fatigue). This can happen very rapidly and at high concentrations, the ability to smell the gas can be lost instantaneously.
  • In addition, hydrogen sulfide is a highly flammable gas and gas/air mixtures can be explosive. It may travel to sources of ignition and flash back. If ignited, the gas burns to produce toxic vapors and gases, such as sulfur dioxide.

For more safety information and precautionary measures, contact our offices at Diversified Safety Services.

The following two tabs change content below.

Nina McGinley

Latest posts by Nina McGinley (see all)

About Nina McGinley