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Confined Spaces


What is a confined space? Areas such as manholes, storage tanks, pumping stations, and other spaces with limited openings for entry or exit that are not meant to be continuously occupied.

Who is at risk: Workers whose jobs involve street and highways, utilities, public works department, water and wastewater.

Hazards: The air in confined spaces can contain too little oxygen to breathe, or there can be a danger from explosion, fire, or poisonous gases. Chemicals, infectious diseases, and safety hazards can also be present.

Prevention: Checking for possible explosive and fire hazards in the air, using ventilation to provide air that is safe to breathe, using protective equipment, and being ready to make a safe rescue.

Laws: The text of OSHA's Permit-required confined spaces standard, 29 CFR 1910.146, is available on the internet.


What is a confined space?

A confined space is an area that:

  • has limited openings for entry and exit,
  • has poor natural ventilation that can pose serious risks, and
  • is not designed for continuous occupancy by workers.

Examples of confined spaces include, but are not limited to:

  • storage tanks,
  • process vessels,
  • pits, vats, and vaults,
  • sewage digesters and sewer silos,
  • tunnels, manholes, utility vaults,
  • pumping stations and enclosed grit chambers.

Entry into confined spaces may be for the purpose of inspection, testing of equipment, repair, maintenance and cleaning, or an emergency.

Who is at risk?

Workers in public works departments, water and wastewater, street and highways, utilities and others perform tasks in confined spaces.

What are the hazards in confined spaces?

Hazards in the Air within Confined Spaces (Atmospheric)

  • Oxygen-deficient means that there is not enough oxygen in the space to safety breathe. Normal air is made up of 20.8 percent oxygen compared to less than 19.5 percent in an oxygen-deficient atmosphere. Air that has less than 10 percent oxygen can cause unconsciousness and levels below 8 percent can quickly cause death.
  • Oxygen-enriched means there is too much oxygen. Air with over 23.5 percent oxygen can cause clothing, hair, and other flammable materials to burn violently when ignited.
  • Flammable atmospheres are caused by a mixture of dusts, gases or vapors that can explode or catch fire. The mixture cannot burn if there is not enough fuel (lean), or if there is too much fuel (rich).
  • Toxic gases and vapors come from a wide variety of sources. Carbon monoxide, hydrogen sulfide, and methane are three of the most common and deadly gases that are naturally produced in confined spaces.
    • Carbon Monoxide has no odor or color. Too much carbon monoxide in the air prevents workers from being able to breathe oxygen. Carbon monoxide is a combustible gas that gets into the air when machines do not completely burn gas, oil and other fossil fuels.
    • Hydrogen Sulfide has no color but does have a strong "rotten egg" odor. Hydrogen sulfide is flammable and is created by the decay of organic matter that is found in sewers and sewage treatment plants.
    • Methane has no color or odor. In addition to causing explosions, as methane builds up it moves out breathable air and can cause suffocation.

Chemical, Physical, and Biological Hazards in Confined Spaces

  • Toxic chemicals are sometimes present in confined spaces. For example, chemicals from industrial plants, or pesticides from farms or lawn use, or other sources can end up in the confined spaces in water treatment facilities. Welding can produce dangerous fumes.
  • Physical and safety hazards in confined spaces include but are not limited to too much noise, falls, becoming stuck in a tight spot, or being buried by material stored in the space.
  • Biological hazards in confined spaces come mainly from contaminated water in the area. Diseases that workers can get from work include, but are not limited to hepatitis, leptospirosis (Weil's Disease) staphylococci, salmonella, E. coli, and parasites.

What is the difference between a "permit-required" and a "non-permit-required" confined space?

The employer is required to determine if there are any confined spaces that present or could pose a hazard in the workplace. Confined spaces are of two types, permit-required or non-permit required.

permit-required confined space has any of these dangers:

  • a dangerous or potentially hazardous atmosphere,
  • contains material that could bury (engulf) workers,
  • has a shape that could cause workers to be trapped, or
  • has any other recognized serious health hazards.

non-permit required confined space is an area that does not contain any hazards capable of causing death or serious physical harm. Employers must make sure that there are no atmospheric or other major dangers.

What must be done to protect workers in confined spaces?

  • Monitoring the air in the confined space BEFORE entry: The air in a confined space must be checked for dangerous conditions before workers enter. It is important to monitor at the top, middle and bottom of each permit space. For example, methane is lighter than normal air and will tend to be near the top of the space, while hydrogen sulfide is heavier and will be found toward the bottom of the area. Carbon monoxide will be found near the middle of the confined space. The air should be monitored every four feet from top to bottom.
  • Information and training to workers: Employers must inform workers of the existence, location and danger of the permit-required confined space by posting danger signs or by another effective method. Workers who enter confined space need to be trained about the dangers they might face, procedures for safe entry and work, and protective gear.
  • Ventilation: Blowers can be used to provide oxygen or get rid of harmful gases. This process, known as purging, normally takes at least 10 to 15 minutes depending on the size of the confined space. Ventilation should be continuous where possible, because in many confined spaces the hazardous atmosphere will form again when the flow of air is stopped.
  • Entry permits: Before entering a confined space, a permit must be filled out that includes the location, date and length of the job, who may enter, hazards, safe conditions for entry, air testing results, rescue and emergency services to be used if necessary, and other information.
  • Who may enter a confined space: Workers who enter confined space, entrants, must be trained about hazards in confined spaces and have proper equipment to work safely.
  • The role of the attendant: The attendant is outside the confined space and is there to ensure the safety of their co-worker. An attendant is in constant communication with the person in the confined space and to make sure ventilation is working, monitor the air, and call for help.

Attendants can perform a rescue that does NOT require entry. They may only enter to perform a rescue if they are trained and another attendant is present outside the space. 

  • Rescue and emergency services: Retrieval systems such as tripods and winches are used to rescue workers without having to enter the space. Rescues that require entry may be done with either trained in-house staff or by an outside rescue service.
  • Personal protective equipment: In addition to using ventilation and other measures to get rid of hazards, workers need protective gear. This includes a full body or chest harness and may also require respirators, hard hats, goggles, earplugs or muffs, gloves, boots, or other protective clothing.

What laws apply to work in confined spaces?

The Occupational Safety and Health Administration (OSHA) has a standard to protect workers from the hazards of confined spaces. OSHA's Permit-required confined spaces standard, 29 CFR 1910.146, is available online.

For additional information, refer to the AFSCME Manual on Confined Spaces.

January 2001

For more information about protecting workers from workplace hazards, contact the AFSCME Health and Safety Program at 202-429-1215, or 1625 L Street, N.W., Washington, DC 20036.

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