Fact Sheet

Confined Space

A confined space is by design one with all or one of the following characteristics:

Types of Confined Spaces

Some have open tops and are very deep; others are enclosed spaces with limited (as small as 18”) openings for entry. The most hazardous type of confined space combines limited access and mechanical devices.

OSHA uses the term permit-required confined space (or permit space) to describe those spaces that both meet the definition of confined space and pose health or safety hazards. It is described under CFR 29 1910.146 Permit-required Confined Space.

Entry Reasons

Usually entry is to perform inspection, repair, maintenance (cleaning or painting), or similar infrequent or irregular activities. Entry may also be during new construction.


The hazards involved will be limited by the specific work practices. Constructing, or working in a confined space can result in bodily injury, illness and death to the employee. Dangers include explosion, poisoning and asphyxiation.

Hazardous Atmospheres

Because it is confined, the space has limited natural air movement. This can result in

Oxygen-Deficient atmospheres have less than 19.5% oxygen and should not be entered without approved self-contained breathing apparatus (SCBA). The type of work being done (welding, cutting or brazing) or certain chemical reactions (rusting) or bacterial action (fermentation) can reduce the oxygen level. Or oxygen can be replaced by a heavier gas (carbon dioxide or nitrogen).

Flammable atmospheres are caused by an oxygen-enriched atmosphere (above 21 percent), and a flammable gas, vapor or dust in the proper proportion. If sparking, electrical tool or other source of ignition is used in this scenario and explosion will occur.

Toxic atmospheres are created from toxic substances from the:

Product stored in the space can be absorbed into the walls and give off toxic gases when removed. Toxic gases can be given off when cleaning out residue of the stored product.

Work being performed (welding, cutting, brazing, painting, scraping, sanding, and degreasing) can create toxic atmospheres.

Work in areas adjacent to the confined space can create toxicants that can enter and build-up in the confined space.

General Physical Hazards

Temperature extremes—extremely hot or cold temperatures can cause harm to workers.

Engulfment—Grain, sand, coal or other loose, granular material stored in bins and hoppers can engulf and suffocate a worker. It can also form a crust or bridge in a bin and break loose under the weight of a worker.

Noise—amplifies in a confined space and damage the worker’s hearing and interfere with communications and shouted warnings.

Slick or Wet Surfaces—Slips and falls can cause injuries and deaths and increase the risk and results of electric shock from circuits, equipment and tools.

Falling Objects—are especially dangerous in confined spaces with topside openings or where work is being done above another worker.

Risk Management Strategies

Atmosphere Testing

Some gases and vapors are heavier than air (hydrogen sulfide) and sink to the bottom of confined spaces, others are lighter than air (methane) and rise to the top of the spaces, and others are same weight as air (carbon monoxide). Therefore, it is important to test top, middle and bottom of the confined space from the outside with a properly calibrated instrument to find out what gases are present. If oxygen deficiency or toxic gases or vapors are found, ventilate and retest before workers are allowed to enter. If ventilation is impossible and entry is necessary (emergency rescue) provide workers with appropriate respiratory protection.


A blower or fan is used to remove toxic gases and vapors from a confined space. The method and equipment used depend on the size of the entry, the gases to be exhausted and the source of air replacement air.


The confined space is removed from service by lockout (electrical sources), blanking and bleeding (pneumatic and hydraulic lines), disconnecting (belt and chain drives, and mechanical linkages on shaft-driven equipment where possible) and securing (mechanical moving parts with latches, chains, chocks and blocks).


Respirators are personal protective equipment that allows workers to safely breathe without inhaling toxic gases or particles. Air-purifying respirator filters dangerous substances from the air. Air-supplying respirators deliver a supply of safe air from a tank or an uncontaminated area nearby. Select the proper PPE for the job, the hazard and the person. Thoroughly train workers in the use and limitations of respirators before they are allowed to use them in a confined space situation.

Standby and Rescue

More than 50 percent of the workers who die in confined spaces are attempting to rescue others. Rescuers must be trained to follow established emergency procedures and use proper equipment and techniques. Rescues should be planned and drills should be run to get people familiar with emergency procedures.


Never use pure oxygen to ventilate a confined space that will cause flammable materials (clothing, hair) burn violently when ignited. Ventilate with normal air.

Only air-supplying respirators should be used in confined spaces where there is not enough oxygen.

Always test the air prior to anyone entering the confined space and take appropriate precautions.

Consider the interplay of hazards associated with a confined space, such as the risk of flammable vapors or gases, the build-up of static charge from mechanical cleaning (abrasive blasting), which all influence the precautions that must be taken to protect the health and safety of the employee.

Never trust your senses to determine if the air in a confined space is safe. Many toxic gases and vapors are invisible and odorless, and the percentage of oxygen cannot be determined by any of the five senses.

A person should be assigned to remain on standby outside of the confined space and remain in constant communication with the worker(s) inside. They should only enter the space after help arrives and only with the proper lifelines and respirators.

Accidents in confined spaces, like all others, are required by federal regulations to be reported only if medical attention or loss of time from work or death is involve. Some states and workers’ compensation carriers have slightly more stringent requirements, but none required reporting of near misses.


A Guide to Safety in Confined Spaces, [DHHS (NIOSH) Pub. No. 87-113], July 1987

Confined Space Pre-entry Check List, 1910.146 App D

Confined Spaces, NIOSH, Workplace Safety and Health Topics

Criteria for a Recommended Standard: Working in Confined Spaces, [DHHS (NIOSH) Pub. No. 80-106], December 1979

elaws—OSHA Confined Spaces Advisor The OSHA Confined Spaces Advisor provides guidance to help employers protect workers from the hazards of entry into permit-required confined spaces. The Advisor will help you determine if a space is covered by OSHA’s Permit-Required Confined Spaces regulation. The system provides options to review the definitions of technical terms, to review answers to frequently asked questions, and to review the regulatory text.

Examples of Permit-required Confined Space Programs, 1910.146 App C

OSH Answers: Confined Space-Introduction, Canadian Centre for Occupational Health and Safety

OSH Answers: Confined Space-Program, Canadian Centre for Occupational Health and Safety

The OSHA Confined Space Advisor 1.1

OSHA Expert Systems Software

Procedures for Atmospheric Testing, 1910.146 App B