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How Do I Know If I’m Entering a Confined Space?

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How do I know if I’m entering a space that’s considered “confined”? How do I know if it needs to comply with regulatory laws and requirements?

These are questions many employers deal with when their employees are doing work activities in or near enclosed areas or manholes, ventilation ducts, pits, tunnels, tanks, and areas with very little air movement.

The first concern for any employer is to determine whether the space or area meets the definition of a confined space as specified by the regulatory authority having jurisdiction at the worksite. If the area does comply with the definition of the regulatory standard, then the employer is required to follow the required written actions specified.

OSHA Definitions

In the United States, the main authority having jurisdiction in this area is the Occupational Safety and Health Administration (OSHA). The confined space standard from OSHA states:

For General Industry worksites:

Applicable regulation-1910.146, which is law in general industry for permit-required confined space entry, first requires that spaces meet the definition of confined space.

1910.146 definition of confined space.

1. Is large enough and so configured that an employee can bodily enter and perform assigned work; and

2. Has limited or restricted means for entry or exit (for example, tanks, vessels, silos, storage bins, hoppers, vaults, and pits are spaces that may have limited means of entry); and

3. Is not designed for continuous employee occupancy.

This is the definition in general industry for a confined space (CS). If the space meets that definition in a general industry workplace, then it is a confined space.

• For construction activity worksites: 1926.1202 definition of confined space.

1. Is large enough and so configured that an employee can bodily enter it; and

2. Has limited or restricted means for entry and exit; and

3. Is not designed for continuous employee occupancy.

OSHA does not require the employer to do any activity unless the space meets the definition of a permit space, which follows.

Permit-required confined space definitions are the same for general industry 1910.146 as it is for the confined spaces in construction standard 1926.1202, also referred to as a permit-required confined space, or PRCS, and states the following:

First, it must meet the definition of a confined space and have one or more of the following characteristics:

1. Contains or has a potential to contain a hazardous atmosphere;

2. Contains a material that has the potential for engulfing an entrant;

3. Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross-section; or

4. Contains any other recognized serious safety or health hazard.

If the space meets the definition of a permit space in general industry or construction, then the employer must follow the actions specified in the standard’s requirements for entering a PRCS, such as testing, filling out a permit, verifying rescue services are readily available and equipped if required, training of employees in hazards, and confined space entry procedures to ensure a safe entry.

If you read the standard’s requirements, they discuss alternate entry procedures with ways of entering if certain hazards are present or not present and how to enter and not have a rescue service standing by. But each standard is very specific in allowing entry without a permit, so you will need to read the exceptions to those rules of law.

ANSI Definitions

Consensus standards that are recommended if you want to comply with procedures that go beyond the minimum requirements of the law specified by OSHA are the following: American National Standards Institute (ANSI)/American Society of Safety Professionals (ASSP) Z117.1 Revised 2022 for General Industry and ANSI/ASSP A10.43 developed in 2016 for Construction sites.

ANSI/ASSP Z117.1 Confined Space definition includes:

Enclosed area large enough and configured to allow a person to bodily enter and has the following characteristics:

• Its primary function is other than human occupancy;

• Has restricted entry and exit. (Restricted entry and exit is a physical configuration, which requires the use of the hands for support or contortion of the body to enter into or exit from a confined space.)

ANSI/ASSP Z117.1 Revised 2022 states the following: This national consensus standard provides minimum safety requirements to be followed while entering and working in confined spaces at ambient atmospheric pressure. In the 2022 version of Z117.1, the committee reviewed data from OSHA’s fatality database (2019) to include federal and state cases involving workers that have died on the job.

From this data, cases involving confined spaces were extracted and only those involving asphyxiation and poisons such as possible atmospheric hazards (i.e., oxygen deficiency, carbon monoxide, hydrogen sulfide, etc.), and engulfments (i.e., grain, water), or falls and mechanical hazards were used.

Sorting through the data shows that asphyxiants and toxic atmospheres are still the leading cause of death in confined spaces (~57%), with engulfment in grain silos and storage bins a very close second (~43%).

Examples of confined spaces include, but are not limited to, tanks, silos, vessels, pits, sewers, pipelines, penstock, boilers, septic tanks, utility vaults, tank cars, and other mobile containers. Temporary structures also need to be evaluated to determine if they meet the definition of a CS.

A confined space is either classified as a non-permit confined space (NPCS) or a PRCS. Simply stated, a PRCS is a confined space that, after evaluation, is found to contain actual or potential serious hazards, and due to the severity of the hazards, requires written authorization (permit) for entry.

ANSI A10.43 – 2016 Confined Spaces in Construction and Demolitions Operations.

Defines a “Confined Space,” which is different than the ANSI general industry confined space definition, as a space that has all of the following characteristics:

1. Has limited or restricted means for entry and exit;

2. Is not designed for continuous employee occupancy; and

3. Is large enough and so arranged that an employee can bodily enter it.

Defines a “Permit Confined Space” as a confined space that has one or more of the following characteristics:

1. Contains or has the potential to contain a hazardous atmosphere that ventilation will not reduce to, and maintain at, a safe level;

2. Contains a material that has the potential for engulfing an entrant;

3. Has an entrapment hazard; or

4. Contains any other recognized hazard that has the potential of causing serious physical harm.

If the employer’s employees are about to enter a permit space as indicated in the previous definitions, then the employer is required to do some or all of the following:

1. Conduct atmospheric tests for oxygen percent by volume, lower explosive limit (LEL) in %LEL/lower flammable limit (LFL) for the gas or vapor present, toxics present, or potentially could be present because of the work activity, such as carbon monoxide, hydrogen sulfide, carbon dioxide, chlorine, solvents in paints and coating, pesticides, and inert gases from products used to prevent fruits and vegetables from ripening during storage or transport. If you do not have a calibrated 4 or 5 gas meter, they can be rented from instrument manufacturers.

2. Ensure a local rescue service is available if required. Some entries do not require a rescue service, such as entering under alternate procedures so review those requirements and see if you may qualify for entering a PRCS without a rescue service. Otherwise, the standards addressing entry into permit spaces require that a rescue service be available and equipped to perform an emergency evacuation if the occasion arises.

3. Arrange for effective decontamination procedures for cleaning equipment, clothing, and people that have entered the permit space so any contaminants are not taken to people’s transportation means or home. The employer needs to have a written emergency evacuation plan in place with adequate practice with members of the entry team.

ANSI/ASSP Z117.1 Revised 2022 contains a lot of information concerning the hazards of confined spaces. It will supply the reader with possible work practices, information on effective employee training, test instrument use and calibration, and much, much more.

Stay Safe

Know whether you or your team are entering a confined space. If you are, be prepared ahead of time with the use of standards such as these that are pertinent to your region.

Editor’s note: This article first appeared in the September 2023 print issue of CoatingsPro Magazine. Reprinted with permission.

About the Author:

Terry W. Krug, MS, CSP, CIH, is president and senior scientist for Exceptional Occupational Safety and Health Advisors, Inc. (EXOSHA). He was the main author of “Confined Space Entry: An AIHA Protocol Guide” from 1995 and co-author of the revised version from 2001. For more information, contact: Terry Krug, (630) 863-5359,

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