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permit required
General industry employers can use this flow chart to determine if spaces are permit spaces.
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Do Not Enter sign

Confined Space Basics

OSHA's Confined Space Standard

OSHA’s standard for confined spaces (29 CFR 1910.146) contains the requirements for practices and procedures to protect employees in the general industry from the hazards of entering permit spaces.

General industry employers must evaluate their workplaces to determine if spaces are permit spaces. If a workplace contains permit spaces, the employer must inform exposed employees of their existence, location and the hazards they pose.

This can be done by posting danger signs such as “DANGER-PERMIT-REQUIRED CONFINED SPACE-AUTHORIZED ENTRANTS ONLY” or using an equally effective means. If employees don’t need to enter and work in permit spaces, employers must take effective measures to prevent them from entering these spaces. An employer is required to block or securely seal off the confined space so employees cannot enter the area. If employees are expected to enter permit spaces, the employer must develop a written permit space program and make it available to employees or their representatives.

Confined Space Definition

OSHA’s definition of a confined space is a space that:

  • is large enough and configured so an employee can enter and perform assigned work;
  • has limited or restricted means for entry or exit;
  • and, is not designed for continuous employee occupancy.

Additionally, the ANSI standard defines a confined space as, “an enclosed area large enough and configured to allow a person to enter.”

According to ANSI, a confined space also has the following characteristics:

  • Its primary function is other than human occupancy.
  • It has restricted entry and exit. This means the entry and exit is a physical configuration, which requires the use of the hands for support to enter into or exit from a confined space.
A manhole is an example of a confined space.

Here are some examples of confined spaces:

  • Tanks
  • Manholes
  • Boilers
  • Furnaces
  • Sewers
  • Silos
  • Hoppers
  • Vaults
  • Pipes
  • Trenches
  • Tunnels
  • Ducts
  • Bins
  • Pits

Why Confined Spaces are Hazardous to Entrants


Confined spaces are deceiving. A confined space often appears to be harmless; no danger signs are apparent and the space may have been entered on prior occasions without incident. However, a worker cannot assume conditions have not changed and the space is safe for entry each time. Some materials may pose an immediate threat to the life and health of the worker entering the space. However, the dangerous materials, such as hydrogen fluoride gas, may cause a sudden or fatal collapse 12-72 hours after exposure. The victim “feels normal” after recovery from transient effects until collapse. Such materials in hazardous quantities are considered to be “immediately” dangerous to life or health.

Below is a list of other hazards that could be encountered while working in a confined space:

  • Space configurations such as small openings and inwardly converging walls, which can trap an entrant, restrict easy entry and exit, or impede rescue.
  • Atmospheric hazards such as gasoline tank vapors, combined with limited ventilation. Such conditions can cause asphyxiation or explosion.
  • Physical hazards, such as unstable grain contained in silos, which can engulf a worker.
  • All other serious hazards associated with general industry, such as electrical equipment, moving machinery, falling objects, and wet or slippery surfaces.

Below is a list of potential hazards to be aware of when working in a confined space:

  • No ventilation (pits and vaults seldom opened).
  • Leaking chlorine gas (which is heavier than air) can accumulate in low-lying spaces.
  • Oxygen depletion; which can be caused by:
    • Rotting vegetation and decaying dead animals.
    • Corroding or rusting machinery.

Real-Life Accident

A 49-year-old worker suffocated inside of a chemical tank at the Port of New Orleans. The Occupational Safety and Health Administration (OSHA) said the Illinois company, Dedicated Tank Cleaning Services, sent Armond Stack and two others into a tank in October 2015 without first testing the air quality of providing them lifelines. As a result, Stack was killed and the others were hospitalized.


OSHA is proposing $226,000 in fines against the company in connection with nine safety violations. Two of the nine proposed violations were classified as “willful,” which is the most serious category. This category is reserved for situations where an employer knows of an unsafe condition or practice, but does nothing about it.

Before Stack’s death, OSHA cited the company for almost 30 violations. Many of those violations were related to failure to take proper precautions when sending workers into confined spaces filled with dangerous chemicals.

Glossary of Terms

Take a look at a glossary of terms for confined spaces, according to 29.CFR 1910.146:

Acceptable Entry Conditions: The conditions that must exist in a permit space to allow entry and to make sure employees involved with a permit-required confined space entry can safely enter into and work within the space.

Attendant: An individual stationed outside one or more permit spaces who monitors the authorized entrants and who performs all attendant duties assigned in the employer’s permit space program.

Authorized Entrant: An employee who is authorized by the employer to enter a permit space.

Blanking or Blinding: The absolute closure of a pipe, line or duct by the fastening of a solid plate that completely covers the bore and is capable of withstanding the maximum pressure of the pipe, line or duct with no leakage beyond the plate.

Double Block and Bleed: The closure of a line, duct or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves.

Emergency: Any occurrence (including any failure of hazard control or monitoring equipment) or event internal or external to the permit space that could endanger entrants.

Glossary of Terms (Continued)

Engulfment: The surrounding and effective capture of a person by a liquid or finely divided solid substance that can be aspirated to cause death by filling or plugging the respiratory system or that can exert enough force on the body to cause death by strangulation, constricting or crushing.

Entry: The action by which a person passes through an opening into a permit-required confined space. Entry includes ensuring work activities in that space and is considered to have occurred as soon as any part of the entrant’s body breaks the plane of an opening into the space.

Entry Permit: The written or printed document that is provided by the employer to allow and control entry into a permit space.

Entry Supervisor: The person (such as the employer, foreman or crew chief) responsible for determining if acceptable entry conditions are present at a permit space where entry is planned.

Hazardous Atmosphere: An atmosphere that may expose employees to the risk of death, incapacitation, and an impairment of ability to self-rescue, injury or acute illness from one or more of the following causes:

  • Flammable gas, vapor or mist in excess of 10 percent of its lower flammable limit. (LFL);
  • airborne combustible dust at a concentration that meets or exceeds its LFL;
  • atmospheric oxygen concentration below 19.5 percent or above 23.5 percent;
  • and, any other atmospheric condition that is immediately dangerous to life or health.

Glossary of Terms (Continued)

Hot Work Permit: The employer’s written authorization to perform operators capable of providing a source of ignition.

Immediately Dangerous to Life or Health (IDLH): Any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that would interfere with an individual’s ability to escape unaided from a permit space.

Inerting: The displacement of the atmosphere in a permit space by a non-combustible gas to such an extent that the resulting atmosphere is non-combustible. (NOTE: This procedure produces an IDLH oxygen-deficient atmosphere.)

Isolation: The process by which a permit space is removed from service and completely protected against the release of energy and material into the space by such means as: blanking or blinding; misaligning or removing sections of lines, pipe, or ducts; a double block and bleed system; lockout or tagout of all sources of energy; or blocking or disconnecting all mechanical linkages.

Oxygen Deficient Atmosphere: An atmosphere containing less than 19.5% oxygen by volume.

Oxygen Enriched Atmosphere: An atmosphere containing more than 23.5% oxygen by volume.

Permit-required Confined Space Program/Permit System: Employer’s overall program for controlling and protecting employees from permit space hazards and for regulating employee entry into permit spaces. Employer must have a written procedure for preparing and issuing permits.

Glossary of Terms (Continued)

Prohibited Condition: Any condition in a permit space that is not allowed by the permit during the period when entry is authorized. (Example: hot work)

Rescue Service: The personnel designated to rescue employees from permit spaces.

Retrieval Service: The equipment (including a retrieval line, chest or full-body harness, wristlets, if appropriate and a lifting device or anchor) used for non-entry rescue of persons from permit spaces.

Testing: The process by which the hazards that may confront entrants of a permit space are identified and evaluated. Testing includes specifying the tests that are to be performed in the permit space.

Permit-Required Confined Space

A permit-required confined space is space that has one or more of the following characteristics:

  • Contains or has potential to contain hazardous atmosphere
  • Contains material that has the potential for engulfing entrant
  • Has internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by floors or slopes downward and tapers to smaller cross-section
  • Contains any other serious safety or health hazard

Some examples of permit-required confined spaces are manholes going into sewers, grain silos and trenches.

Real-Life Scenario

On February 4, 2004, a 23-year-old tank mechanic died when he entered a permit-required confined space. The mechanic was assigned to prepare a shipping container used to transport silicon tetrachloride for an inspection. The tank had been purged with an inert nitrogen atmosphere. While waiting for the inspector to arrive, the mechanic entered the tank for an unknown reason, apparently without first testing the atmosphere, and died of asphyxiation. When the victim was discovered about an hour later, a coworker jumped into the tank. He also didn’t test the atmosphere first and lifted the victim up to others standing on top of the tank. Testing by fire department responders showed the atmosphere at the bottom of the tank to be about 12% oxygen, below the minimum safe level of 19.5% oxygen.



  • Employers must evaluate confined spaces in the workplace. A permit-required confined space requires written entry procedures, including posted documentation of test results by an authorized person.
  • Never enter a confined space without first testing the atmosphere with an appropriate air-monitoring instrument.
  • Never enter a confined space without appropriate personal protective equipment for safe entry.

A trained attendant must monitor workers in a confined space and be prepared for an emergency response that does not involve a direct entry of the space.

Non-Permit Required Confined Space

This is a confined space that does NOT contain or have the potential to contain any hazard capable of causing death or serious physical harm.

Here are some examples of a non-permit required confined space:

  • Drop ceiling
  • Motor control cabinets

Location of Confined Spaces

Confined spaces are found not only in industrial settings but also in public places such as shopping malls and large public swimming pools. Waterfalls and water fountain displays used in malls for beautification may have pump vaults or valve pits that are seldom entered. Some swimming pool pumps are placed in vaults below ground. There have been reports of maintenance employees entering these areas and losing consciousness.

That was a lot of information to remember! It’s now time for the first module quiz. Good luck!



Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. What must an employer do if workers need to enter permit confined spaces?

2. Which of the following are examples of a confined space?

3. Dangerous materials in a confined space may cause a sudden or fatal collapse _____ after exposure.

4. _____ is a condition that poses an immediate or delayed threat to life.

5. A(n) _____ is an atmosphere containing less than 19.5% oxygen by volume.

Have a great day!

Important! You will receive an "error" message unless all questions are answered.