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Confined Space Safety Basics



In order to fully understand the information offered in this course, you must first understand the terms used. So, let's take a look at some important definitions for common confined space terms used by most industries and regulatory agencies.

What is a confined space?

That depends on where you're working. In the United States, a confined space is defined by OSHA as a space that meets the following three criteria:

  1. The space is large enough and configured such that an employee can bodily enter and perform work;
  2. The space has limited means of entry (access) and exit (egress), which means you need to use your hands or contort your body to enter the space; and
  3. The space is not designed for continuous employee occupancy.

In Canada, each province may have their own definition of a "confined space," and each of these definitions may be slightly different from OSHA's definition in the U.S. Generally, regulatory agencies in Canada define a confine as having the following three characteristics:

  1. It is a fully or partially enclosed space;
  2. It is neither designed nor constructed for continuous human occupancy; and
  3. It is a space in which atmospheric hazards may occur because of its construction, location or contents or because of work that is done in it.
There are several different types of confined spaces
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Definition Differences

  • In the United States, a confined space must be large enough for bodily entry. In Canada, the size of the space doesn't matter. Therefore, we may assume it must be large enough for part of the body, like the head, to enter. Actually workers have been killed in confined space only after sticking their heads through a hatch or lid. Workers have also been killed in rather shallow trenches. To have a fatal confined space accident, all it takes is a trench or ditch a couple of feet (or a meter) in depth, and a heavier-than-air hazardous atmosphere.
  • To be considered a confined space in the United States, the space must have limited access or egress. There is no such requirement in Canada. Examples of limited access are hatches or covers.
  • In both the U.S. and Canada, a confined space must not be designed for human/employee occupancy.
  • And finally, in Canada the space must have the potential for developing a hazardous atmosphere. In the United States, this requirement is not included in the definition.

In this course, we will focus on confined space entry as defined by OSHA in the USA.

Reasons for Entering Confined Spaces

Entering a confined space may be done for various reasons. It is done usually to perform a necessary function, such as inspection, repair, maintenance (cleaning or painting), or similar operations which would be an infrequent or irregular function of the total industrial activity.

Entry may also be made during new construction. One of the most difficult confined space entries to control is that of unauthorized entry, especially when there are large numbers of workers and trades involved, such as welders, painters, electricians, and safety monitors.

A final and most important reason for entry would be emergency rescue. This, and all other reasons for entry, must be well planned before initial entry is made and the hazards must be thoroughly reviewed.

Permit-Required Confined Spaces (PRCS)

By definition, a permit-required confined space is a space that meets the criteria for a confined space and has one or more of the following characteristics:

  1. It contains or has the potential to contain a hazardous atmosphere;
  2. It contains a material with the potential to engulf someone who enters the space;
  3. It has an internal configuration that might cause an entrant to be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross section; or
  4. It contains any other recognized serious safety or health hazards.

See the Confined Space Entry Decision Flow Chart by clicking the appropriate tab at the top of this page to help you determine if your confined spaces need a permit.

Are these confined spaces?
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Examples of Confined Spaces that Could Become Permit Spaces

Most confined spaces are designed to hold substances such as liquids, gases, and loose materials, or to house equipment. They come in many sizes and shapes, though most can be classified in one of two ways: those with depth and open tops and those with narrow openings. Below are examples of each.

  • Open-topped spaces and deep spaces with narrow openings
  • Pits
  • Ship compartments
  • Wells
  • Silos
  • Vats
  • Pipes
  • Hoppers
  • Tunnels
    • Bins
    • Tanks
    • Degreasers
    • Casings
    • Kettles
    • Sewers

    Check out this short audio clip by Dan Clark of the that defines and discusses the characteristics of permit-required confined spaces.

    Where Confined Spaces are Found


    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.

    Take a look at this discussion that includes examples of where confined spaces are found in construction.

    The general industry confined space standard does not address the unique characteristics of confined spaces in construction, therefore OSHA is creating a separate rule to protect employees from the hazards resulting from exposure to confined spaces in the construction industry.

    Read more about the standard from our partner, HSE Press.

    Why Confined Spaces are Hazardous to Entrants

    Confined space hazards are usually present.
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    By their very nature, confined spaces can be hazardous. Below is a list of hazards:

    • 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:

    • 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.

    Read these actual confined space accident summaries to learn more about the dangers of confined spaces.

    What is Confined Space "Entry"?

    Confined space entry.
    (Click to enlarge)

    A confined space entry is considered to have occurred when any part of a person's body crosses the plane of an opening into the space. Each employer should ask these two questions at the onset of each project:

    1. Is confined space entry always necessary for this task?
    2. Is it possible to complete the task from the outside?

    If possible, avoid entering a confined space. Every consideration should be given to completing the task from the outside.

    Using Alternative Entry Procedures

    Under certain conditions, you may use alternate procedures for worker entry into a permit space. For example, if you can demonstrate with monitoring and inspection data that the only hazard is an actual or potential hazardous atmosphere that can be made safe for entry using continuous forced air ventilation, you may be exempted from some entry requirements, such as permits and attendants.

    However, even in these circumstances, you must test the internal atmosphere of the space for oxygen content, flammable gases and vapors, and the potential for toxic air contaminants before any employee enters it. You must also provide continuous ventilation and verify that the required measurements are performed before entry.

    Flow Chart

    Sample Flow Chart
    (Click to enlarge)

    Confined Space Entry


    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. Which of the following is not one of the three OSHA-defined criteria of a confined space?

    2. One of the most difficult confined space entries to control is that of _____ entry.

    3. Which of the following is one of the four characteristics of a permit-required confined space?

    4. A confined space entry is considered to have occurred when any part of a person's body crosses the plane of an opening into the space.

    5. When using alternative confined space entry procedures, you must test the _____ of the space.

    Have a great day!

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