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Course 816 - Confined Space Safety in Construction

Safety guides and audits to make your job as a safety professional easier

Construction Confined Space Basics

confined space
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What is a Confined Space?

Before we get into the requirements of a confined space program, let's discuss the basic characteristics of a confined space. In the United States, a confined space is a space that meets each of the following three conditions:

  1. It is large enough and so configured that an employee can fully enter the space and perform work.

A space that is just large enough for a person to squeeze into, but not perform any work, is not a confined space. Similarly, a space that is too small for a person to enter completely is not a confined space. Note: In Canada, according to the Canadian Centre for Occupational Health and Safety (CCOHS), the size of the space does not matter. A confined space is an enclosed or partially enclosed space that:

  • Is not primarily designed or intended for human occupancy
  • has a restricted entrance or exit by way of location, size or means
  • can represent a risk for the for the health and safety of anyone who enters
  1. It has limited or restricted means for entry, exit, or both.

If a person must contort his or her body to enter or move around inside a space, it probably has a limited means of entry and exit. Climbing through a porthole or hatch to enter a space or crawling through a tunnel toward an exit are examples of spaces that have limited means of entry and exit.

Another way of measuring limited means of entry and exit is to determine how difficult it would be to remove an injured person from the space. If there is a need for a technical rescue to remove an injured person, you probably have a limited means entry and exit. Evaluate each space on a case-by-case basis.

  1. It is not designed for continuous human occupancy.

What is the primary function and purpose of the space? A space that is designed for periodic occupancy is not the same as a space that is designed for continuous occupancy.

The presence of a fixed ladder, lighting, or ventilation does not always mean the space was designed for continuous occupancy. Is the space designed for a person to work there or is it designed to house and protect equipment that needs to be monitored or occasionally maintained? For example, a space may have lighting for periodic occupancy that may be necessary to safely enter and exit, read gauges, or perform maintenance or repairs.

Ventilation may be necessary to keep equipment from overheating or to provide fresh air for temporary job assignments or tasks. In both cases, the work performed is intermittent or temporary.

What is a Permit Space?

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A permit space is a confined space that also has one or more of the following characteristics:

  • It has — or could have — a hazardous atmosphere.
  • It contains material that could trap or bury a person.
  • It is shaped so that a person could become trapped or asphyxiated.
  • It has other safety or health hazards that could harm a person.

Most accidents in permit spaces happen when workers and untrained rescuers do not recognize hazards in the spaces or they do not control the hazards before they enter. Never assume a permit space is safe to enter. Permit spaces can have two types of hazards: hazardous atmospheres and physical hazards.

To help identify the spaces on a worksite, see this sample checklist.

Hazardous Atmospheres

Confined Spaces: Deadly Spaces
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A hazardous atmosphere affects the air in the space and can cause death or acute illness, or impair the ability of workers to escape. Hazardous atmospheres include:

  • Corrosive atmospheres: Corrosive atmospheres accumulate from some manufacturing processes and biological or chemical reactions. Some cause immediate damage to the skin and eyes; some have no immediate effect, but cause cancer with prolonged exposure.
  • Flammable or explosive gasses, liquids, vapors, mists, fibers, or dusts: Flammable gases such as acetylene, butane, propane, hydrogen, and methane are common in permit spaces. Grain, nitrated fertilizers, and ground chemicals can produce combustible dusts.
  • Air or oxygen displacement: Some substances (such as inerting gasses) can displace air or oxygen in a confined space; examples include nitrogen, helium, steam, Freon, argon, and carbon dioxide.
  • Oxygen deficiency: Oxygen-deficient atmospheres (oxygen concentration below 19.5 percent) affect heart rate, muscle coordination, and breathing. Unprotected workers cannot survive in an oxygen-deficient atmosphere.
  • oxygen deficiency
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  • Oxygen enrichment: Oxygen-enriched atmospheres (oxygen concentration above 23.5 percent), which can be caused by welding and from the improper use of oxygen for breathing air, increase the risk of fire or explosions.
  • Toxic dusts, mists, fumes, smoke, vapors, fibers, or gases: These can be released by manufacturing processes, stored materials, and work tasks. A hazardous atmosphere that poses a threat to life, would cause irreversible adverse health effects, or that would interfere with an individual's ability to escape from a confined space is called immediately dangerous to life or health (IDLH).

Some hazardous atmospheres (hydrogen fluoride gas and cadmium vapor, for example) may cause serious health effects that result 12 to 72 hours after exposure.

Air-monitoring Equipment

Trained employees can use an air-monitoring meter to test for hazardous atmospheres.

Trained employees can use an air-monitoring meter to test for hazardous atmospheres. However, they must first calibrate the meter and use it according to the manufacturer's instructions.

Inaccurate instruments can expose workers to excessive levels of toxic gas or an oxygen-deficient atmosphere. The only way to guarantee that an instrument will detect gas accurately is to test it every day before you use it using a “bump test.”

A bump test verifies that an air-monitoring meter is properly calibrated. You perform a bump test by exposing the meter to a known concentration of test gas. Compare the instrument reading to the actual quantity of gas present. If the instrument's response is within an acceptable tolerance range of the actual concentration, then the meter is calibrated properly.

physical hazards
Physical hazards come in many different forms.

Physical Hazards

Physical hazards come in many different forms and can cause death or serious physical harm. Examples include:

  • Access problems: In an emergency, entrants may not be able to exit quickly.
  • Absorbed chemicals: Chemicals can be absorbed through the skin or other tissues or membranes such as the eyes.
  • Corrosive chemicals: Corrosive chemicals can cause severe eye or skin damage if exposed workers are not wearing protective clothing or eyewear.
  • Falling objects: Objects can fall into the space because topside openings are unguarded or improperly guarded.
  • This is an excellent short video produced by WorkSafeBC.
    Click to play video
  • Illumination problems: Poor lighting makes it difficult for workers to enter, work in, and exit a permit space.
  • Inwardly converging surfaces: Inwardly converging walls and downward sloping floors that taper to a smaller cross section can trap a worker.
  • Material that could trap or bury a person: Loose materials drawn from the bottom of storage bins can suffocate or bury a worker. Liquids or materials that are suddenly released into the space can have the same effect.
  • Mechanical, electrical, hydraulic, and pneumatic energy: Mechanical and hydraulic equipment can move unexpectedly. Workers servicing mechanical and hydraulic equipment can be seriously injured or killed if the energy is not properly controlled.
  • Noise: Noise interferes with essential communication between workers in a confined space and those who are monitoring their work on the outside. High noise levels can impair hearing and cause hearing loss. Permit spaces can amplify sounds produced by tools and equipment.
  • Radiation: Sources of radiation include x-rays, isotopes, lasers, and welders.
  • Slippery surfaces: Wet, slippery surfaces increase the risk of falls. Leaks, spills, and condensation are common in permit spaces.
  • Extreme temperatures: Hot environments put workers at risk for heat stress, especially when they do strenuous work or are wearing protective clothing. Cold environments make their tasks more difficult to accomplish.

Eliminating Physical Hazards

physical hazards
A worker checks to make sure a pipe is blanked.

Ways to eliminate physical hazards in a confined space include:

Always evaluate the space in its normal state before eliminating hazards.

Identifying Confined Spaces

confined spaces
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When identifying confined spaces on a worksite, the employer should assume any confined space is a permit space, unless you determine the space to be a non-permit confined space. Before work begins at a worksite, each employer must:

  • ensure a competent person identifies all confined spaces in which one or more of the employees it directs may work, and
  • identify each space that is a permit space, through consideration and evaluation of the elements of that space, including testing as necessary.

A “Competent Person” is one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has the authorization to take prompt corrective measures to eliminate them.

Examples of Confined Spaces in Construction

Examples of locations where confined spaces may occur include, but are not limited to, the following:

Bins Air Receivers Vessels Drilled Shafts
Boilers Transformers Cesspools Digesters
Manholes Bag Houses Sludge Gates Silos
Scrubbers Pits Turbines Storm Drains
Vaults Tanks Mixers/Reactors Chillers
Water Mains Crawl Spaces Incinerators Attics
Blades (wind) Ducts Sewers Lift Stations

Confined Space in Crawl Spaces and Attics

crawl spaces
Crawl spaces can present many confined space hazards.

Crawl spaces and attics can be both confined spaces and permit spaces under the new standard. For instance, working in an attic and applying a large amount of spray foam (or another chemical) in a short period of time can expose a worker to low oxygen levels or a hazardous atmosphere.

In addition, changes to the entry/exit, the ease of exit, and air flow could create a confined space or cause the space to become permit space.

Crawl spaces can present many confined space hazards, including:

  • atmospheric hazards (e.g., flammable vapors, low oxygen levels)
  • electrocution (e.g., using electrical equipment in wet conditions, unprotected energized wires)
  • standing water
  • poor lighting
  • structural collapse
  • asbestos insulation

Working in attics can also present confined space hazards, such as:

  • atmospheric hazards (e.g., poor ventilation)
  • heat stress
  • mechanical hazards (e.g., attic ventilators, whole house fans)
  • electrical hazards (e.g., damaged or frayed wires, open electrical boxes)
  • slip, trip and fall hazards
  • asbestos insulation

Confined Spaces in Sewer Systems

Sewer systems can present a host of common confined space hazards.

Confined space hazards in sewer systems have led to worker deaths. Types of sewer systems include sanitary (domestic sewage), storm (runoff), and combined (domestic sewage and runoff). Sewer systems are extensive and include many different components that are considered confined spaces, including pipelines, manholes, wet wells, dry well vaults, and lift/pump stations. Therefore, employers conducting work in sewer systems will likely have workers who will encounter confined spaces.

Sewer systems can present a host of common confined space hazards, including:

  • atmospheric hazards (low oxygen, toxic or flammable gases)
  • chemicals in piping and from roadway runoff (may harm lungs, skin, or eyes)
  • engulfment and drowning
  • electrocution (e.g., using electrical equipment in wet working conditions)
  • slips, trips, and falls
  • falling objects
  • high noise levels, low visibility, limits to communication, and long distances to exits

Construction work can create confined spaces and permit spaces, even if there are none at the start of a project. Changes to the entry/exit, the ease of exit, and air flow could produce a confined space or cause one to become permit space.

Employer Actions

employer actions
Inform exposed employees by posting danger signs.

The employer who identifies or receives notice of one or more permit spaces on a worksite must:

  • Post danger signs. Inform exposed employees by posting danger signs warning of the existence and location of, and the danger posed by, each permit space. The employer may use any other equally effective means to inform exposed employees. A sign reading “DANGER -- PERMIT- REQUIRED CONFINED SPACE, DO NOT ENTER” or using other similar language can be used.
  • Inform employees and contractors. Inform its employees' authorized representatives and the controlling contractor of the existence and location of, and the danger posed by, each permit space. The Controlling Contractor is the employer that has overall responsibility for construction at the worksite. Notice must be given in a timely manner and in a manner other than posting.
  • Prevent unauthorized entry. Take effective measures to prevent any unauthorized employees from entering permit spaces.
  • Develop a Permit Space Program. Develop and implement a written permit space program if any of its employees are directed and authorized to enter permit spaces. The written program must be available prior to and during entry for inspection by employees and their authorized representatives.

Check out this short audio clip byDan Clark of the that introduces you to the new construction confined space employer requirements.


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. In the United States, which of the following is one of the criteria for a confined space?

2. Which of the following is NOT one of the four criteria for a permit space?

3. Which of the following might reclassify a crawl space as a permit space?

4. Sewer systems can present a host of common confined space hazards, including:

5. When an employer identifies or receives notice of one or more permit spaces on a worksite the employer must _____.

Have a great day!

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