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4. Confined Spaces | Confined Spaces Guideline

Disclaimer: This resource has been prepared to help the workplace parties understand some of their obligations under the Occupational Health and Safety Act (OHSA) and regulations. It is not legal advice. It is not intended to replace the OHSA or the regulations. FOR FURTHER INFORMATION PLEASE SEE FULL DISCLAIMER

“confined space” means a fully or partially enclosed space,

  1. (a)  that is not both designed and constructed for continuous human occupancy, and
  2. (b)  in which atmospheric hazards may occur because of its construction, location or contents or because of work that is done in it.

If you have a space that is fully or partially enclosed, the two conditions – (a) and (b) above – must both apply before the space can be considered a "confined space".

Do I have a confined space in my workplace?

To determine whether a "space" meets the definition of a confined space consider the following 3 questions:

  • Is the space fully or partially enclosed?
  • Is the space not both designed and constructed for continuous human occupancy?
  • Might an atmospheric hazard occur?

The only way to determine if a "space" meets the definition for a "confined space" is to evaluate it. How the evaluation is done is up to the employer.

If you have a fully or partially enclosed space:

Is it designed and constructed for continuous human occupancy? Might an atmospheric hazard occur? Is it a confined space?
Yes Yes No
Yes No No
No Yes Yes
No No No

We have determined a specific space not to be a confined space as per the Confined Spaces Regulation, but still prefer to conduct some air sampling prior to entering just to ensure that nothing unforeseen has occurred. Does this mean that we have to implement a confined space program for this space?

No, assuming this space was properly evaluated ahead of time and deemed not to be a confined space as per the definition. However, there is nothing preventing employers from taking any additional precautionary measures for any other spaces outside of this regulation, including air sampling as an example. Even though confined space provisions do not apply, employers would still need to comply with other relevant regulatory requirements, where applicable.

Is there a difference between a "restricted space" and a "confined space"?

Yes. Only the Regulation for Health Care and Residential Facilities (O. Reg. 67/93) speaks of a "restricted space" in section 42. In this regulation a restricted space refers, in part, to a "space from which the egress of a worker is restricted, limited, or impeded". A “restricted space” may also be a confined space, thus, an evaluation of the space may determine that the area is either a confined space, a restricted space, or both.

Does the Confined Spaces Regulation apply to spaces that cannot be entered due to their size?

The Confined Spaces Regulation is intended to protect a worker who performs work within a fully or partially enclosed space that is not both designed and constructed for continuous human occupancy and in which atmospheric hazards may occur.

A confined space is a space that can be occupied by a person. It is the Ministry’s position that the opening of the confined space would, therefore, need to be of such a size that a person’s body could pass through it into the space. An entry is an action that is considered to have occurred as soon as any part of the entrant’s body breaks the plane of an opening into such a space, regardless of whether the intended work activities may or may not require whole body entry, such as atmospheric testing. Under such a condition, the Confined Spaces Regulation would apply.

If there is a space that has an opening of a size that a person’s body could not pass through it, the Confined Spaces Regulation would not apply even if a body part of a person (e.g. hands) would break the plane of such an opening to perform work activities. However, in these circumstances, the employer must still comply with other requirements under the OHSA, including taking every precaution reasonable in the circumstances for the protection of the health and safety of the worker. For example, there may be hazards associated with the space, such as explosive gases, and employers would need to comply with relevant regulatory requirements, where applicable, and take every precaution reasonable in the circumstances to protect workers working on or near these spaces.

Human Occupancy

To determine if a space is designed and constructed for human occupancy, one must look at the intent and construction of the space - what is the purpose of the space, or in other words, what was it intended for, and to what standards has it been designed and constructed to allow people to occupy it?

Although the regulation does not define human occupancy, the MOL uses the term ‘continuous human occupancy’ to refer to a space that has been designed and constructed in accordance with recognized codes and standards that contain provisions to make the space suitable for humans to occupy, such as provisions for structural adequacy, entry and exit, ventilation and lighting such that a human could continually occupy that space. Examples are the Ontario Building Code, the Ontario Fire Code, and CSA B52 (Mechanical Refrigeration Code).

Workspaces such as offices, arenas, maintenance rooms, control rooms, etc., are obvious places that are designed for humans to occupy for long periods of time (continuously). These spaces are not considered a confined space, regardless of the atmospheric hazards that may occur in them. However, occupational health and safety legislation and regulations apply and must be complied with to protect workers.

Other spaces, such as parts of a tunnelling operation or an underground mine (stopes, drifts, ramps, shafts, raises), are designed and constructed specifically for people to carry out work within them. Specific codes and standards and requirements are intended to make the space adequate for the health and safety of workers. However, parts of a tunnel or mine could be confined spaces. Tunnels and mines could also include confined spaces within them, such as bins, tanks, clean or dirty water sumps, and water storage dams.

Some examples of spaces that would not be considered as "both designed and constructed for continuous human occupancy" are:

  • storage tanks, tank cars, process vessels, boilers, pressure vessels, vats, bins, silos, bag-houses and other tank like compartments usually having only a manhole for entry
  • open topped spaces such as pump wells, augured caissons, pits or degreasers
  • pipes, sewers, ducts and similar structures
  • cargo tanks, cellular double bottom tanks, duct keels, ballast and oil tanks and void spaces
  • chutes, mill holes, ore bins, inside of a skip hanging in a shaft, crusher jaws
  • flues, chimneys, ovens or furnaces.

Structures such as vessels, sewers and tank cars are designed and constructed to play a role in part of a process. Their primary purpose is to contain, transport, move or manipulate materials or equipment and they are not primarily designed for people to occupy them. They may have structures such as ladders or platforms where workers can perform work within the space on occasion. However, these spaces were not designed for continuous human occupancy.

A construction project space that is intended for human occupancy but not yet completed in its construction is not considered a confined space if its stage of construction is suitable for continuous human occupancy. Some construction spaces such as sumps and tanks and projects within these spaces may be confined spaces, but not projects in general.

A chamber or vault may have cooling ventilation for equipment purposes and have a temporary access space, designed to allow workers to access pipes and equipment (perhaps by using ladders or a door). However, this does not mean that it has been designed to meet codes and standards that would allow workers to safely perform their duties on a regular basis within the chamber or vault. Therefore, these spaces are considered NOT to be both designed and constructed for continuous human occupancy.

What are examples of spaces that are both designed and constructed for continuous human occupancy?

Some examples include offices, service rooms (such as mechanical rooms, elevator rooms), shops, walk-in freezers and refrigerators, laboratories, flammable liquid storage and dispensing rooms, and rooms equipped with approved fire suppression systems.

Trenches that are under construction and that are in compliance with the O. Reg. 213/91 (Construction Projects) requirements (which cover access and egress, stability of the trench walls and adequate ventilation in the trench) would have been designed for continuous human occupancy during the construction phase – (by virtue of complying with O. Reg. 213/91).

What if I cannot determine if a space is not designed and constructed for human occupancy?

Where it is not obvious and your evaluation does not determine whether a workspace is or is not designed for continuous human occupancy, consider whether or not there may be an atmospheric hazard present because of its design, construction or location and the work to be performed.

If it is determined that no atmospheric hazard may occur, then the confined space provisions would not apply in any case, and the human occupancy question need not be considered.

Where an atmospheric hazard may exist and you are still uncertain as to whether the space is designed for human occupancy, you may wish to comply with the confined space provisions.

What if the space is so small, such as a six inch pipe?

Refer to answer in Section 4, Confined Spaces - “Does this regulation apply to spaces that cannot be entered due to their size?

Atmospheric Hazards

"atmospheric hazards" means,

  • (a)  the accumulation of flammable, combustible or explosive agents,
  • (b)  an oxygen content in the atmosphere that is less than 19.5 per cent or more than 23 per cent by volume, or
  • (c)  the accumulation of atmospheric contaminants, including gases, vapours, fumes, dusts or mists, that could,
    1. (i)  result in acute health effects that pose an immediate threat to life, or
    2. (ii)  interfere with a person's ability to escape unaided from a confined space.

In the definition of a confined space, what is meant by "in which atmospheric hazards may occur"?

The intent of this wording is to ensure that consideration is given to atmospheric hazards that may exist in the space or that may occur due to the following:

  • The construction of the space
  • The location of the space
  • The contents of the space
  • The work being done in the space.

The evaluation of the space to determine if the regulatory requirements apply may include consideration of previous data (including air sampling), knowledge of the process and space, data on space configuration (size, design, areas for pocketing, double wall, etc.) and knowledge and data on the generation and accumulation of contaminants. Historical information, such as previous incidents that occurred in the specific space or similar spaces, or incidents that have occurred with similar processes, should also be taken into account.

In determining whether a hazardous atmosphere may occur, consideration should, among other things, be given to the atmosphere that may be present or which is created by routine, normal work activities. While the potential consequences of unexpected events (such as the inadvertent cutting of a hose) need to be considered by the employer in order to take reasonable precautions, the risk assessment undertaken by the employer should determine whether these events would be within the scope of normal work activities.

What are possible sources of atmospheric hazards?

Sources of atmospheric hazards may include:

  1. Previous contents of the space. An example would be a tank with a residual amount of organic solvent in it, such as perchloroethylene.
  2. Atmospheric hazards generated from chemical reactions of materials present in the space. An example would be the decomposition of organic materials that would cause the formation of methane, a flammable gas, and hydrogen sulphide, a toxic atmospheric contaminant. Another example would be rusting, or oxidation, within a confined space that would consume oxygen and cause an oxygen deficiency.
  3. Activities performed in or about the space. Examples include welding, which generates welding fumes, and solvent cleaning, which generates solvent vapours.
  4. Hazardous contaminants that may inadvertently enter into the space from adjacent processes or locations. An example would be carbon monoxide from vehicle exhaust entering street manholes or a trench.

What is a "flammable gas"?

A "flammable gas" is a gas that is capable of being ignited and burned when mixed with the proper proportions of air, oxygen or other oxidizer.

Note: A "flammable gas" is defined by the National Fire Protection Association (NFPA) as a gas at 68°F (20°C) or less at an absolute pressure of 14.7 psia (101.325 kPa), that is ignitable at an absolute pressure of 14.7 psia (101.325 kPa) when in a mixture of 13 percent or less by volume with air, or that has a flammable range at an absolute pressure of 14.7 psia (101.325 kPa) with air of at least 12 percent, regardless of the lower limit.

What is a "flammable vapour"?

A "flammable vapour" is the vapour generated by a flammable liquid that is capable of being ignited and burned when mixed with the proper proportions of air, oxygen, or other oxidizer.

What is a "flammable liquid"?

A "flammable liquid" means a liquid with a flash point below 37.8 degrees Celsius and a vapour pressure not exceeding 275 kilopascals absolute at 37.8 degrees Celsius.

What is meant by "atmospheric contaminants, including gases, vapours, fumes, dusts or mists that could result in acute health effects that pose an immediate threat to life or interfere with a person's ability to escape unaided from a confined space"?

This refers to toxic airborne agents that when inhaled in high concentrations could cause acute health effects shortly after an overexposure. Acute health effects may include very serious outcomes such as impairment of judgement, unconsciousness, and death. Acute health effects such as irritation, narcosis or anaesthesia could also interfere with a person's ability to escape unaided from the exposure situation. Examples of symptoms that may lead to acute health effects include burning eyes, coughing, dizziness, nausea, disorientation, lack of coordination, headache, or other symptoms that manifest immediately following the exposure. If such symptoms are experienced upon entry, it is important that an evaluation be undertaken to determine if there is a possibility of health effects that could cause unconsciousness or death and as such require compliance with confined space entry requirements.

What is the connection between the phrase, "atmospheric contaminants, including gases, vapours, fumes, dusts or mists that could result in acute health effects that pose immediate threat to life or interfere with a person's ability to escape unaided from a confined space" and the phrase, "airborne contaminants with IDLH levels"?

"Atmospheric contaminants" is meant to have a similar meaning to “airborne contaminants” with IDLH (Immediately Dangerous to Life or Health) levels when referring to airborne contaminants with acute toxicity. Both relate to overexposure that could interfere with a person’s ability to escape unaided from a confined space.

IDLH is not a term defined in the Regulation, but is a term used by NIOSH (National Institute for Occupational Safety and Health) to describe levels for air contaminants in the selection of respiratory protection against airborne contaminant exposure. Generally speaking, the IDLH level of airborne contaminants is considered to be a concentration that is immediately dangerous to life or health because the IDLH concentration could cause escape-impairing symptoms or acute irreversible health effects.

Is the application of confined space provisions triggered by potential exposure to IDLH levels of air contaminants?

For a space to fall within the Regulation’s “confined space” definition, it must meet certain criteria (see section 4 of this guideline) including, a fully or partially enclosed space in which atmospheric hazards may occur because of its construction, location or contents or because of work that is done in it. Consideration of IDLH levels may be a factor in determining the criteria for atmospheric hazards.

What does ‘escape unaided’ mean?

It means being able to escape without the assistance of respiratory protection, emergency equipment or other devices, or other persons.

If measures and/or controls are taken to control hazards in a space prior to workers entering it, do we still need to consider it a confined space?

Control measures, such as continuous mechanical ventilation to ensure that the concentrations of an atmospheric hazard are controlled or maintained at an appropriate level, would not eliminate the possibility of a potential atmospheric hazard, and therefore the space would be considered a confined space.

If measures are implemented to eliminate the possibility that any atmospheric hazards may occur in a space, then the confined space provisions would no longer need to apply. Elimination of an atmospheric hazard occurring is different from the control of the hazard. If workers must enter the confined space to eliminate the hazards (steam cleaning, for example), then the regulation would apply during the cleaning process.

Every confined space can be unique and must be thoroughly evaluated to determine whether or not it is possible to eliminate the potential for an atmospheric hazard to occur.

Note that even if a space might not be a confined space under the Confined Space Regulation, the employer must take every precaution reasonable in the circumstances to protect workers entering the space, as required under clause 25(2)(h) of the OHSA.

What are the hazards of oxygen deficiency or enrichment?

If the concentration of oxygen falls below the acceptable limit of 19.5%, the space is oxygen-deficient. This hazard is a significant cause of many fatalities in confined spaces. Oxygen deficiency may occur from biological or chemical reactions such as rusting, or by displacement of oxygen by other gases.

If the concentration exceeds the limit of 23%, then the space is oxygen-enriched, increasing the likelihood of explosions or fires by increasing the potential of any combustible or flammable material to be ignited as well as the rate of reaction. Oxygen enrichment may occur from leaking gases, welding equipment, or oxygen lines that have not been blanked.

Oxygen Scale

  6% 14% 16% 19.5% 21% More than 23%
  Difficult breathing, death in minutes Faulty judgement, rapid fatigue Impaired judgement and breathing Minimum for safe entry Normal    Oxygen enriched, extreme fire hazard  

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