Confined spaces - No easy way out

This publication is intended to complement the Canada Labour Code and the Confined Spaces Regulation. It contains general information that can help you determine whether all safety measures have been taken so that you can safely enter a confined space.

Confined spaces - Definition

Part XI of the Canada Occupational Safety and Health Regulations sets standards for working in confined spaces.

"Confined space" means an enclosed or partially enclosed space that:

  1. is not designed or intended for human occupancy except for the purpose of performing work;
  2. has restricted means of access and egress; and
  3. may become hazardous to an employee entering it due to

    1. its design, construction, location or atmosphere,
    2. the materials or substances in it, or
    3. any other conditions relating to it.

Some examples of confined spaces are: manholes, sewers, boilers, tunnels, pipelines, wells, fuel tanks, ballast tanks, storage tanks, tank cars and tank trucks, vats, process vessels, septic tanks, sewage lift stations, silos, boots in grain elevators, trenches, and ventilation and exhaust ducts. Although some of these are easily recognized as confined spaces, others may not be.

Class of confined spaces

In Part XI, "class of confined spaces" means a group of at least two confined spaces that are likely, by reason of their similarity, to present the same hazards to persons entering, exiting, or occupying them.

Use the following criteria to identify a class of confined spaces:

  1. the confined spaces may be of similar size and shape;
  2. they may contain equipment and machinery that has the same or similar purpose and use;
  3. they may present similar hazards, such as:

    • restricted entry and exit;
    • probable exposure to the same or similar hazardous substances, such as: asphyxiants (these smother people), explosive gases, biological hazards (these are harmful to human cells);
    • exposure to an oxygen-deficient atmosphere;
    • exposure to hazardous substances near or surrounding the confined space;
    • possible leaks from pipes, or water entering;
    • danger of drowning or being covered in flowing material;
  4. the entry and/or emergency procedures can apply to every confined space in a class.

Duties of the employer

Before permitting any person to enter a confined space, to inspect, clean or carry out maintenance work, an employer shall provide every employee who is likely to enter a confined space with instruction and training in entry and emergency procedures and the use of protective equipment. Where there is a safety and health committee or safety and health representative, the procedures will be established in consultation with that committee or representative.

Hazard assessment

Where a confined space or class of confined spaces has not been assessed, the employer shall appoint a qualified person to:

  1. carry out an assessment of the physical and chemical hazard that the person who is entering the space may be exposed to;
  2. specify the tests to determine if the person will be exposed to any danger;
  3. submit a signed report of the findings to the employer.

The employer shall make a copy of the report for the safety and health committee or the safety and health representative.

The employer shall review the report at least every three years.

Specific hazards associated with confined spaces

Accident investigation reports show that accidents are caused when people are not well trained or fully informed about the hazards of entering confined spaces. Accident statistics suggest that about 50 percent of deaths in confined spaces have resulted from oxygen deficiency and that no testing was done in those cases.

In addition, more than half of those who die in confined spaces do so while trying to rescue their fellow workers.

There are four main dangers in confined spaces:

  • oxygen deficiency and oxygen enrichment;
  • fire and/or explosion;
  • toxicity;
  • drowning in liquids and/or entrapment in free-flowing
  • solids.

Ventilation equipment

When ventilation is used in a confined space the employer shall not grant access to any person unless the ventilation equipment is:

  1. equipped with an alarm;
  2. monitored by an employee.

Oxygen deficiency and enrichment

Many deaths in confined spaces are caused by a lack of oxygen. The only way to be sure there is enough oxygen is to carefully test with an oxygen monitor before you go in and, if the hazard assessment states that it is necessary, while you are working in the space.

There are two main causes of oxygen deficiency:

  1. Oxygen is displaced by gases such as nitrogen, an inert gas introduced to displace flammable gases when purging vessels in preparation for hot work.
  2. Oxygen is used up by:

    • combustion of flammable substances such as in welding and other hot work;
    • explosions or fires (oxygen levels may stay dangerously low long after the fire is out because the oxygen is replaced by the products of combustion);
    • chemical reactions such as rusting of metal;
    • people working in the space and using up oxygen as they breathe.

What are the effects of reduced oxygen levels?

Normal air has approximately 21 percent oxygen by volume at normal atmospheric pressure.

  • At 16 percent oxygen your judgment and breathing are impaired and you are quickly exhausted.
  • At 12 percent you become unconscious and will die unless removed to fresh air.
  • At 6 percent you have difficulty breathing and will die in seconds.

Warning! Be sure the confined space has been tested fully before you enter. Continue to test, if necessary, while you are working there. If the required air quality cannot be maintained, wear the prescribed breathing apparatus.

Oxygen enrichment

What happens when the level of oxygen is high?

An oxygen-enriched atmosphere contains more than 23 percent oxygen by volume. This will cause flammable materials, such as clothing and hair, to burn violently when ignited. Never use pure oxygen to ventilate a confined space, since an oxygen-enriched atmosphere is a fire and explosion hazard.

Fires and explosions

Combustible gases have an explosive range with a lower explosive limit (LEL) and an upper explosive limit (UEL). When the fuel and air mixture is below the LEL, or above the UEL, ignition will not take place. A gas is combustible only between its LEL and UEL. For example, methane is combustible only when mixed with air in a concentration between 5 percent and 15 percent.

Other combustible gases have different characteristics. Some have a wider range between their upper and lower explosive limits, making them even more dangerous.

Fires and explosions are serious dangers in confined spaces. Chemicals, poor ventilation, static electricity, or machinery may contribute to explosions or fires.

Hot work

"Hot work" means any work where flame is used or a source of ignition may be produced.

Unless a qualified person has determined that the work can be performed safely, hot work shall not be performed where there are concentrations of explosive or flammable hazardous substances that do not meet the prescribed standards.

If hot work is to be performed where concentrations of explosive or flammable hazardous substances exist, a qualified person shall:

  1. patrol the area surrounding the confined space;
  2. maintain a fire-protection watch;
  3. provide fire extinguishers.

Where airborne hazards are produced by the hot work, no person shall enter or occupy the confined space unless equipped with a prescribed respiratory protection device.


Toxic (poisonous) gases present two kinds of risk in a confined space:

  • chemical asphyxiation (smothering);
  • irritation to respiratory system, the skin and eyes.

Some toxic gases that are especially dangerous in confined spaces:

  1. Hydrogen sulphide (H2S), a by-product of sewage treatment, petroleum, and other industrial processes, may be encountered in mines, gas wells, sewers, and similar installations. Since hydrogen sulphide is heavier than air, it collects in low places. In low concentrations, H2S smells like rotten eggs. However this gas quickly deadens the sense of smell, leading to a false sense of security. Always remember, high concentrations of H2S are fatal.
  2. Methane (CH4 ) is highly explosive. It can leak from a gas line and is a by-product of sewage. It is also found in coal mines. Since methane displaces oxygen, it can smother workers.
  3. Sulphur dioxide (SO2 ) is colourless but has a strong smell. It is poisonous in small amounts.
  4. Carbon monoxide (CO) is a colourless, odourless, tasteless and deadly gas. It is a product of incomplete combustion, and a common source is internal combustion engines. Overexposure may cause ringing in the ears, nausea, headache, and sleepiness. Carbon monoxide can be fatal in very low concentrations.

Remember! Engine exhaust gases contain carbon monoxide, carbon dioxide, and other harmful gases. Keep them away from openings of confined spaces where people are working.

Test carefully for toxic cases before entering a confined space

Warning! One of the biggest mistakes you can make is to ignore or not believe your test equipment. If a gas detector alarm sounds, get out even if you don't notice anything wrong.

Test equipment is designed to detect hazardous conditions long before you can. It can save your life!

Do not enter a confined space if your employer has not had a qualified person establish entry procedures for the confined space or class of confined spaces and if you have not been trained in these procedures and in the use of any testing or safety equipment to be used in the confined space.

Drowning in liquids or entrapment in free-flowing solids

Some examples are:

  • water in a tank;
  • grain in a silo;
  • earth falling into a trench or excavation.

Confined space entry

When a person is about to enter a confined space, the employer shall appoint a qualified person to verify:

  1. by tests, that compliance can be achieved for the period that the person will be in the confined space;
  2. that all free-flowing solids and liquids have been removed.

A good rule to follow:

If you can't test,

If you can't ventilate,

If you don't have breathing apparatus,

If you don't have an entry procedure,

Don't go in!

The qualified person shall submit a signed report notifying the employer of the results of the verification, including the test methods, test results, and the equipment used.

The employer shall make a copy of the report available to the safety and health committee or safety and health representative.

Emergency procedures and equipment

When conditions in a confined space cannot be complied with, the employer shall:

  1. consult with the safety and health committee or representative to establish emergency procedures;
  2. provide protective equipment;
  3. ensure that a qualified person trained in the entry and emergency procedures is in attendance outside the confined space;
  4. ensure that the qualified person is in communication with the person inside the confined space;
  5. provide the qualified person with a suitable alarm for summoning assistance;
  6. ensure that two or more persons are in the immediate vicinity of the confined space to assist in the event of an emergency;
  7. ensure that the person in the confined space is wearing an appropriate safety harness that is attached to a secure anchor outside the confined space and attached to a mechanical lifting device; and
  8. keep records.

If you notice changes in how you feel, get out of the confined space! A few seconds can be the difference between life and death. Workers die in the short time it takes to pick up a tool from the bottom of a tank. Wear the prescribed respirator and personal protective equipment only if you have been trained in their use and if the employer has taken all the necessary safety measures.

Suggested checklist for confined spaces

Temporarily unavailable.

For further information and assistance concerning work in confined spaces, contact your nearest Human Resources Development Canada - Labour Program office.

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