MRO Magazine

The Dangers of Confined Spaces

Confined spaces are one of the least-liked places to do maintenance work. They're usually awkward to access and tight to move in, and it's a pain getting all your tools and supplies in and out. Yet wo...

Health & Safety

April 1, 2007
By Simon Fridlyand

Confined spaces are one of the least-liked places to do maintenance work. They’re usually awkward to access and tight to move in, and it’s a pain getting all your tools and supplies in and out. Yet working in them is one of the realities of the job.

A confined space is defined as one that is substantially enclosed (though not always entirely), and where serious injury can occur from hazardous substances or conditions within the space or nearby (e.g. a lack of oxygen).

A number of people are killed or seriously injured in North America each year in confined spaces. These accidents occur across a wide range of industries, from those involving a complex plant through to simple storage vessels. Those killed include not only people working in the confined spaces but those who try to rescue them without having proper training or equipment. (According to the National Institute for Occupational Safety and Health in the U.S., more than 60% of confined space fatalities occur among would-be rescuers.)

The definition of a confined space is consistent across all regulations. For example, Ontario regulation 629/05 in section 119 defines a ‘confined space’ as a fully or partially enclosed space:


1. that is not both designed and constructed for continuous human occupancy, and

2. in which atmospheric hazards may occur because of its construction, location or contents, or because of work that is done in it.

Confined spaces can include storage tanks, process vessels, boilers, silos, storage bins, pits, pipes, sewers, tunnels and shafts. Any place of work where the atmosphere is liable to be contaminated at any time by dust, fumes, mist, vapour, gas or other harmful substance, or is liable at any time to be oxygen-deficient, is defined as a confined space.

When the work area is not subject to good natural ventilation, people can be readily exposed to harmful vapours or suffer lack of oxygen, and collapse as a result. People entering the same space to rescue colleagues may become the next victims.

Confined spaces can be potentially hazardous because of the presence of one or a combination of:

* known waste contaminants (sewerage, etc.)

* suspected, unidentified gas contaminants (possibly H2S or methane)

* poor or no ventilation (oxygen deficient or a high CO or CO2 atmosphere)

* dangerous or difficult access

* poor or inadequate lighting

* the possibility of sudden or uncontrolled flow variations, or

* hazardous substances.

Confined spaces are not meant for continuous occupancy, and are likely to be entered only for purposes such as inspection, maintenance or construction. Limited entry and exit points not only make escape or rescue difficult, but also can restrict natural ventilation.

Confined vs. enclosed space

A confined space, where workers may find ordinary job hazards intensified, is different from an enclosed space, which is any area enclosed on all sides and overhead, such as a machinery room, storage facility or boiler room. Enclosed spaces may be meant for frequent or lengthy human occupancy, and often have accessible points of entry and exit. Requirements for safe entry to enclosed areas are usually less strict than for confined spaces.

If a confined space exists, health and safety regulations mandate a program for dealing with the issue. A confined space program is a written document that includes: a method for recognizing each confined space to which the program applies, a method for assessing the hazards to which workers may be exposed, a method for the development of confined space entry plans (which include on-site rescue procedures), a method for training workers, and an entry permit system.

Hazard assessment includes identification and assessment of all potential hazards that may exist at the beginning of the work, as well as those that may develop because of the work activities.

A written entry plan must be developed by a competent person before any worker enters a confined space. The plan must include procedures for the control of hazards identified in the assessment. It also shall contain provisions for: the duties of workers responsible for on-site rescue procedures, rescue equipment and methods of communication; personal protective equipment; clothing and devices; isolation of energy and control of materials movement; attendants; adequate means for entering and exiting; atmospheric (air quality) testing; adequate procedures for working in the presence of explosive or flammable substances; ventilation and purging.

Plan-specific training is required for every worker who enters a confined space or who performs related work. The training must explain how to work safely and properly, and how to follow the plan.

The employer must maintain up-to-date written records showing who provided and who received training, and the date when it was provided. The records may be incorporated into an entry permit.

Entry permits need to be issued by employers. A separate entry permit is to be issued each time work is to be performed in a confined space, before any worker enters the confined space. An entry permit must include at least the following:

1. The location of the confined space.

2. A description of the work to be performed there.

3. A description of the hazards and the corresponding control measures.

4. The time period for which the entry permit applies.

5. The name of the attendant.

6. A record of each worker’s entries and exits.

7. A list of the equipment required for entry and rescue, and verification that the equipment is in good working order.

8. Results obtained in atmospheric (air quality) testing.

More information on working safely in confined spaces can be found at By following the requirements of confined space regulations, the number of workers who are injured or killed in confined spaces can clearly be reduced.

Click here for the Safety Entry Checklist

Safety editor Simon Fridlyand, P.Eng., is president of S.A.F.E. Engineering, a Toronto-based company specializing in industrial health and safety issues and PSR compliance. He can be reached 416-447-9757 or For more information, visit