Many workplaces contain areas that are considered “confined spaces” because while they are not necessarily designed for people, they are large enough for workers to enter and perform certain jobs. A confined space also has limited or restricted means for entry or exit and is not designed for continuous occupancy. Confined spaces include, but are not limited to, tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, tunnels, equipment housings, ductwork, pipelines, etc.

OSHA uses the term “permit-required confined space” (permit space) to describe a confined space that has one or more of the following characteristics: contains or has the potential to contain a hazardous atmosphere; contains material that has the potential to engulf an entrant; has walls that converge inward or floors that slope downward and taper into a smaller area which could trap or asphyxiate an entrant; or contains any other recognized safety or health hazard, such as unguarded machinery, exposed live wires, or heat stress.

Confined Space refers to any place, including any vessel, tank, container, pit, bund, chamber, cellar or any other similar space which, by virtue of its enclosed nature, creates conditions that give rise to a likelihood of an accident, harm or injury of such a nature as to require emergency action due to

  • the presence or reasonably foreseeable presence of:
    –    flammable or explosive atmospheres
    –    harmful gas, fume or vapour
    –    free flowing solid or an increasing level of liquid
    –    excess of oxygen
    –    excessively high temperature
  • the lack or reasonably foreseeable lack of oxygen

The key characteristics of a confined space are:

  • the space must be substantially enclosed
  • there must be a risk of at least one of the hazards listed above occurring within the space
  • the risk of serious injury from the hazard must be created by virtue of the enclosed nature of the space
  • the potential injury must be serious and be such as to require emergency action to rescue the person involved.

What are the hazards associated with confined spaces?

TOXIC ATMOSPHERE: A toxic atmosphere may cause various acute effects, including impairment of judgement, unconsciousness and death. A toxic atmosphere may occur due to the presence or ingress of hazardous substances. These substances may be present in the Confined Space for various reasons such as:

  • remaining from previous processing or storage
  • arising from the disturbance of sludge and other deposits
  • the presence of a fire or flames within the space
  • seepage from improperly isolated adjoining plant
  • formation during the work processes carried out in the space
  • being released from under scale and in brickwork as a result of the work process

OXYGEN DEFICIENCY: Oxygen can be lacking in a confined space for the following reasons:

  • displacement of air by another gas
  • various biological processes or chemical reactions (such as rotting of organic matter, rusting of metals, burning, etc)
  • absorption of air onto steel surfaces, especially where these are damp

Oxygen Enrichment: An excess of oxygen, in the presence of combustible materials, results in an increased risk of fire and explosion. Some materials, which do not burn in air, may burn vigorously or even spontaneously in an enriched oxygen atmosphere.

Flammable or Explosive Atmospheres: A flammable atmosphere presents a risk of fire or explosion. Such an atmosphere can arise from the presence in the confined space of flammable liquids or gases or of a suspension of combustible dust in air. If a flammable atmosphere inside a confined space ignites, an explosion may occur, resulting in the expulsion of hot gases and the disintegration of the structure.

Flowing Liquid or Free Flowing Solids: Liquids or solids can flow into the confined space causing drowning, suffocation, burns and other injuries.  Solids in powder form may also be disturbed in a confined space resulting in an asphyxiating atmosphere.

Excessive Heat: The enclosed nature of a confined space can increase the risk of heat stroke or collapse from heat stress, if conditions are excessively hot. The risk may be exacerbated by the wearing of personal protective equipment or by lack of ventilation.