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What is a confined space?

Confined space

From time to time, Workplace Health and Safety Queensland receives enquiries as to the definition of a confined space under the Work Health and Safety Regulation 2011. As new construction methods and technologies arise, so do new types of confined spaces that can test the definition.

This article explains what confined spaces are to make it easier for you to identify them. That way you'll know when to comply with the relevant safety regulations. It expands on the guidance provided in the Confined Spaces Code of Practice 2011.

Defining and identifying a confined space

In the Regulation, a confined space is defined as follows:

confined space means an enclosed or partially enclosed space that:

  (a) is not designed or intended primarily to be occupied by a person; and
(b) is, or is designed or intended to be, at normal atmospheric pressure while any person is in the space; and
(c) is or is likely to be a risk to health and safety from:
   (i) an atmosphere that does not have a safe oxygen level; or
(ii) contaminants, including airborne gases, vapours and dusts, that may cause injury from fire or explosion; or
(iii) harmful concentrations of any airborne contaminants; or
(iv) engulfment;
  but does not include a mine shaft or the workings of a mine.

Note: the above definition can be found in Schedule 19 (Dictionary) of the Regulation.

This somewhat complex definition is often misunderstood. That's led to instances of workers/supervisors in control of a confined space failing to identify it, and allowing people to enter the area without the necessary precautions in place.

In order to be classified a confined space, it must be an enclosed or partially enclosed space and both clauses (a) and (b) must be true and at least one of (i), (ii), (iii) and (iv) must also be true.

Here's some more information regarding the clauses.

(a) - This clause refers to the primary purpose of the space. In order to clarify whether a space is designed or intended primarily to be occupied by a person, it helps to write down or state the name and primary function of the space is. For example:

Name of space Primary function
Trunk Water Main Carry water from the pumping station to town
Sewer Main Collect sewerage from sewer branches and carry it to the pumping station
Septic Tank Collect sewerage from house and store it
Water tank Store water for domestic use
Office House desks, office equipment and office workers

This helps determine which spaces are not designed or intended primarily to be occupied by a person. The fact that a space can be made to accommodate a person for maintenance or inspection is not the same as it being designed or intended primarily to be occupied by a person, and is secondary to the designed or intended purpose.

For example; you can’t argue that a 1.8m diameter sewer pipe is not a confined space because it is intended that during construction the sewer will be entered for inspection. This is incidental and secondary to its primary purpose, which is to carry sewerage.

(b) - This clause exempts special spaces such as hyperbaric chambers for medical use from being classified as a confined space under the Regulation. These operate above atmospheric pressure while occupied by a person and are controlled by Queensland Health. Equipment that normally operates above or below atmospheric pressure such as pipes, boilers and pressure vessels is not exempt as these spaces need to be brought to atmospheric pressure before a person can enter and remain at atmospheric pressure while occupied.

(c) - This clause specifies the types of hazards that would mean an area would be classified a confined space. The wording is sometimes misunderstood to mean that one or more of the specified hazards is likely to be present. However, the intent of the clause is to identify whether or not there is, or is likely to be, a risk (however small) to a person’s health or safety arising from one or more of the hazards (i) to (iv).

To better understand clause (c), consider a large water main that’s been drained and isolated to allow a worker to enter to inspect and make repairs to the lining. This worker isn’t likely to be engulfed by water as the water supply will have been isolated by valves or other means. However, there is still a small risk of engulfment as the isolation could fail, allowing water to enter. Therefore the space must be classified as a confined space, assuming clause (a) and (b) are true.

Here is more detail on the specific hazard types:

(i) an atmosphere that does not have a safe oxygen level has an oxygen concentration outside of the range 19.5% – 23.5% (normal atmosphere is 21%). Lower levels can lead to impaired consciousness, unconsciousness and death. Higher levels significantly increase the intensity and likelihood of fires.

The causes of changed oxygen levels in confined spaces are well known and include:

  • oxygen depletion due to biological activity, particularly in sewer systems
  • oxygen depletion due to chemical reactions, e.g. rusting steel plates
  • displacement of air by a heavier than air gas e.g. carbon dioxide from a diesel generator exhaust or natural underground sources seeping into below ground spaces
  • oxygen depletion from internal combustion engines
  • inert gas purging
  • argon gas leaking from MIG/TIG welding equipment
  • oxygen enrichment from leaking oxygen bottles.

Below ground spaces that normally contain water such as pits, sumps, sewers, shafts, tanks etc. are particularly at risk of low oxygen due to chemical and biological activity, and it’s hard to rule out the risk of oxygen depletion.

(ii) refers to contaminants that could cause a fire or explosion, and includes sources such as:

  • flammable liquids: including solvents, paints, glues, cleaners etc
  • flammable gases such as hydrogen and methane generated by chemical or biological processes
  • methane (natural gas) from natural seeps, particularly in below ground spaces
  • leaks from oxy-acetylene welding gear
  • combustible dusts such as coal dust or dusts generated from the grinding or sandblasting of paints or plastic coatings.

Below ground spaces that normally contain water such as pits, sewers, shafts, tanks etc. are at risk of accumulating flammable gas due to chemical and biological activity or natural seeps, it's generally hard to completely rule out this risk.

A person must not enter a confined space unless the level of any flammable contaminant is below 5% of the lower explosive limit (some exceptions to this are detailed in the confined space code of practice).

(iii) refers to contaminants that are toxic and can lead to poisoning in small concentrations from sources including:

  • hydrogen sulphide (rotten egg) gas generated by biological activity, particularly in sewers
  • carbon monoxide generated by internal combustion engines
  • paints, solvents, glues, cleaners
  • welding fumes.

(iv) engulfment means to be swallowed up in, or be immersed by, liquid or solid, which may result in asphyxiation or drowning. Potential causes of engulfment include:

  • influx of mud, soil or ground water due to collapse or partial collapse of a tunnel/pit/shaft walls/shoring
  • flash flooding
  • failure or inadvertent operation of an isolation device (e.g. valve) causing an influx of liquid (water, sewerage etc.) from connected pipes or vessels
  • bursting of water pipes running through an access tunnel.

People entering below ground spaces are particularly at risk of engulfment because there is constant hydrostatic pressure in the soil or groundwater surrounding the space. It is generally hard to completely rule out the risk of engulfment in these spaces.

Risk assessments are essential

The Regulation requires a risk assessment to be conducted once a confined space has been identified. However, for cases where a confined space is suspected (clause (a) and (b) true) and it is not clear whether there is a risk to health and safety from any of the hazard types (i) to (iv), a risk assessment can help to identify the presence of these hazards.

The consequences of any of the hazard types (i) to (iv) materialising in a confined space can be serious or fatal, and the rescue of workers often difficult and dangerous. As such, if there is doubt as to the classification of a confined space, it’s best to be conservative and treat it as a confined space.

For any below ground space, it may not be possible to rule out the risk of atmospheric contamination or engulfment, therefore these spaces should generally be considered to be confined spaces.

Domestic roof cavities and crawl spaces

Roof cavities and under-floor crawl spaces in domestic houses are generally not classified as confined spaces as there is negligible risk of atmospheric contamination or engulfment if a person enters to perform work or inspection. However, if certain hazards are introduced (gas flame brazing torches or flammable solvents), then a risk to health and safety from atmospheric contamination may arise and the space could be classified as a confined space.

Anyone planning to enter a roof cavity or crawl space should consider what hazards might be present or introduced when they enter. The space should be classified accordingly.

It should be noted that leaks from small propane or MAP gas cylinders have caused serious explosions in work vehicles and the same could happen in a roof cavity or crawl space.

Of course, when you're working in confined spaces you are not immune from the general dangers of your job such as exposure to UV (solar and welding), asbestos, trenching (possible collapse), hazardous chemicals, falls, manual tasks and underground services (power, gas, water etc.).

Further information

Last updated
01 March 2017

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