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Confined space environment

Hazard Knowledge

It is not possible to provide a comprehensive list of confined spaces. Some spaces may become confined when work is carried out, or during their construction, fabrication or subsequent modification.

The Confined Spaces Regulations and the Confined Spaces Regulations (Northern Ireland) set out the definition of what constitutes a confined space. However, identifying environments that fall within the legal definition is not always that easy, especially when confronted with a rapidly escalating or complex incident.

The associated confined space regulations state a confined space must have both of the following defining features:

  • It must be a space that is substantially (though not always entirely) enclosed
  • One or more of the specified risks must be present or reasonably foreseeable

The specified risks are:

  • Serious injury through fire or explosion
  • Loss of consciousness arising from increased body temperature
  • Loss of consciousness or asphyxiation arising from gas, fume, vapour or lack of oxygen
  • Drowning from an increase in the level of a liquid
  • Asphyxiation arising from a free-flowing solid or being unable to reach a respirable environment due to entrapment by a free-flowing solid

Explosive atmospheres

The Dangerous Substances and Explosive Atmospheres Regulations and The Dangerous Substances and Explosive Atmospheres Regulations (Northern Ireland) (DSEAR) define an ‘explosive atmosphere’ as a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapours, mists or dusts in which, after ignition has occurred, combustion spreads to the entire unburned mixture.

Whereas a ‘potentially explosive atmosphere’ means an atmosphere which could become explosive due to local and operational conditions.

The definition of a confined space includes a specified risk of 'serious injury due to fire or explosion'. These can arise from:

  • Presence of flammable substances
  • Excess oxygen in the atmosphere
  • Presence of chemicals that can combust or spark in enriched or, in some cases, normal oxygen levels
  • Ignition of combustible dusts
  • Leaks from adjoining on-site machinery or processes that have not been effectively isolated
  • Inappropriate ventilation
  • Inappropriate ventilation of a flammable or explosive atmosphere may create additional hazards. For further information refer to Hazardous materials physical hazards - Flammable vapours: Unignited

Extremes of temperature or humidity

The legislation refers to the specified risk of 'loss of consciousness arising from increased body temperature'. This could be the result of high atmospheric temperatures, humidity or a range of other factors.

Working in hot conditions can lead to a dangerous rise in core body temperature; in extreme cases, this could lead to unconsciousness. This can be worsened by:

  • Wearing personal protective equipment (PPE)
  • Highly physical or strenuous work

Excessive heat can occur where:

  • Work is being carried out in hot conditions
  • The confined space is exposed to a significant heat source
  • Processes are being undertaken that generate significant amounts of residual heat

For further information refer to:

Toxic or asphyxiating atmospheres

Also known as irrespirable atmospheres are caused by the presence of toxic gases or vapours, or the lack of sufficient oxygen. Working in this type of atmosphere can lead to asphyxia, unconsciousness or death.

Environments where asphyxiant gases may be present include:

  • Where contaminants have been processed or stored
  • Where there is sewage, sludge or other deposits, especially if gases are released when it is disturbed
  • In spaces where contaminants can enter, or are produced by equipment in use
  • Where exhaust gases from engine driven equipment, machinery or vehicles have accumulated
  • Where naturally occurring, biological processes produce toxic gases, especially in poorly- ventilated spaces
  • Where gases from leaks, failure or damage to machinery, pipes or cylinders have accumulated
  • In spaces such as pipes, sewers or manholes

Oxygen deficiency can occur naturally, result from industrial processes or the storage of products, including:

  • Purging confined spaces with an inert gas to remove flammable or toxic gases, vapours or aerosols
  • Naturally occurring biological or chemical processes that consume oxygen
  • Transportation or storage of wood pellets, used as a biofuel, which may consume oxygen and produce carbon monoxide gas
  • When spaces are left completely closed or poorly ventilated for extended periods
  • Limestone chippings, associated with drainage operations, that can produce increased levels of carbon dioxide when they get wet
  • Burning operations and work, such as welding and grinding, which consume oxygen
  • Displacement of air during pipe freezing
  • The gradual depletion of oxygen as workers breathe in confined spaces, if there is an inadequate supply of replacement air

The intentional reduction of oxygen, to create a hypoxic atmosphere, can be used to:

  • Inhibit or suppress fire, using Redox or gaseous systems – for further information refer to the BRE supplementary information
  • Extend the shelf life of produce
  • Reduce the effects of oxidation

Water or other liquids

The legislation refers to the risk of drowning from an increase in the level of a liquid. This could be a result of the hazard of ingress of water or other liquids.

Liquids can flow into a confined space and lead to drowning; for example, the ingress of liquid, when working in sewers or from other processes, that has not been adequately isolated in an industrial situation.

Liquids may obscure other hazards, such as machinery, objects, obstructions, changes in levels or openings. Liquids may also obscure access and egress routes.

The presence of a liquid can also lead to death, serious injury, hypothermia or have an effect on health, depending on the nature of the liquid, such as its corrosiveness or toxicity.

Free-flowing solids

The legislation refers to the risk of asphyxiation arising from a free-flowing solid or being unable to reach a respirable environment due to being trapped by such a free-flowing solid. This could be due to the ingress of free-flowing solids.

Free-flowing solids have similar characteristics to liquids and can submerge a person, preventing them from breathing. These solids include grain, sugar, flour, sand, coal dust and other substances in powder or granular form, such as gravel or soil being disturbed due to digging actions.

In a confined space, the risk is increased because there is no space for the material to flow away and actions that may introduce a sprcific risk as using a petrol saw which would induce fumes.

Some free-flowing solids may form combustible dust clouds when disturbed; this could present a risk of explosion For further information refer to Hazardous materials: Combustible dust.

Ineffective communications

In some confined space environments, distance, interference and barriers may make normal communications ineffective.

Working at height in a confined space

Some confined spaces involve access to the area from above, using work at height access equipment. Personnel may be deployed in areas where there are unprotected edges and therefore a risk of falling.

Some of the above conditions may already be present in the confined space. However, some may arise from the work being carried out, or because of ineffective isolation of industrial sites or processes, or leakage from a pipe connected to the confined space.

Other hazards, not specific to confined spaces, can include:

These should be identified when risk assessing the need to enter or work in a confined space. These hazards are not unique to confined spaces working and are not dealt with in the confined space regulations, however they are covered in other sections of guidance. If these hazards are present in a confined space, the precautions will almost always be more extensive because of the enclosed nature of the confined space.

Personnel should be aware that the physical environment of a confined space can take many forms and that a variety of techniques and skill sets are required to overcome the challenges they may present. Challenges include difficult access and egress, restricted spaces, slopes, gradients, changing levels, narrow apertures, different types of surface and poor lighting.