Introduction to working in confined spaces

A confined space is one which is both enclosed or largely enclosed and has a reasonably foreseeable specified risk to workers of:

  • fire
  • explosion
  • loss of consciousness
  • asphyxiation
  • drowning

It may be small and restrictive for the worker or it could be far larger such as a grain storage silo with hundreds of cubic metre capacity.


Working in a confined space is dangerous because of the risks from noxious fumes, reduced oxygen levels, or a risk of fire.

Other dangers may include flooding, drowning or asphyxiation from some other source such as dust, grain or other contaminant.

What you have to do

Wherever possible, you should avoid carrying out tasks in confined spaces. If this is not possible, you must assess the risks of the particular confined space and plan how you will control those risks. For example, if:

  • a confined space has harmful fumes, you should consider how these can be ventilated or removed
  • there is a risk of liquids or gases flooding in, you should establish whether the valves can be locked shut
  • someone is going into a confined space and there is not enough oxygen to breathe properly, you must provide breathing apparatus or ventilate the space to increase oxygen levels before entering

You should have emergency arrangements where necessary. If someone is working in a confined space, think about the following:

  • how will you know they are okay and have not been overcome by fumes?
  • how will you get them out if they are overcome? (It’s not enough to rely on the emergency services)


  • be aware of the risks that may occur within a confined space
  • make sure the person doing the work is capable and trained in both the work and the use of any emergency equipment

Do not

  • work in confined spaces unless it's essential to do so
  • ignore the risks – just because a confined space is safe one day does not mean it will always be
  • let others enter a confined space until you are sure it's safe to do so


Crane compartment

Having identified a fault in a crane's hydraulics, 2 men accessed a closed compartment. Within a minute of entering the compartment, one had passed out and the other was feeling lightheaded but managed to escape. Two others entered and tried to save the first man but were both overcome.

The 3 men were extracted by the emergency service but 2 of them died.

How it could have been avoided

Water had got into the compartment causing rusting, which depleted the oxygen levels. Had the oxygen levels been checked, the space could have been ventilated and the deaths could have been avoided.

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Updated 2023-04-20