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Confined Spaces (GUIDANCE)

(Revised 26th September 2003)



  1. Introduction
  2. What is a Confined Space?
  3. What are the dangers from confined spaces?
  4. What the law states
  5. Avoid entering confined spaces
  6. Safe Systems of Work
  7. Appointment of a Supervisor
  8. Are persons suitable for the work?
  9. Isolation
  10. Cleaning before entry
  11. Check the size of the entrance
  12. Provision of ventilation
  13. Testing the air
  14. Provision of breathing apparatus
  15. Preparation of emergency arrangements
  16. Provision of rescue harnesses
  17. Communications
  18. Check how the alarm is raised
  19. Is a 'Permit-to-Work' necessary?
  20. Emergency Procedures
  21. Guidance Documents


The following section is based on the HSE Guidance Leaflet entitled "Safe Work in Confined Spaces".

What is a confined space?

It can be any space of an enclosed nature where there is a risk of death or serious injury from hazardous substances or dangerous conditions (e.g. lack of oxygen).

Some confined spaces are fairly easy to identify, e.g. enclosures with limited openings:

* storage tanks;

* silos;

* reaction vessels;

* enclosed drains;

* sewers.

Others may be less obvious, but can be equally dangerous, for example:

* open-topped chambers;

* vats;

* combustion chambers in furnaces etc;

* ductwork;

* unventilated or poorly ventilated rooms.

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

What are the dangers from confined spaces?

Dangers can arise in confined spaces because of:

  1. A lack of oxygen;This can occur:
    • where there is a reaction between some soils and the oxygen in the atmosphere;
    • following the action of ground water on chalk and limestone which can produce carbon dioxide and displace normal air;
    • in ships' holds, freight containers, lorries, etc., as a result of the cargo reacting with oxygen inside the space;
    • inside steel tanks and vessels when rust forms.
    • Poisonous gas, fume or vapour.
    • These can:
      • build-up in sewers and manholes and in pits connected to the system;
      • enter tanks or vessels from connecting pipes;
      • leak into trenches and pits in contaminated land, such as old refuse tips and old gas works.
  2. Liquids and solids which can suddenly fill the space, or release gases into it, when disturbed. Free flowing solids such as grain can also partially solidify or 'bridge' in silos causing blockages which can collapse unexpectedly.
  3. Fire and explosions (e.g. from flammable vapours, excess oxygen, etc.).
  4. Residues left in tanks, vessels, etc., or remaining on internal surfaces which can give off gas, fume or vapour.
  5. Dust may be present in high concentrations, e.g. in flour silos.
  6. Hot conditions leading to a dangerous increase in body temperature.

Some of the above conditions may already be present in the confined space. However, some may arise through the work being carried out, or because of ineffective isolation of plant nearby, e.g. leakage from a pipe connected to the confined space. The enclosure and working space may increase other dangers arising through the work being carried out, for example:

  • achinery being used may require special precautions, such as provision of dust extraction for a portable grinder, or special precautions against electric shock;

  • gas, fume or vapour can arise from welding, or by use of volatile and often flammable solvents, adhesives, etc.;

  • if access to the space is through a restricted entrance, such as manhole, escape or rescue in an emergency will be more difficult (see Emergency Procedures)

What the law says

You must carry out a suitable and sufficient assessment of the risks for all work activities for the purpose of deciding what measures are necessary for safety (The Management of Health and Safety at Work Regulations 1999, Regulation 3). For work in confined spaces this means identifying the hazards present, assessing the risks and determining what precautions to take. In most cases the assessment will include consideration of:

* the task;

* the working environment;

* working materials and tools;

* the suitability of those carrying out the task;

* arrangements for emergency rescue.

The HSE leaflet entitled 5 Steps to Risk Assessment will help you further. You may need to appoint competent people to help manage the risks and ensure that employees are adequately trained and instructed (The Management of Health and Safety at Work Regulations 1999, Regulation 6). Of course, you may be the best person to do this, however, you may need to train someone else or engage the services of a competent person for additional help.

If your assessment identifies risks of serious injury from work in confined spaces, such as the dangers highlighted above, the Confined Spaces Regulations 1997 apply. These regulations contain the following key duties:

* avoid entry to confined spaces, e.g. by doing the work from outside;

* if entry to a confined space is unavoidable, follow a safe system of work; and

* put in place adequate emergency arrangements before the work starts.

These duties, and what you need to do, are further described in this leaflet.

Avoid entering confined spaces

You need to check if the work can be done another way so that entry or work in confined spaces is avoided. Better work-planning or a different approach can reduce the need for confined space working.

Ask yourself if the intended work is really necessary, or could you:

  • modify the confined space itself so that entry is not necessary;
  • have the work done from outside, for example:
    • blockages can be cleared in silos by use of remotely operated rotating flail devices, vibrators or air purgers;
    • inspection, sampling and cleaning operations can often be done from outside the space using appropriate equipment and tools;
    • remote cameras can be used for internal inspection of vessels.

Safe systems of work

If you cannot avoid entry into a confined space make sure you have a safe system for working inside the space.

Use the results of your risk assessment to help identify the necessary precautions to reduce the risk of injury. These will depend on the nature of the confined space, the associated risk and the work involved.

Make sure that the safe system of work, including the precautions identified, is developed and put into practice. Everyone involved will need to be properly trained and instructed to make sure they know what to do and how to do it safely.

The following checklist is not intended to be exhaustive but includes many of the essential elements to help prepare a safe system of work.

Appointment of a Supervisor

Supervisors should be given responsibility to ensure that the necessary precautions are taken to check safety at each stage and may need to remain present while work is underway.

Are persons suitable for the work?

Do they have sufficient experience of the type of work to be carried out, and what training have they received? Where risk assessment highlights exceptional constraints as a result of the physical layout, are individuals of suitable build? The competent person may need to consider other factors, e.g. concerning claustrophobia or fitness to wear breathing apparatus, and medical advice on an individual's suitability may be needed.


Mechanical and electrical isolation of equipment is essential if it could otherwise operate, or be operated, inadvertently. If gas, fume or vapour could enter the confined space, physical isolation of pipework etc. needs to be made. In all cases a check should be made to ensure isolation is effective.

Cleaning before entry

This may be necessary to ensure fumes do not develop from residues etc. while the work is being done.

Check the size of the entrance

Is it big enough to allow workers wearing all the necessary equipment to climb in and out easily, and provide ready access and egress in an emergency? For example, the size of the opening may mean choosing air-line breathing apparatus in place of self-contained equipment which is more bulky and therefore likely to restrict ready passage.

Provision of ventilation

You may be able to increase the number of openings and therefore improve ventilation. Mechanical ventilation may be necessary to ensure an adequate supply of fresh air. This is essential where portable gas cylinders and diesel-fuelled equipment are used inside the space because of the dangers from build-up of engine exhaust.

Warning: Carbon monoxide in the exhaust from petrol-fuelled engines is so dangerous that use of such equipment in confined spaces should never be allowed.

Testing the air

This may be necessary to check that it is free from both toxic and flammable vapours and that it is fit to breathe. Testing should be carried out by a competent person using a suitable gas detector which is correctly calibrated. Where the risk assessment indicates that conditions may change, or as a further precaution, continuous monitoring of the air may be necessary.

Provision of breathing apparatus

This is essential if the air inside the space cannot be made fit to breathe because of gas, fume or vapour present, or lack of oxygen. Never try to 'sweeten' the air in a confined space with oxygen as this can greatly increase the risk of a fire or explosion.

Preparation of emergency arrangements

This will need to cover the necessary equipment, training and practice drills.

Provision of rescue harnesses

Lifelines attached to harnesses should run back to a point outside the confined space.


An adequate communications system is needed to enable communication between people inside and outside the confined space and to summon help in an emergency.

Check how the alarm is raised

Is it necessary to station someone outside to keep watch and to communicate with anyone inside, raise the alarm quickly in an emergency, and take charge of the rescue procedures?

Is a 'permit-to-work' necessary?

A permit-to-work ensures a formal check is undertaken to ensure all the elements of a safe system of work are in place before people are allowed to enter or work in the confined space. It is also a means of communication between site management, supervisors, and those carrying out the hazardous work. Essential features of a permit-to-work are:

  • clear identification of who may authorise particular jobs (and any limits to their authority) and who is responsible for specifying the necessary precautions (e.g. isolation, air testing, emergency arrangements, etc.);

  • provision for ensuring that contractors engaged to carry out work are included;

  • training and instruction in the issue of permits;

  • monitoring and auditing to ensure that the system works as intended.

Emergency Procedures

When things go wrong, people may be exposed to serious and immediate danger. Effective arrangements for raising the alarm and carrying out rescue operations in an emergency are essential.

Contingency plans will depend on the nature of the confined space, the risks identified and consequently the likely nature of an emergency rescue.

Emergency arrangements will depend on the risks. You should consider:

Communications - How can an emergency be communicated from inside the confined space to people outside so that rescue procedures can start? Don't forget night and shift work, weekends and times when the premises are closed, e.g. holidays. Also, consider what might happen and how the alarm can be raised.

Rescue and resuscitation equipment - Provision of suitable rescue and resuscitation equipment will depend on the likely emergencies identified. Where such equipment is provided for use by rescuers, training in correct operation is essential.

Capabilities of rescuers - There need to be properly trained people, sufficiently fit to carry out their task, ready at hand, and capable of using any equipment provided for rescue, e.g. breathing apparatus, lifelines and fire-fighting equipment. Rescuers also need to be protected against the cause of the emergency.

Guidance Documents

Approved Code of Practice (ACOP), "Safe work in confined spaces" (1997) HSC

Leaflet entitled "Safe Work in Confined Spaces" INDG258 (2003) HSE


Environmental Health and Safety Services contact details

University of St Andrews
Bute Building Queens Terrace
St Andrews
KY16 9TS
Scotland, United Kingdom

Tel: +44 (0)1334 462750
Fax:44 (0)1334 462747