What to consider when assessing the risks of a confined space

Carry out a suitable and sufficient assessment of the risks of all work activities to decide what measures are needed for safety. For work in confined spaces, this means identifying the hazards, assessing the risks and deciding what precautions to take. In most cases the assessment will consider:

• the task
• the working environment
• working materials and tools
• the suitability of the people carrying out the task
• arrangements for emergency rescue

Precautions to include in a safe system of work for confined spaces

First, check whether the work can be done another way that avoids entering or working in a confined space. Better planning or a different approach can reduce the need. Ask whether the work is really necessary, or whether you could:

• modify the confined space itself so that entry is not needed
• use a competently assessed method from outside where possible, such as remote inspection or designed clearing equipment. Silo blockages need specialist assessment: vibration or air injection can release material, pressure or combustible dust and must not be improvised

If entry cannot be avoided, make sure there is a safe system of working inside the space. The precautions below are not exhaustive, but they include many of the essential elements of a safe system of work.

• Appointment of a supervisor. Give supervisors the responsibility of making sure the necessary precautions are taken and of checking safety at each stage. They may need to stay present while work is going on.
• Suitability of people. Do they have enough experience of the type of work, and what training have they had? Where the assessment shows exceptional constraints from the physical layout, are the individuals of suitable build? The competent person may need to consider other factors, such as claustrophobia or fitness to wear breathing apparatus, and may need medical advice on an individual's suitability.
• Isolation. Mechanical and electrical isolation of equipment is essential if it could otherwise operate, or be operated, by accident. If gas, fume or vapour could enter the space, the pipework must be isolated. In every case, check that the isolation is effective.
• Cleaning before entry. This may be needed to make sure that fumes do not develop from residues while work is under way.
• Check the size of the entrance. Is it big enough for workers wearing all the necessary equipment to climb in and out easily, and to get in and out quickly in an emergency? The size of the opening may mean choosing air-line breathing apparatus instead of self-contained equipment, which is bulkier and likely to restrict passage.
• Ventilation. Assess fresh-air supply and extraction and verify their effectiveness for the hazards. Keep combustion engines and unnecessary gas cylinders outside the space and prevent exhaust or leaks entering it. Ventilation must not be presented as permission to operate a diesel engine inside a confined space.
• Testing the air. Testing may be needed to check that the air is free from toxic and flammable vapours and fit to breathe. A competent person should test using a suitable, correctly calibrated gas detector. Where the assessment shows that conditions may change, or as a further precaution, continuous monitoring of the air may be needed.
• Tools and lighting. Select equipment and its protection for the assessed atmosphere, electrical conditions and task. Equipment for a potentially explosive atmosphere must be suitable for that atmosphere; a tool described as non-sparking does not remove every ignition risk. Conductive or wet spaces need a competent electrical assessment. Neither a nominal voltage nor an RCD alone establishes that equipment is safe to use.
• Breathing apparatus. Essential if the air inside cannot be made fit to breathe because of gas, fume, vapour or lack of oxygen. Never try to sweeten the air in a confined space with oxygen, because this can greatly increase the risk of fire or explosion.
• Emergency arrangements. These must cover the necessary equipment, training and practice drills.
• Rescue equipment. Select and verify a space-specific rescue method, including suitable rated anchors, harnesses and retrieval equipment where appropriate. A line led outside, or an attendant pulling on it, is not by itself a workable rescue system.
• Communications. An adequate communication system is needed so people inside and outside the space can talk to each other, and to summon help in an emergency.
• Raising the alarm. Provide the assessed outside monitoring, alarm and rescue coordination. The attendant initiates the agreed response and must not enter impulsively; trained, equipped rescue arrangements must be ready before entry, rather than rely solely on public emergency services.

Summary notes for Element 8 · Cheat sheet · Glossary. A study aid, not published or endorsed by NEBOSH.