Confined Space Entry Safe System of Work: A Practical Guide for UK Contractors

Confined space entry is one of the higher-risk activities a contractor can undertake, and the law is explicit about what you must put in place before anyone goes in. The Confined Spaces Regulations 1997 require a safe system of work for every entry — and getting it wrong can be fatal. This guide explains what that system must contain and how to build one that actually protects your workers.

What Counts as a Confined Space?

Under the Confined Spaces Regulations 1997, a confined space is any place that is substantially enclosed and where there is a reasonably foreseeable specified risk. That includes:

• Manholes, sewers and inspection chambers
• Storage tanks, silos and vats
• Ducts, culverts and tunnels
• Excavations deeper than around 1.2 m where risks are present
• Roof voids, cellars and similar enclosed areas

The specified risks listed in the Regulations include loss of oxygen, presence of flammable or toxic gases, liquids or free-flowing solids that could engulf a person, and excessive heat.

The First Principle: Avoid Entry if Possible

The Regulations set a clear hierarchy. The first question is always: can the work be done without entering the confined space? Remote cameras, extended-reach tools, robotic inspection equipment and external cleaning systems can all eliminate the need for entry. Only when avoidance is genuinely impracticable should you move to planning a safe system of entry.

What the Safe System of Work Must Cover

Once entry is confirmed as necessary, you need a documented safe system of work. This is built on a suitable and sufficient risk assessment (required by regulation 3 of the Management of Health and Safety at Work Regulations 1999) and a method statement — together forming the RAMS document. The safe system must address each element below.

1. Appointment of a Competent Supervisor

Someone must be in charge who understands the risks and controls. This person does not necessarily enter the space but oversees the operation, controls permits, and has authority to stop work.

2. Atmospheric Testing

Test the atmosphere before entry and continuously during work where practicable. Use a calibrated multi-gas detector to check for:

• Oxygen levels (safe range: 19.5%–23.5%)
• Flammable gases (LEL monitoring)
• Toxic gases relevant to the space — hydrogen sulphide (H₂S) in sewers, carbon monoxide in combustion environments, and so on

Never rely on smell or sight to judge atmosphere quality.

3. Isolation and Purging

Isolate all mechanical, electrical, hydraulic and pneumatic services before entry. In pipework or vessels, use physical isolation (blank flanges, spades) rather than valves alone. Purge or ventilate the space and confirm the atmosphere is safe before entry begins.

4. Ventilation

Natural ventilation may be sufficient in some spaces; most require forced ventilation using explosion-proof fans and ducting. Ventilation must be maintained throughout the work, not just used to clear the space before entry.

5. Provision of Suitable Equipment

Equipment for confined space work includes:

Breathing apparatus may be required from the outset in atmospheres that are or may become immediately dangerous to life or health (IDLH conditions).

6. Permit to Work

For confined spaces, a formal permit-to-work system is best practice and is effectively required wherever the risks are significant. The permit records: what the space is, what testing has been done, what controls are in place, who has authorised entry, time limits, and what happens in an emergency. It is signed on and signed off at the end of each shift.

7. Attendant Outside the Space

At least one trained attendant must remain outside the confined space at all times during entry. Their role is to maintain communication, monitor conditions, operate emergency retrieval equipment, and raise the alarm — not to enter the space themselves in an emergency.

8. Emergency and Rescue Arrangements

This is where confined space accidents turn fatal. Rescuers who enter without proper equipment and training frequently become casualties themselves. Your safe system must specify:

• Non-entry retrieval first: harness, lifeline and tripod/davit arm to haul an incapacitated worker out without entry
• When entry rescue is unavoidable, trained confined space rescue operatives with appropriate breathing apparatus
• Arrangements for emergency services — have the site address, access details and space type ready to communicate immediately

The rescue plan must be in place before entry begins, not improvised after something goes wrong.

Competence and Training

The Confined Spaces Regulations 1997 require that anyone who enters a confined space, supervises entry, or carries out rescue is competent to do so. Competence typically means formal training (such as that provided to the IATP or Lantra syllabus standards) combined with practical experience. Refresher training and drill exercises keep skills current.

Substances Inside the Space

Where hazardous substances are present — residues, gases generated by work activities, or materials being applied — the Control of Substances Hazardous to Health Regulations 2002 (COSHH) assessment must be integrated into the confined space risk assessment. Respiratory exposure limits do not disappear because you are underground.

Pulling It Together

A confined space entry safe system of work is not a single document — it is a coordinated set of controls, equipment, trained people and emergency arrangements that must all be in place simultaneously. The RAMS documentation records the thinking; the permit to work controls each specific entry; and the trained team executes and monitors the controls in real time. Miss any element and the system fails.