Confined space incidents have a uniquely dangerous characteristic: they attract multiple fatalities. A worker collapses inside a confined space, a colleague enters to help without protection and also collapses, a third person follows — and so on. The HSE estimates that around 15 people die in confined spaces at work every year in the UK, and a significant proportion of those deaths involve would-be rescuers who entered without proper equipment.
The confined space permit to work is the document that stops this chain of events before it starts. It forces a documented confirmation that the atmosphere has been tested, that the standby person is in position, and that there is a specific rescue plan — before the first person enters.
What is a confined space?
The Confined Spaces Regulations 1997 define a confined space as any place that is substantially enclosed (though not necessarily completely enclosed) and where there is a foreseeable specified risk. The definition is broader than most people expect — it is not about physical dimensions, it is about the nature of the risk.
Common examples include:
- Manholes, sewers, and underground chambers
- Storage tanks, vessels, and silos
- Boilers, pressure vessels, and ductwork
- Open-topped pits and excavations where gases may accumulate
- Ship holds and cargo tanks
- Cellars and basements with restricted ventilation
- Loft spaces and roof voids with poor air circulation
Size does not determine whether a space is confined. A large storage tank is a confined space. A small inspection pit may not be — it depends on the risk. The question is always: is there a foreseeable risk of serious injury from the specified hazards listed in the Regulations?
The specified risks listed in the Confined Spaces Regulations include: serious injury from a fire or explosion, loss of consciousness from raised body temperature, loss of consciousness or asphyxiation from gas, fume, vapour, or lack of oxygen, drowning, and asphyxiation from a free-flowing solid.
The legal framework
| Legislation / guidance | Relevance |
|---|---|
| Confined Spaces Regulations 1997 | Duty to avoid entry; requirements for atmospheric testing, standby person, rescue arrangements, and competent persons |
| HSE INDG258 | HSE guidance on safe working in confined spaces — practical requirements for the permit system |
| BCGA CS 20 | British Compressed Gases Association guidance on confined space entry involving gas hazards |
| Health and Safety at Work Act 1974 | Overarching duty to ensure health and safety of all persons |
The Confined Spaces Regulations impose a hierarchy similar to that in other high-risk areas: avoid entry if at all possible; if entry cannot be avoided, implement a safe system of work; if a safe system cannot be implemented, only enter if the risk has been reduced to the lowest reasonably practicable level and specific conditions are met.
Atmospheric testing: the four gases
Atmospheric testing is the cornerstone of confined space safety. A multi-gas detector that measures at minimum the following four gases must be used before entry and continuously throughout the work:
| Gas / hazard | Safe limit (typical) | Risk |
|---|---|---|
| Oxygen (O₂) | 19.5% – 23.5% | Below 19.5%: oxygen deficiency — rapid unconsciousness. Above 23.5%: enrichment — dramatically increases fire and explosion risk |
| Flammable gases (LEL) | <10% LEL | Flammable gas mixtures above the Lower Explosive Limit can ignite. The atmosphere is unsafe for hot work or electrical equipment above 10% LEL |
| Carbon monoxide (CO) | <20 ppm (WEL: 20 ppm TWA) | CO is colourless and odourless — there is no sensory warning. Exposure causes headache, confusion, loss of consciousness, and death |
| Hydrogen sulphide (H₂S) | <1 ppm (WEL: 1 ppm TWA) | H₂S smells of rotten eggs at low concentrations — but the sense of smell adapts rapidly. At higher concentrations it causes immediate collapse and death |
⚠ Test at multiple levels — not just at the entry point. Heavy gases such as H₂S sink to the bottom of a confined space. Lighter gases and oxygen-deficient air may pool at the top. Test at the top, middle, and bottom of the space before entry, and lower the detector to the working level on a rope before the first person enters.
Continuous monitoring during entry
A single pre-entry test is not sufficient. Atmospheric conditions in confined spaces can change rapidly — a vehicle running nearby, a chemical reaction in a sewer, a disturbed sediment releasing gases. Each entrant must carry a personal gas monitor with an audible alarm, set to alert at the appropriate action levels. The permit must confirm that continuous monitoring is in place and that the alarm action levels have been set and briefed.
The standby person: duties and constraints
The Confined Spaces Regulations require that where a person enters a confined space, a suitable person is stationed outside — the standby person. The standby person's role and constraints are specific and must be recorded on the permit.
What the standby person must do
- Maintain continuous communication with the entrant(s) throughout the operation
- Monitor the atmospheric readings from outside the space
- Raise the alarm if the entrant fails to respond or signals distress
- Initiate the rescue plan without entering the space themselves
- Keep a record of entry times and exit times for every entrant
⚠ The standby person must not enter the confined space under any circumstances — including to attempt a rescue. This is the rule that saves multiple lives when things go wrong. The standby person's job is to activate the rescue plan from outside. A standby person who enters to rescue an incapacitated colleague will almost certainly become a second casualty.
The standby person cannot be shared
If two separate confined spaces are in use simultaneously, each requires its own dedicated standby person. A standby person cannot cover multiple entry points — their attention cannot be divided.
The rescue plan
The Confined Spaces Regulations require that suitable arrangements for rescue are in place before entry begins. The rescue plan must be written, specific, and executable without entering the confined space. It must cover:
- Non-entry rescue method: How will the entrant be extracted without anyone entering the space? This typically means a rescue tripod and lifting system with a harness worn by the entrant from the moment they enter. The rescue line must be attached before entry.
- Communication method: How will the standby person communicate with the entrant, and what signals mean "exit now"?
- Emergency contact: Who is called if non-entry rescue fails? The local fire service specialist rescue team, or the employer's own specialist rescue team, must be identified by name and number.
- First aid: What first aid will be provided after recovery? A person extracted from an oxygen-deficient atmosphere needs supplemental oxygen immediately — this must be available on site.
Ventilation
Forced ventilation is used to dilute atmospheric hazards and maintain safe oxygen levels during entry. The permit must confirm that ventilation is operational before the first person enters and that it remains running throughout the work. Key points:
- Natural ventilation is rarely sufficient — forced ventilation (a powered fan unit) is almost always required
- The ventilation supply must introduce fresh air, not recirculate air from within the space
- Exhaust air from the space must be directed away from the entry point and from the standby person's position
- Work must be suspended if ventilation fails — the space must be re-tested before re-entry
What a confined space permit must include
Confined Space Pre-Authorisation Checks
- Atmospheric test results recorded — O₂, LEL, CO, and H₂S all within safe limits
- Continuous gas monitor active on each entrant with audible alarm set at action levels
- Standby person in position at entry point — confirmed will not enter under any circumstances
- Rescue equipment ready and accessible — tripod, lifeline, and rescue harness in place
- Communication between entrant and standby confirmed and tested
- Forced ventilation confirmed operational before first entry
Common mistakes to avoid
- Testing only at the entry point. Gas stratifies by density. Test at the top, middle, and bottom of the space — and then lower the detector to the working level before entry.
- No rescue harness worn during entry. If the entrant is not wearing a rescue harness with a lifeline attached to a tripod before they enter, non-entry rescue is not possible. The harness must be on before the first step into the space.
- Standby person who "also" has other duties. The standby person's sole duty during the operation is to monitor the entrant and be ready to activate the rescue plan. They cannot also be taking deliveries, answering phones, or supervising other work.
- Using a single-gas detector. Many confined space incidents involve a combination of hazards — oxygen deficiency and toxic gas simultaneously. A single-gas CO detector will not detect H₂S or an oxygen-deficient atmosphere. A four-gas (minimum) detector is required.
- Ventilation turned off "briefly" during the work. Ventilation must run continuously. A brief interruption is sufficient for hazardous gas to accumulate to dangerous levels before the monitor alarm sounds.
- Treating a completed pre-entry test as covering the whole shift. If work is interrupted and the space is left unattended, atmospheric conditions can change significantly. The space must be re-tested before anyone re-enters after any break.
Download a free confined space permit template
We've produced a free Confined Space Entry Permit to Work template in Word (.docx) format, available in both a pre-filled version (standard hazards and controls already populated) and a blank version.
Confined Space Entry Permit to Work — Free Template
Covers the Confined Spaces Regulations 1997 and HSE INDG258. Pre-filled with standard atmospheric testing checks, standby person requirements, and rescue plan fields. Editable Word (.docx) format.
For all permit types, visit the templates page.
Beyond paper: managing confined space permits digitally
Confined space incidents often involve a failure to follow a step that was not clearly recorded as a requirement. Paper permits can be filled in retrospectively, skipped under time pressure, or lost after the event. PermitDesk generates confined space permits digitally — with the atmospheric test results recorded as specific readings against pass/fail thresholds, the standby person's acknowledgement captured as a named digital signature, and a full timestamped audit trail automatically stored.
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PermitDesk enforces every required step. Nothing is authorised until every check is confirmed. Full audit trail included.
Start your free 14-day trialRelated reading
→ What is a permit to work? A plain-English guide
→ Electrical Isolation Permits: lock-out tag-out & confirmed dead procedure
→ Working at Height Permits: WAH Regs 2005, rescue plans & harness inspection
→ Excavation & Ground Works Permits: CDM 2015 & service strikes
→ Lifting Operations Permits: LOLER 1998 & Appointed Person duties