Cable cellars, service ducts, riser cupboards, underground utility chambers, plant rooms with limited egress — electricians routinely work in spaces that meet the legal definition of a confined space. This guide explains the Confined Spaces Regulations 1997 procedure, the electrical hazards that change the calculus, and how to plan a compliant safe system of work before anyone enters.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
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Regulation 1(2) of the Confined Spaces Regulations 1997 defines a confined space as any place that is "substantially enclosed" and where there is a reasonably foreseeable "specified risk". The definition is hazard-led, not shape-led — a small room with a flammable atmosphere is a confined space; a large but oxygen-deficient tank is a confined space.
A space is "confined" because of what could happen inside it. A walk-in basement with no ventilation and an open cable joint releasing pyrolysis fume is a confined space the moment that risk is foreseeable, even though it has a normal-size door.
For UK electricians, the spaces that most often meet the definition are: cable cellars under switchrooms, underground utility chambers and pits, service ducts and risers (depending on size and ventilation), transformer and switchgear vaults, water-storage tanks containing immersion or pump electrics, and tight plant rooms where egress is restricted by equipment or by a single small access hatch.
Riser cupboards are a judgement call. A two-metre-tall riser with normal ventilation, a standard door and no specified risk is not a confined space. A sealed riser containing battery banks with potential hydrogen build-up, or one where cable cutting will release significant fume, is.
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Regulation 4 of the Confined Spaces Regulations 1997 is explicit: no person at work shall enter a confined space to carry out work for any purpose unless it is not reasonably practicable to achieve that purpose without such entry. The legal starting position is "do not enter".
Where entry can be avoided by use of long-reach tools, fishing rods, modular cable-pulling equipment, or by re-designing the work (terminating at an accessible point, then drawing cable back), the Regulations require you to take that route. Convenience or speed is not a defence for entering when entry could reasonably have been avoided.
Where entry is necessary, Regulation 4(2) requires a safe system of work, and Regulation 5 requires adequate emergency arrangements before any person enters. HSE Approved Code of Practice L101 and HSE INDG258 set out the practical components.
HSE L101 makes clear that emergency arrangements must enable rescue without depending on the public emergency services as the primary response. By the time a fire-and-rescue team arrives, an unconscious person in an oxygen-deficient chamber is almost certainly dead. The rescue arrangement must be on-site, rehearsed, and capable of immediate action.
The Electricity at Work Regulations 1989 apply in full inside a confined space — Regulations 4, 12, 13, 14 and 16 are the load-bearing ones for the typical job. Layer these on top of the CS Regs procedure:
Section 706 (Restrictive Conductive Locations) of BS 7671 applies to many confined spaces that contain conductive surroundings. Where applicable it imposes additional restrictions on the use of mains-voltage portable equipment and on the protective measures permitted — SELV, electrical separation or reduced low-voltage become the practical options.
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A confined space RAMS is not a generic document with the words "confined space" added. It must record the actual space, the actual hazards, the actual controls and the actual rescue plan — and it must be signed off and briefed to every person involved before work starts.
Build the document in the Elec-Mate RAMS Generator — it has a confined space module that captures these fields, attaches photos of the space, and produces a PDF you can hand to the principal contractor or upload to the CDM file. The structure mirrors the HSE L101 ACOP layout, so reviewers can find what they expect to find. There is also a generic electrical RAMS template if you prefer to start from a blank.
Regulation 5 of the Confined Spaces Regulations 1997 requires "suitable and sufficient arrangements" for the rescue of any person who gets into difficulty. HSE L101 expands on what suitable and sufficient looks like. The test is not "did you have a plan?" but "would the plan have worked, on the day, with the people present?"
If a colleague collapses inside a confined space, the single biggest killer of would-be rescuers is the urge to enter and help. Unplanned entry into the same hazardous atmosphere is the most common way one fatality becomes two. The rescue plan must specify that no one enters to assist until the atmosphere is re-tested, the entrant is wearing appropriate BA, and the controller has authorised entry.
Keep the permit, the RAMS, the atmospheric test record and the briefing sheet for at least the duration of the project and as long as the duty holder requires for CDM purposes. If any near-miss or deviation occurred — a gas-detector alarm, a comms failure, an unexpected hazard — record it.
A step-by-step workflow aligned to the Confined Spaces Regulations 1997, HSE L101, INDG258 and the Electricity at Work Regulations 1989. Use it alongside a properly authored RAMS and permit to work.
Before any entry decision, work through whether the task can be done from outside — long-reach tools, withdrawing rather than terminating in-situ, CCTV inspection, remote testing, modular cable-pulling. If the work can reasonably be done without entry, Regulation 4 requires you to take that route. Record the decision in the RAMS.
Identify which of the five specified risks under the Confined Spaces Regulations 1997 are foreseeable in this space — oxygen deficiency, flammable atmosphere, harmful fume, heat, drowning or engulfment. Add the electrical hazards: live conductors near the space, induced or fault potentials, hot-work fume, battery-room hydrogen, conductive surroundings (BS 7671 Section 706).
Identify every electrical source in or adjacent to the space — incoming supply, control supplies, instrumentation, photovoltaic, generator backfeed, UPS. Isolate each, lock off with a personal padlock, and prove dead at the point of work using a tested-good GS38-compliant voltage indicator. Issue a formal permit to work covering the isolation.
Before any entry, test the atmosphere for oxygen, flammable gases and the toxic gases relevant to this space (CO, H2S, others as the risk assessment demands). Where the result is borderline or where the work itself will degrade the atmosphere, ventilate mechanically. Keep continuous monitoring throughout occupancy.
Brief every person on the safe system of work, the rescue plan, the comms arrangement and the abort criteria. Capture signatures on the permit and the briefing sheet. No one enters until the supervisor authorises entry. Top-person remains outside, in comms, with retrieval line tended.
Carry out the work under continuous atmospheric monitoring and supervisor oversight. On completion, secure isolations as needed for the next stage, re-energise under formal de-permit, file the permit and RAMS in the project record, and capture any near-miss or deviation in your reporting system.
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