Confined spaces are one of the most misunderstood hazards on UK sites. Workers assume a space is only "confined" if it's tiny or underground — but a partially enclosed plant room, a large duct, an unventilated riser or even an open-topped tank can all count. And when things go wrong in a confined space, they go wrong fast: the biggest killer isn't the fall or the fire, it's the atmosphere. Worse still, around two-thirds of confined space fatalities are the people who go in to attempt a rescue.
If your work touches drainage, groundworks, tanks, vessels, ductwork, risers, boilers or deep excavations, this one matters. Here's what a confined space risk assessment needs to cover, when the Confined Spaces Regulations 1997 apply, and how to get the paperwork straight.
What counts as a confined space?
Under the Confined Spaces Regulations 1997, a confined space is any place that is substantially (though not always entirely) enclosed and where there's a reasonably foreseeable risk of a "specified" hazard. Both parts have to be true.
The specified risks are:
- Serious injury from fire or explosion
- Loss of consciousness from raised body temperature
- Loss of consciousness or asphyxiation from gas, fume, vapour or lack of oxygen
- Drowning from a rise in liquid level
- Asphyxiation from a free-flowing solid (grain, sand, flour) or being trapped by one
So a big, well-ventilated room isn't a confined space just because it's enclosed. But a small unventilated meter cupboard where solvent vapour could build up absolutely is. Common examples on construction and M&E jobs include:
- Manholes, sewers, drainage chambers and inspection pits
- Storage tanks, vessels and silos
- Ductwork, flues and unventilated plant rooms
- Deep or poorly ventilated excavations and trenches
- Service risers and voids
- Boilers and combustion chambers
If you're not sure whether a space qualifies, treat it as one until your assessment proves otherwise.
The golden rule: avoid entry if you can
The first duty under the regulations is not to work in a confined space at all if the job can be done another way. Before you plan entry, ask:
- Can the task be done from outside — with a camera, a long tool, remote monitoring or by draining/cleaning the space first?
- Can equipment be modified so entry isn't needed for future maintenance?
Only when entry genuinely can't be avoided do you move on to a safe system of work. This is the same hierarchy-of-control thinking you'll recognise from any risk assessment — eliminate first, then control.
What a confined space risk assessment must cover
A suitable and sufficient assessment goes well beyond a generic hazard list. It should identify the specific space, the task, and the controls that make entry safe. Cover at least:
1. The space and the task — location, dimensions, access/egress points, and exactly what work is being done inside.
2. The hazards — atmospheric (oxygen deficiency or enrichment, toxic/flammable gases), physical (engulfment, moving parts, heat), and residues from previous contents.
3. Atmospheric testing — what gases you'll test for, with a calibrated multi-gas monitor, before and continuously during entry.
4. Ventilation and purging — mechanical ventilation where needed to keep the atmosphere safe.
5. Isolation — locking off pipes, electrical supplies and moving plant so nothing can start or flow into the space.
6. Access equipment — tripods, winches, harnesses and lifelines for entry and recovery.
7. Communication — how the person inside stays in contact with the person outside.
8. Emergency and rescue arrangements — this is the part people skip, and it's the part that kills. You need a rescue plan that does not rely on someone rushing in unprotected.
9. Competence and training — everyone involved must be trained and, for higher-risk spaces, hold the appropriate confined space qualification.
Because the controls are detailed and sequential, confined space work almost always needs a method statement alongside the risk assessment — a combined RAMS document that spells out the safe system of work step by step.
Permits and rescue: the two things people get wrong
Permit to work
For most medium- and high-risk confined space entries, a permit-to-work system is the practical way to control it. The permit confirms that testing has been done, isolations are in place, rescue arrangements are ready and the space is safe to enter — and it hands responsibility to a named person. It's a formal check that stops entry happening on autopilot. If you're new to the concept, our guide on what a permit to work is walks through the main types, including confined space entry permits.
Rescue arrangements
Rescue is where confined space incidents multiply. A plan that amounts to "someone will pull them out" or "we'll call 999" is not a plan. Standard fire-and-rescue crews may not arrive equipped or in time. Your arrangements must be suitable and immediately available, and they must protect the rescuer as well as the casualty. That typically means recovery equipment (tripod and winch), breathing apparatus where the atmosphere may be dangerous, trained rescuers on standby, and resuscitation equipment.
A quick pre-entry checklist
Before anyone goes in, confirm:
- [ ] Entry can't reasonably be avoided
- [ ] A confined space risk assessment and safe system of work are in place
- [ ] Permit issued and signed by an authorised person
- [ ] Space isolated (mechanical, electrical, process)
- [ ] Atmosphere tested with a calibrated monitor — and monitoring continues during work
- [ ] Ventilation running where required
- [ ] Access, lighting and communication sorted
- [ ] Rescue equipment on site and a trained standby person in position
- [ ] Everyone briefed — a short toolbox talk is a good way to record it
FAQ
Is a confined space entry always a legal requirement to have a permit?
No — the Confined Spaces Regulations 1997 don't mandate a permit in every case, but they require a safe system of work. For anything beyond the lowest-risk entries, a permit-to-work is the recognised way to demonstrate that system is being followed.
Who can carry out a confined space risk assessment?
A competent person — someone with the training, knowledge and experience to identify the specific and atmospheric hazards involved. A template gives you a proper structure, but a competent person still has to complete and sign it off for your actual space.
Does an excavation count as a confined space?
It can. A deep or poorly ventilated trench where gases could accumulate, or where there's a risk of engulfment, may fall under the regulations. Shallow, open, well-ventilated excavations usually won't — but assess each one on its facts.
Can I use a generic template for any confined space?
A template is your starting framework, not the finished job. You edit it to reflect the specific space, task, atmosphere and rescue plan. A blank generic form signed without thought helps nobody.
Get the paperwork sorted
Confined space work is high-consequence, so the documentation needs to be right. Start with the editable templates in our RAMS & Permits Bundle, which covers method statements and permit-to-work forms for high-risk activities. Groundworkers doing drainage, chambers and deep excavations will find confined space, permit-to-dig and related documents grouped in the Groundworker Risk Assessment Pack. And if you want every risk assessment, permit and monitoring form under one roof — updated as legislation changes — SafetyPod Membership gives you unlimited access for £69/year. Written by a NEBOSH-qualified team, editable, and downloaded the moment you check out.