Tanks, silos, sewers, ducts and pits are among the most dangerous environments in any UK workplace. The risk is rarely visible: it's the atmosphere, the restricted exit and the instinct to rush in after a colleague. This guide explains the dangers and the safe system of work the law requires.
Why confined spaces are so deadly
A confined space is any substantially enclosed space where serious injury can result from hazardous conditions — toxic gas, oxygen deficiency, flammable atmospheres or engulfment. The harm is usually invisible and rapid.
The HSE repeatedly highlights that many confined-space deaths are would-be rescuers entering without protection. Planning is everything.
The four things that catch people out
Most incidents come down to a few factors. Tap each to see what to control.
The invisible killer
Toxic gas, too little oxygen or a flammable build-up. You often can't see or smell it — test before and during entry.
The main atmospheric dangers
The biggest killers are in the air itself. Respect these three.
Toxic atmosphere
Hydrogen sulphide, carbon monoxide and other gases can overcome you in seconds.
Oxygen issues
Low oxygen causes collapse without warning; excess oxygen makes fire far more likely.
Engulfment & fire
Free-flowing solids or liquids can bury you; flammable vapours can ignite in an instant.
Never enter to rescue without training and equipment. Unprepared, the space will likely claim you too.
The safe system of work
Confined-space safety is a sequence — get one step wrong and the rest can't save you:
Avoid entry if you can
Can the task be done from outside? The safest confined-space entry is the one you don't make.
Assess, isolate, test
Risk-assess, lock off all inflows, and test the atmosphere before and throughout entry.
Permit & equip
Work to a permit, with the right RPE, gas monitor, lighting and communications.
Have rescue ready
A trained, equipped rescue team and plan must be in place — never rely on improvised rescue.
What the law requires
Under the Confined Spaces Regulations 1997 (enforced by the HSE), employers must avoid entry where reasonably practicable, use a safe system of work, and have suitable emergency arrangements. In practice:
- Avoid entry into confined spaces where reasonably practicable
- Carry out a suitable risk assessment
- Follow a safe system of work, usually a permit
- Put suitable emergency and rescue arrangements in place