Tanks, silos, manholes, ducts, pits — confined spaces are everywhere, and they're among the most lethal environments in any workplace. The danger is rarely visible: it's the atmosphere, the restricted exit and the temptation to rush in after a colleague. This guide explains the risks and the system that keeps people alive.
Why confined spaces are so deadly
A confined space is any largely enclosed space where serious injury can occur from hazardous conditions — not just tight spaces, but anywhere dangerous gases, fumes or low oxygen can collect. The harm is usually invisible and fast.
Worse still, a high proportion of confined-space fatalities are would-be rescuers who rushed in without protection. That's why planning matters more here than almost anywhere.
The four things that catch people out
Most confined-space 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. These three are the ones to respect.
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. If you go in unprepared, the space will likely claim you too.
The safe system of work
Confined-space safety is a sequence — get any 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 HSA expects
Under the Safety, Health and Welfare at Work (Confined Spaces) Regulations 2001employers must avoid confined-space entry where they can, assess the risk and put a safe system and rescue plan in place. 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