A confined space doesn't have to be tight or cramped — it just has to be enclosed enough for dangerous air to build up. Tanks, pits, manholes, silos: this guide keeps it simple, covering why they're so dangerous and the steps that keep everyone out of trouble.
What makes them so dangerous
The threat in a confined space is usually the air — toxic gas, too little oxygen, or a flammable build-up. None of it is obvious, and it can act in seconds.
And tragically, a lot of those who die are people who climbed in to save a workmate. Planning beats bravery every time.
The things that catch people out
A few factors cause most incidents. Tap each to see what to keep on top of.
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 big air dangers
The air itself is the main killer. 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 go in to rescue without training and kit. Unprepared rescuers become victims.
The safe steps
Get the order right and the space stays survivable:
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 says
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