Carbon monoxide is odourless, colourless and produced by every combustion engine, including the generator on a welfare unit. Workers die from it in the UK most years, almost always the same way: an engine running in or too close to an enclosed space. The law here is the general duties of the 1974 Act and the risk assessment requirement of MHSWR, but the controls are so well established that HSE treats failures as basic.
The non-negotiables
- Exhaust to open air, always. Welfare units are designed for outdoor siting with exhausts venting externally; a unit must never be placed inside a building, container or excavation, and nothing may enclose it after siting, scaffolding and hoarding creep is how open-air becomes enclosed by accident
- Vents stay clear. The louvres and exhaust outlets exist to move air; the "do not obstruct vent" stickers are load-bearing, not decorative
- Detection as backup, not substitute: our units carry a carbon monoxide sensor in the cabin, it is the last line, not the plan
- Refuelling discipline: engine off and cooled, covered in the handover pack and our risk assessments
Why demand-managed generators help
Ecosmart management means the generator runs only when there is electrical demand, fewer running hours per week is less fuel, less noise, and less exhaust produced in the first place, the control hierarchy’s favourite kind of control: less hazard, not just managed hazard. Our generator vs mains guide covers the wider power question.
Your site assessment’s job
Confirm the siting position is genuinely open-air and will stay that way through the programme, keep the exhaust side clear of doorways, windows and work positions, and induct the crew that the generator bay is not a drying cupboard. Ten minutes in the site risk assessment, permanently cheap against the alternative.
Plain-English summary, not legal advice. HSE guidance on CO and engine exhaust is at hse.gov.uk.