Ventilation of Confined Spaces

Ventilation supplies fresh air to confined spaces and removes toxic gases, fumes, and oxygen-depleted air.
Natural ventilation through openings is rarely sufficient for confined spaces used as construction workplaces.
Forced ventilation uses fans and ducting to push fresh air to the working area inside the space.
Extract ventilation removes contaminated air from the space and discharges it to a safe external location.
The ventilation rate must supply at least 6 cubic metres of fresh air per minute per person.
Duct runs must be as short and straight as possible to maintain effective airflow at the working face.
Ventilation must run continuously during the work and for a period before entry to purge the space.
Recirculating contaminated air back into the space defeats the purpose; exhaust must discharge outside.
Diesel and petrol plant inside confined spaces consume oxygen rapidly and require increased ventilation rates.
The Confined Spaces Regulations 1997 ACoP requires adequate ventilation as part of the safe system of work.

Prevent asphyxiation	Without ventilation, oxygen depletes and toxic gases accumulate in confined spaces, causing unconsciousness and death.
Fume control	Welding, painting, and engine fumes in enclosed spaces reach lethal concentrations without forced air exchange.
Legal requirement	The Confined Spaces Regulations 1997 require adequate ventilation arrangements as part of the safe system of work.

Do

Don't

Run forced ventilation to purge the space before anyone enters.
Maintain continuous ventilation throughout the entire work period inside the space.
Position supply ducting to deliver fresh air directly to the working face.
Discharge extracted contaminated air to a safe location away from entry points.
Monitor oxygen and gas levels continuously even with ventilation running.
Increase ventilation rates when diesel plant or hot works operate inside the space.
Inspect ducting for tears, disconnections, or blockages before each entry.
Size the fan and ducting to deliver adequate airflow for the space volume.
Keep duct runs short and straight to maintain airflow at the working end.
Include ventilation requirements in the confined space entry permit.

DON'T enter a confined space without running ventilation to purge it first.
DON'T switch off ventilation during breaks while workers remain inside the space.
DON'T recirculate extracted air back into the confined space.
DON'T rely on natural ventilation alone for occupied confined spaces.
DON'T position the supply duct intake near the extract exhaust discharge point.
DON'T use oxygen cylinders to ventilate a confined space; this creates fire risk.
DON'T ignore torn or disconnected ducting; it reduces airflow critically.
DON'T assume ventilation eliminates all risk; continue atmospheric monitoring.
DON'T run petrol engines inside confined spaces for ventilation or any purpose.
DON'T reduce ventilation because the fan is noisy; use quieter equipment instead.

See also: Confined Space Entry Procedures | Atmospheric Monitoring and Gas Testing

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