Ventilation of Confined Spaces

Ventilation in confined spaces replaces contaminated air with fresh air, reducing the concentration of toxic gases and increasing oxygen.
Natural ventilation through openings is rarely adequate for confined spaces — forced mechanical ventilation is almost always required.
Forced fresh air must be delivered to the working position inside the space, not just blown towards the entrance.
The ventilation system must run continuously before, during, and after the entry until the last person has left the space.
Air must be drawn from a clean source — positioning the fan inlet near exhaust fumes, generators, or chemical stores is dangerous.
The ventilation rate must be sufficient to dilute and remove contaminants at the rate they are being generated inside the space.
Flexible ducting directs air to the bottom or far end of the space where gases accumulate and fresh air does not reach naturally.
Ventilation does not replace atmospheric monitoring — gas testing must continue even with ventilation running throughout the entry.
Petrol or diesel-powered equipment must never be used inside a confined space — the exhaust fumes are lethal in enclosed areas.
The ventilation equipment must be inspected and tested before use, with backup available in case of primary fan failure.

Replace toxic air	Ventilation removes hydrogen sulphide, methane, and other lethal gases — without it, the atmosphere can kill within seconds.
Oxygen supply	Ventilation maintains breathable oxygen levels in spaces where oxidation, biological activity, or gas displacement reduces oxygen.
Continuous operation	Stopping ventilation even briefly allows toxic gases to rebuild to dangerous levels — it must run throughout the entire entry.

Do

Don't

Provide forced mechanical ventilation for all confined space entries requiring it.
Position the fan intake in clean air, away from exhausts, generators, and chemical stores.
Direct flexible ducting to the lowest or furthest point inside the confined space.
Start ventilation before entry and run it continuously until the last person exits.
Ensure the ventilation rate is adequate to dilute contaminants generated during work.
Continue atmospheric monitoring even with ventilation running throughout the entry.
Test and inspect ventilation equipment before every confined space entry.
Have backup ventilation available in case the primary fan fails during the entry.
Use only electric or pneumatic equipment inside the space — never petrol or diesel.
Record ventilation arrangements and air quality readings on the entry permit.

DON'T rely on natural ventilation alone for confined space entries.
DON'T draw fresh air from near exhausts, generators, or chemical storage areas.
DON'T point the duct at the entrance — direct it to where contaminants accumulate.
DON'T stop ventilation while anyone is inside the confined space.
DON'T assume one fan size fits all spaces — match the ventilation rate to the hazard.
DON'T stop gas monitoring because ventilation is running — conditions can still change.
DON'T use untested or faulty ventilation equipment for confined space entries.
DON'T enter without a backup plan if the primary ventilation system fails.
DON'T use petrol or diesel engines inside any confined space — their fumes kill.
DON'T leave ventilation details off the entry permit — they are a critical control.

See also: Confined Space Awareness | Atmospheric Monitoring and Gas Testing

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