Confined space ventilation: what’s required before and during entry. 

A safe atmosphere must be established before anyone enters a confined space and maintained while it is occupied. Equipment selection starts with the risk assessment, including oxygen levels, airborne contaminants and whether there is a risk of fire or explosion. Depending on the application, ventilation may involve a Venturi Air Mover, purging fan or portable blower extractor. What you can never use for purging or ventilation is oxygen.

Overview. 

• A safe oxygen level is 19.5% to 23.5% by volume, and the gas mixture used for ventilation or purging must not exceed 21% oxygen. 

• Purging and ventilating are two different jobs. Purging displaces the contaminant; ventilation supplies breathable air. 

• A safe atmosphere must be maintained throughout occupancy.

• Ventilation never replaces atmospheric testing. You cannot detect an unsafe atmosphere by smell or feel. 

• Equipment selection depends on the atmosphere, contaminants and ventilation requirements.

A space doesn’t have to be small to be confined. 

The term covers any enclosed or partially enclosed space that wasn’t designed to be occupied by people, is entered to carry out work, and carries a risk from its atmosphere. Tanks, silos, pits, vats, tunnels, pipes, ducts and sealed plant rooms all qualify. Size isn’t the test, and neither is how easy the space is to get into. 

What makes them dangerous is that the atmosphere changes on its own. Oxygen gets consumed by rust forming inside a steel tank, absorbed by grain or wood chips in a sealed silo, displaced by gases from biological processes, or used up during combustion. None of that is visible from the hatch.

What the regulations require. 

Safe Work Australia’s model Code of Practice: Confined spaces sets out how to meet the WHS Regulations, and each state adopts its own version, such as the SafeWork NSW code or the WorkSafe Queensland code. The atmosphere must have a safe level of oxygen, and where that isn’t reasonably practicable, anyone entering a space below 19.5% oxygen must be given air-supplied respiratory equipment. Purging or ventilating contaminants must be carried out so far as is reasonably practicable, and the gas mixture used must not exceed 21% oxygen by volume. 

Air normally contains 21% oxygen, with 19.5% to 23.5% considered a safe oxygen range. Oxygen must never be used to purge or ventilate a confined space, as the gas mixture used cannot exceed 21% oxygen. A competent person must also complete and record the risk assessment before work begins. Safe Work Australia’s Model Code of Practice: Confined spaces provides the national model guidance, although requirements should also be checked with the relevant state or territory regulator.

Purging and ventilating are two different jobs. 

Purging displaces contaminant from the space, often using an inert gas such as nitrogen to clear flammable vapours. The problem is what that does to the oxygen. Purging with an inert gas displaces the air along with the contaminant, leaving an oxygen-deficient atmosphere and the risk of asphyxiation. 

Purging with an inert gas can leave the space oxygen deficient, so a safe atmosphere must be established and verified before entry. Ventilation may then use local exhaust where contaminants come from a specific point, or dilution ventilation where they are more widely dispersed. Atmospheric testing is still required before entry. Safe Work Australia’s confined spaces guidance explains these requirements in more detail

Choosing the equipment. 

Equipment selection starts with the risk assessment. The atmosphere is a key consideration, particularly where flammable gases, vapours or combustible dust may be present. The contaminant, required airflow and space configuration also affect the ventilation setup. Safe Work Australia

These options aren’t interchangeable. Venturi Air Movers use compressed air, while other portable ventilation equipment may use electrical power. Selection depends on the atmosphere, airflow requirement and application. Fanquip’s confined-space ventilation guide explains where Venturi Air Movers, purging fans and portable ventilation equipment fit.

Ventilation doesn’t replace testing. 

The senses are no guide to whether the air in a confined space is safe, since many toxic and flammable gases, and unsafe oxygen levels, can’t be detected that way. Testing happens before entry and monitoring continues during it. 

Where you test matters as much as when. Gases stratify inside the space, and lighter gases can vent into the breathing zone of the person doing the testing, so remote regions and different levels need checking rather than one reading at the access point. Whether re-testing or continuous monitoring is required comes out of the risk assessment, which is why the assessment drives the ventilation plan rather than the other way around. 

Getting the setup right. 

Placement decides how well the ventilation performs. How far the ducting needs to run, how far apart the supply and exhaust sit, and where the discharge points all depend on the shape of the space, the contaminant and where the work is happening. Two tanks of the same volume can need different setups. 

Getting the setup right depends on the space, contaminant and work being carried out. Fanquip offers Venturi Air Movers, purging fans and portable blower extractors for confined-space ventilation applications. Talk to the Fanquip team about the requirements for your application. Fanquip

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