Confined space ventilation:

The purpose of ventilation in a confined space is to control fumes, dust, vapours, mists and other corrosive or toxic materials to a concentration below the permissible exposure limit (PEL).

Within the space, you must maintain a consistent oxygen level greater than 19.5% but less than 23% O2 by volume.

The difference between purging and ventilating a confined space:

Purging involves removing contaminants inside the confined space by displacing air to achieve acceptable atmospheric levels.

For example, a confined space could contain toxic gas. If you blew air into the space, you would reduce the gas concentration below the appropriate atmospheric exposure level.

Once you have removed (purged) the contaminants, you can ventilate the confined space.

Ventilating involves bringing continuous fresh air into the space by mechanical means to maintain acceptable atmospheric levels.

You must have continuous ventilation for the entire time employees are working in the space. Along with maintaining a safe oxygen level, ventilation:

  • provides protection in case chemicals are accidentally released
  • removes contaminants produced from work in the space, and
  • cools down the confined space.

Continuous ventilation is preferred to using personal respiratory devices.

Once you have purged, ventilated and stabilized the atmosphere, there should be continuous monitoring from an outside space for the duration of the entry. Entrants wearing personal monitoring devices or using suitable area monitors may also monitor the atmosphere from within the space.

confined space approximate purge times

What is inerting?

Inerting is a special form of purging and ventilating. Inerting involves purging oxygen from a confined space using an inert gas like nitrogen, carbon dioxide or argon. This is done to remove a fire or explosion hazard.

Inerting the confined space decreases the oxygen concentration below the level that supports combustion. Since the confined space is oxygen-deficient, workers entering must use appropriate supplied-air respirators.

There are two options for ventilating a confined space:

  1. Forced-air ventilation: Uses fresh, forced-air to ventilate a confined space by displacing and diluting air.
  2. Exhaust ventilation: Uses an exhaust to continuously removing contaminants at the source point.

Axial fan versus centrifugal blower:

When selecting a fan or blower, all ventilators have two characteristics:

  1. Air flow – Air volume delivered and measured by cubic feet per minute (CFM).
  2. Air pressure – Force of air volume is measured by inch of water gauge (WG).

Air Systems Model SVF-8AC Steel Axial Fans
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Axial fans:

An axial fan creates high airflow but the blade design develops lower pressure. When used with ducting, the ventilation duct creates air movement resistance and the axial fan becomes inefficient at longer distances. Axial fans are designed with several large paddle blades to create a large volume of airflow.

When to use an axial fan:
Axial fans are lightweight, low cost and best when working at short distances with minimal ducting, preferably 15 to 25 feet of flexible ducting.

Air Systems 8” Centrifugal Blower for Non-Hazardous Locations
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Centrifugal blowers:

A centrifugal blower uses a “squirrel cage” designed with numerous forward curving blades on a circular wheel. The blades create significant volume (CFM) and very high air pressure (WG).

When to use a centrifugal blower:
Centrifugal blowers are typically heavier and cost more than axial fans due to the motor required to efficiently run the blades.

Centrifugal blowers are used to move air long distances using long or multiple lengths of duct.

Air Systems Inline Axial Fans
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In-line axial fans

The in-line axial fan can be used by itself or with a fan or blower as a velocity accelerator for long duct distances over the 15 or 25-foot standard duct length.

When to use an in-line axial fan:
When ventilating at long distances, add an in-line fan to the ducting to increase or maintain airflow for long distances. In-line fans can be used with either axial or centrifugal blowers to extend longer ventilation distances.

Special application ventilators:

Air Systems venturi air blower
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Venturi air blower:

The Venturi air blower operates with a pneumatic air hose and uses no moving parts or blades. A hollow hub spins air, similar to a jet engine, to create a tremendous amount of airflow.

When to use a Venturi air blower:
With no mechanical blade, the Venturi is not specifically designed to force air through flexible ducting.

The Venturi is primarily used as a suction or push device used on a tank and can be used in conjunction with an axial or centrifugal fan to rapidly remove gases from a tank. Venturi bases are designed to fit American Petroleum Institute (API) standard tanks.

The dos and do nots of ventilation:


  • Follow all manufactures guidelines, and provincial/federal regulations.
  • Retrieve fresh air source away from contaminants (i.e. tailpipe exhaust).
  • Set blower a minimum of 5 feet back from opening.
  • Keep ventilation hose as straight as possible.

Do not:

  • Have unnecessary bends in ventilation hose.
  • Place intake downwind from exhausting air.
  • Allow air to short circuit in the confined space.
  • Allow air to recirculate. Keep fresh air intake supply away from exhaust expelling zone.

How Levitt-Safety can help:

Our team at Levitt-Safety has expert knowledge on legal requirements and best practices. We can provide advice for the best ventilation options for any type of confined space.

If you’d like to chat more or get a quote on multiple pieces of equipment, fill out the form on this page and a member of our team will contact you.

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