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Part 9 Confined Spaces
Ventilation
9.30 Continuous ventilation
Every confined space must be ventilated continuously while a worker is inside the space, except in
(a) an atmosphere intentionally inerted in accordance with section 9.29,
(b) a low hazard atmosphere controlled in accordance with section 9.31(2), or
(c) an emergency rescue, if ventilation is not practicable.
9.31 Low hazard atmospheres
(1) The employer must ensure that a minimum of 85 m3/hr (50 cfm) of clean respirable air is supplied for each worker inside a confined space with a low hazard atmosphere, except as permitted in subsection (2).
(2) Continuous ventilation is not required in a confined space which has a low hazard atmosphere, if
(a) the atmosphere is continuously monitored and shown to contain clean respirable air, and
(b) the space has an internal volume greater than 1.8 m3 (64 cu ft) per occupant, is occupied for less than 15 minutes, and the work inside the space generates no contaminants other than exhaled air.
9.32 Mechanical ventilation
(1) A ventilation system for the control of airborne contaminants in a confined space must be designed, installed and maintained in accordance with established engineering principles and must be specified in the written procedures.
(2) Ventilation equipment must be located and arranged so as to adequately ventilate every occupied area inside the confined space.
(3) If a contaminant is produced in a confined space, it must be controlled at the source by a local exhaust ventilation system if practicable, by general (dilution) ventilation, or by a combination of both.
(4) If practicable, a mechanical ventilation system for a confined space must be sufficient to maintain concentrations of airborne contaminants below the applicable exposure limits.
9.33 Natural ventilation
(1) If natural ventilation is relied upon for the control of airborne contaminants in a confined space, the rate of airflow through the space must be monitored and must be sufficient to maintain concentrations of airborne contaminants below the applicable exposure limits.
(2) Natural ventilation must not be used
(a) to ventilate a confined space that has a high hazard atmosphere, or
(b) if such ventilation could draw air other than clean respirable air into the confined space.
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