174 (1) If a hazardous substance may be produced in a confined space by the work to be performed,
(a) the confined space must be ventilated in accordance with subsection (2); or
(b) each person granted access to the confined space must use a respiratory protective device or breathing apparatus referred to in section 142.
(2) If an airborne hazardous substance or oxygen in the atmosphere in a confined space is maintained at the value, level or percentage referred to in subsection 171(2) by the use of ventilation equipment, a person may only be granted access to the confined space if
(a) the ventilation equipment is
(i) equipped with an alarm that will, if the equipment fails, be activated automatically and be audible or visible to any person in the confined space, or
(ii) monitored by an employee who is in constant attendance at the equipment and in communication with any person in the confined space; and
(b) in the event of failure of the ventilation equipment, sufficient time will be available for the person to escape from the confined space before one of the following occurs:
(i) their exposure to or the concentration of a hazardous substance in the confined space is more than the value, level or percentage prescribed in paragraph 171(2)(a) or (b), and
(ii) the percentage of oxygen in the atmosphere ceases to meet the requirements of paragraph 171(2)(c).
(3) The employee referred to in subparagraph (2)(a)(ii) must activate an alarm in the event of faulty operation of the ventilation equipment.
