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Forced Air Ventilation

This alternate procedure may only be used if an actual or potential atmospheric hazard is the only hazard within the space.

General Requirements

Entry procedure

  1. The entry supervisor must complete the Assessment Form prior to personnel entering the confined space, including atmospheric testing.
    • Initial atmospheric testing readings shall be documented on the form (i.e. prior to mechanical ventilation efforts).
    • Efforts to determine the source of the adverse atmospheric readings should be made and the source eliminated if at all possible.
  2. Ventilate the space for a minimum of 30 minutes, up to 60 minutes, and test again. Ventilation of the space is determined by:
    • The size and configuration of the confined space;
    • The size of the entrance into the space;
    • The gas(es) present within the space and amount; and
    • The source of make-up air.
  3. If the atmosphere has reached acceptable levels (as indicated by testing) with ventilation, document the readings on the form.
    • Check the second box on the form under "For the purposes of this entry (check one of the boxes below)," which indicates the alternate ventilation procedure will be implemented for entry.
    • Entry Supervisor must sign at the bottom of the form to indicated entry is permitted/approved under these conditions.
  4. Continuous mechanical/forced air ventilation must be provided as long as entrants are in the space.
    • Ventilation equipment (forced air and/or exhaust) should be directed to the immediate vicinity of each entrant within the confined space.
  5. Continuous atmospheric monitoring/testing is required during the entire entry. 
    • Atmospheric testing readings shall be documented on the form at least hourly.
    • If mechanical ventilation equipment should fail during entry operations, all employees must immediately evacuate the space until equipment is restored/replaced, and retesting indicates acceptable entry conditions.
    • If a hazardous atmosphere is detected during entry:
      • Each employee must leave the space immediately;
      • The space must be evaluated to determine how the hazardous atmosphere developed; and,
      • Measures must be implemented to protect employees from the hazardous atmosphere before any subsequent entry takes place.

Note: Ventilation systems and electrical tools and equipment used in existing or potentially flammable atmospheres must be explosion-proof and appropriately rated for the hazard.

Contact Information

Robin McCall-Miller, Occupational Safety Program Manager

Phone: 540-231-2341