Confined Space Air Change Time

Minutes to reach target air changes from blower CFM.

Example

You enter

You get

Details, formula, and sources

Time t = V × N / CFM where V is volume, N is target air changes (typically 4-7 for atmospheric clearance), CFM is the blower flow.

OSHA 29 CFR 1910.146 (Permit-Required Confined Spaces) by section. ANSI/ASSP Z117.1 (Safety Requirements for Entering Confined Spaces) by name.

29 CFR 1910.146 free at ecfr.gov; ANSI/ASSP standards licensed.

Estimate. AHJ and licensed fire protection engineer govern.

Field names used by the API: volume_ft3, blower_cfm, target_purges, minutes

Default target air changes 7 ACH for full atmospheric clearance unless user suppliesOSHA 29 CFR 1910.146 / ANSI Z117.1

Details, formula, and sources

Time t = V × N / CFM where V is volume, N is target air changes (typically 4-7 for atmospheric clearance), CFM is the blower flow.

OSHA 29 CFR 1910.146 (Permit-Required Confined Spaces) by section. ANSI/ASSP Z117.1 (Safety Requirements for Entering Confined Spaces) by name.

29 CFR 1910.146 free at ecfr.gov; ANSI/ASSP standards licensed.

Estimate. AHJ and licensed fire protection engineer govern.

Default target air changes 7 ACH for full atmospheric clearance unless user suppliesOSHA 29 CFR 1910.146 / ANSI Z117.1