Also in: Disaster Response and Recovery
Confined Space Air Change Time
Minutes to reach target air changes from blower CFM.
Example
You enter
- Space volume (ft^3) 2000
- Blower CFM 1000
- Target air changes 7
You get
- Minutes to purge 14 min
Checked against published worked examples from: 29 CFR 1910.146 + ACGIH ventilation engineering practice.
Details, formula, and sources
Formula or tableTime t = V × N / CFM where V is volume, N is target air changes (typically 4-7 for atmospheric clearance), CFM is the blower flow.
Source and editionOSHA 29 CFR 1910.146 (Permit-Required Confined Spaces) by section. ANSI/ASSP Z117.1 (Safety Requirements for Entering Confined Spaces) by name.
Free access29 CFR 1910.146 free at ecfr.gov; ANSI/ASSP standards licensed.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namesvolume_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