Smoke Ejector / Ventilation CFM (NFPA 1500)
Required CFM for a target air-change rate, fans needed, time to one air change.
Example
You enter
- Room length (ft) 30
- Room width (ft) 40
- Ceiling height (ft) 10
- Target air changes per hour 5
- Ejector fan CFM rating 4000
- Exhaust opening (ft^2) 12
- Entry opening (ft^2) 10
You get
- Required CFM for target ACH 1000
- Fans needed 1
- Time to one air change 3 min
- Exhaust-to-entry ratio 1.2
Details, formula, and sources
Required CFM for a target air-change rate, fans needed, time to one air change, and the exhaust-to-entry opening ratio for negative-pressure ventilation. SOP and incident command govern.
Required CFM = volume × ACH / 60. Fans = ceil(required CFM / per-fan rating). Time to one air change = volume / actual CFM. Exhaust-to-entry opening ratio drives PPV efficiency (1:1 to 1.5:1).
NFPA 1500 §8.5 (apparatus and equipment) by name; IFSTA Essentials of Fire Fighting ventilation chapter by name.
NFPA 1500 read-only at nfpa.org/freeaccess; NFA materials free at usfa.fema.gov.
Estimate. AHJ and licensed fire protection engineer govern.
Field names used by the API: length_ft, width_ft, height_ft, target_ach, fan_cfm, exhaust_opening_ft2, entry_opening_ft2, cfm_required, fans, time_to_one_change_min, opening_ratio
- Default target ACH 5 air changes per hour for post-fire negative-pressure ventilationIFSTA Essentials typical
- Opening ratio exhaust slightly larger than entry (1:1 to 1.5:1) for efficient PPVIFSTA Essentials / PPV best practice