NFPA 1142 Rural Water Supply
Minimum on-site water supply WS = (V x construction classification number) / occupancy hazard classification number...
Example
You enter
- Building volume (ft³; footprint x avg ceiling) 30000
- Occupancy Hazard Classification (NFPA 1142 Ch. 5, OHC 3-7) 7
- Construction class (NFPA 1142 Ch. 6) V
- Exposure within 50 ft false
- UL-listed sprinkler system present false
You get
- Required minimum fire-flow (gal) 6429
Checked against published worked examples from: NFPA.
Details, formula, and sources
ScopeMinimum on-site water supply WS = (V x construction classification number) / occupancy hazard classification number per NFPA 1142 Ch. 4, with 1.5x exposure and 0.5x sprinkler multipliers; recommended tanker trip count.
Formula or tableWS = (V * CCN) / OHC per NFPA 1142 Ch. 4 (Occupancy Hazard Classification Number OHC 3-7 divides; Construction Classification Number CCN 0.5-1.5). 1.5x exposure multiplier when adjacent structure within 50 ft. 0.5x sprinkler reduction when UL-listed system present.
Source and editionNFPA 1142-2022 (Standard on Water Supplies for Suburban and Rural Firefighting) Ch. 4.
Free accessnfpa.org/freeaccess.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namesvolume_ft3, occupancy_class, construction_class, exposure_within_50_ft, sprinkler_listed, Q_min_gal
- Occupancy factors NFPA 1142 Ch. 5 Occupancy Hazard Classification Number (OHC 3 severe to 7 light; a divisor)NFPA 1142-2022 Ch. 5
- Construction factors Class I-V per NFPA 1142 Ch. 6NFPA 1142-2022 Ch. 6
- Exposure multiplier 1.5x when adjacent structure within 50 ftNFPA 1142-2022 Ch. 4
- Sprinkler reduction 0.5x contingent on confirmed UL-listed systemNFPA 1142-2022 Ch. 4; AHJ inspection governs
- Standard tanker sizes 1000 / 1500 / 2000 / 3000 galcommon apparatus sizing