ISO Needed Fire Flow
The fire flow ISO expects for a building, in gpm.
Example
You enter
- Footprint area (ft²) 5000
- Stories 2
- Construction class 2
- Occupancy factor Oi (0.75-1.25) 1
- Exposure distance (ft) 50
You get
- F factor 1
- A eff (ft²) 7500
- Construction factor Ci 1500
- Exposure factor X 0
- Needed Fire Flow (NFF) 1500
Checked against published worked examples from: ISO Public Protection Classification (PPC) Schedule (cited by name).
Details, formula, and sources
ScopeNFF = Ci × Oi × (1 + (X + P)) per the ISO Public Protection Classification; Ci = 18 × F × sqrt(A) by construction class, A the largest floor plus 50% of the others (25% of up to two for fire-resistive classes with protected openings). X applies only to an exposure within 40 ft. Rounded to 250 gpm (500 above 2,500); capped at 12,000 gpm.
Formula or tableNFF = Ci × Oi × (1 + (X + P)) where Ci = 18 × F × sqrt(A_eff). F per construction class (Frame 1.5 / Joisted masonry 1.0 / Noncombustible and Masonry-noncombustible 0.8 / Modified-FR and Fire-resistive 0.6). A_eff = largest floor + 50% of all other floors (Classes 1-4); Classes 5-6: + 25% of up to the two other largest floors with protected vertical openings, + 50% of up to eight if unprotected (ISO Guide for Determination of Needed Fire Flow, 2014, ch. 2 sec. 4c). Ci rounded to 250 gpm, 500 min, 8,000 max for Classes 1-2 and 6,000 for Classes 3-6 or a one-story building (sec. 5). X = exposure factor from ISO Table 330A(1-3) for an exposure within 40 ft, none beyond (ch. 3 sec. 16); P = communication factor; (X + P) limited to 0.60. NFF rounded to 250 gpm below 2,500 and to 500 above; floor 500, cap 12,000 gpm.
Source and editionISO Public Protection Classification (PPC) Schedule by name. Cited by name only; the schedule's commentary is not reproduced.
Free accessISO PPC Schedule licensed; class-factor table free in published fire-protection texts and at most state insurance department outreach.
What governsEstimate. AHJ and licensed fire protection engineer govern.
API field namesarea_ft2, stories, construction_class, occupancy_factor, exposure_distance_ft, F_factor, A_eff_ft2, Ci_capped, X_exposure, NFF_gpm
- Construction-class F table 1=1.5 / 2=1.0 / 3=4=0.8 / 5=6=0.6ISO PPC
- Cap on Ci 8,000 gpm (Classes 1-2), 6,000 gpm (Classes 3-6, or any one-story building), rounded to 250 and at least 500, before X / P / OiISO Guide for Determination of Needed Fire Flow (2014), ch. 2 sec. 5
- Round increment / floor / cap 250 gpm (500 above 2,500 gpm) / 500 gpm / 12,000 gpmISO PPC