Fire Flow

What Is Fire Flow?

Fire flow is the calculated volume of water — expressed in gallons per minute (GPM) — required to suppress a fire in a given structure, based on its square footage, construction type, occupancy, and exposure risk. The National Fire Academy (NFA) formula estimates needed fire flow as the building's involved area in square feet divided by 3 (length × width ÷ 3 = GPM), while ISO grading methods factor in construction class, effective area, occupancy hazard, and exposure distances to calculate required flow for insurance rating purposes.

Why Fire Flow Matters on the Fireground

Underestimating fire flow means you run out of water before the fire is knocked down, while overestimating wastes capacity that could supply additional lines or protect exposures. An accurate fire flow calculation tells the pump operator how many lines the water supply can sustain and whether relay pumping, additional hydrants, or tanker shuttles are needed.

Relevant NFPA Standards

• NFPA 1010: Standard on Professional Qualifications for Firefighters
• NFPA 1550: Standard for Emergency Responder Health and Safety

Field Procedures & Tactical Steps

1. Estimate involved area (length × width of the fire-involved portion of the building) and apply the NFA formula: area ÷ 3 = required GPM.
2. Add 25% for each significant exposure building within 30 feet of the fire structure.
3. Determine available water supply — hydrant flow test data (static pressure minus residual pressure × GPM at 20 PSI residual), tanker shuttle capacity, or draft source.
4. Compare available supply to required fire flow and decide whether the attack plan is sustainable or needs additional supply.
5. Assign the pump operator to monitor tank level and intake pressure continuously, calling for additional water sources before depletion.

Common Context & Application

Calculated during pre-incident planning for target hazards and estimated in real time by the incident commander and pump operator during the initial size-up to determine whether the available water supply can support the attack plan.

Frequently Asked Questions about Fire Flow