Accurate fire water demand calculation is vital for a reliable fire-protection system. Understanding flow rate, duration, components, and standards ensures safety, compliance, and effective system design.
Fire water demand refers to the quantity (flow and volume) of water that must be available to supply firefighting or cooling operations in the worst-case fire scenario within a facility or installation. The purpose is to ensure the fire-protection system can deliver sufficient water to extinguish or control fire, protect exposure equipment, meet regulatory obligations and ensure safety of people and assets.
Identify credible worst-case fire scenarios: largest tank on fire, two major fires simultaneously, jet fire, storage fire, process unit fire. Determine affected equipment and exposure considerations, and define the design basis (number of fires, duration).
Calculate:
Multiply flow rate by duration to determine required fire-water storage (plus make-up water or reliability allowances). Example: OISD STD-117 uses design flow × 4 hours where make-up water is unavailable.
Ensure pumps deliver required flow and pressure (e.g., 7 kg/cm² at farthest hydrant as per OISD). Hydraulic network design must account for friction losses and provide redundancy.
Cooling: π × D × H × 3 L/min/m² for tank on fire. Nearby tanks (within R + 30 m) use 3 L/min/m²; others 1 L/min/m².
Foam: apply as per rim-seal and surface area calculations.
Includes flow for fixed spray, hydrants, monitors, and foam systems. Often requires a risk-based approach and simultaneous fire planning.
Design must consider two major fires simultaneously for large installations (OISD STD-116). Include contingency for backup pumps and make-up water.
Storage volume = flow × duration (+ margin). Example: 4 hours as per OISD STD-117.
Ensure separation from process area, alarms, and make-up provisions.
Pumps must provide flow and 7 kg/cm² pressure at farthest hydrant.
Include redundancy (diesel + electric drives, standby units, auto-changeover).
Looped mains, friction loss analysis, valve spacing, hydrant/monitor layout and hydraulic modeling are essential.
Regular pump run tests, hydrant flow checks, foam testing, and documentation per OISD.
Example: Floating-roof tank 79 m dia × 14.4 m height.
Risk-based approach (NFPA/API) calculates maximum flow from jet/pool fire, spray systems, hydrants, and monitors to size pumps and storage.
Always apply correct design duration (4 hours + foam) and simultaneous fire requirement per OISD STD-116/117.
Do not focus only on sprinklers—include monitors, hoses, and foam systems.
Ensure redundancy, margin, and testing programs are in place.
Perform audits, hydraulic simulations, and recalculate after plant expansion or layout change. Maintain full documentation for review and compliance.
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Fire safety audit to assess compliance, risks, and system effectiveness.
Evaluation of fire protection adequacy based on risk and regulations.
Automatic fire sprinkler system for reliable fire detection and suppression.
Calculation of combustible fire load to determine fire risk levels.
Design, engineer, and audit fire protection systems ensuring reliable performance, asset safety, and adherence to national safety standards.
Hydraulic calculations ensuring adequate pressure and fire system performance.
Accurate fire line sizing for optimal water flow efficiency.
Spray sprinkler system design for rapid industrial fire suppression.
Fire and gas detector mapping for early hazard detection.
Fire risk assessment identifying hazards and preventive control measures.
Fireline sizing to ensure sufficient flow during fire emergencies.
Fire protection system maintenance for compliance, reliability, and safety.
Typically 4 hours based on design flow when no make-up water is available (OISD STD-117).
Include foam or spray for hydrocarbon fires, per OISD/NFPA guidance.
Kuichling’s, Freeman’s, and Buston’s formulas are used for population-based estimation
No. OISD STD-116 requires two major fires simultaneously for large installations.
After any facility expansion, hazard reclassification, or major modification.
Ignoring simultaneous fires, under-estimating foam/hose demand, or missing redundancy and testing.
