Calculator Inputs
Formula Used
This calculator estimates required stored volume using a transparent, auditable approach.
- Use refill credit only when refill is dependable under fire conditions.
- Usable fraction accounts for dead volume and suction constraints.
- Redundancy scales storage for resilience and service interruptions.
How to Use This Calculator
- Choose your unit system, then enter sprinkler design flow.
- Add hydrant and hose stream flows if they share the tank.
- Enter the required fire event duration in minutes.
- Set margin, redundancy, reserve, and usable fraction values.
- Click Calculate Storage to view results above the form.
- Use Download CSV or Download PDF for documentation.
Example Data Table
These examples are illustrative only. Always follow applicable codes and project requirements.
| Facility scenario | Sprinkler flow | Hydrants | Hose streams | Duration | Usable fraction | Margin |
|---|---|---|---|---|---|---|
| Warehouse (ordinary hazard) | 1,900 L/min | 1,000 L/min | 500 L/min | 120 min | 0.90 | 10% |
| Manufacturing (extra hazard) | 3,200 L/min | 1,500 L/min | 750 L/min | 180 min | 0.88 | 15% |
| Office (light hazard) | 950 L/min | 0 | 250 L/min | 60 min | 0.92 | 8% |
Demand drivers and design inputs
Fire water storage begins with credible flow selection. Sprinkler demand is typically the primary component, while hydrant and hose streams may be concurrent. This calculator allows additive selection so you can model a combined peak flow. Example: 1,900 L/min sprinklers + 1,000 L/min hydrants + 500 L/min hose streams equals 3,400 L/min. If hydrants are on municipal mains, you can exclude that portion and isolate tank demand.
Duration selection and duty planning
Duration converts a flow rate into a volume requirement. Common planning windows range from 60 to 240 minutes depending on hazard and protection strategy. Longer durations increase storage linearly, so select the controlling scenario, not an average event. A 3,400 L/min demand sustained for 120 minutes produces 408,000 liters before margins. At 180 minutes, the same demand becomes 612,000 liters, a 50% increase.
Resilience factors and usable volume
Real tanks rarely deliver 100% of their geometric volume. Suction limits, sediment allowance, and minimum operating level reduce usable water, often to 0.85–0.95. The usable fraction adjusts gross storage upward to protect pump net positive suction head and maintain stable flow. Redundancy factors from 1.00 to 1.50 add contingency for maintenance, single point failures, or supply interruptions. A 1.20 factor means 20% extra volume beyond net demand.
Refill assumptions and supply reliability
If a dependable refill source exists, the calculator can credit refill volume during the event. Refill credit equals refill rate multiplied by duration, reducing net demand but never below zero. Use this feature conservatively: power loss, valve isolation, and freezing conditions can reduce refill capacity. For high consequence facilities, treat refill as secondary and size storage to stand alone. When enabled, document refill rate and isolation valves keeping it available.
Documentation and audit readiness
Fire protection reviews benefit from consistent, traceable inputs. Record unit system, component flows, duration, margins, redundancy, fixed reserve, and usable fraction. Exported CSV supports peer checks, while the PDF snapshot aids submittals and insurer discussions. Keeping notes inside the form captures assumptions, hazard class, and the rationale behind every multiplier for future modifications. Pair the result with pump curve data and pressure requirements to complete the final design record.
FAQs
1) Should I include hydrants and hose streams?
Include them only if they draw from the same stored supply during the design fire. If hydrants are on a separate main or dedicated reservoir, exclude that demand to avoid oversizing.
2) What does “usable tank fraction” represent?
It represents the portion of geometric volume that can be reliably delivered to pumps. It accounts for low-level cutoff, suction lift limits, sediment space, and operational constraints.
3) When is refill credit appropriate?
Use refill credit only when the refill source is dependable during fire conditions, including power loss and isolation scenarios. If reliability is uncertain, size storage without refill credit and treat refill as bonus.
4) How do safety margin and redundancy differ?
Safety margin covers uncertainty in inputs and operating variability. Redundancy covers resilience needs such as maintenance windows, partial outages, and single point failures. Using both creates conservative, review-friendly storage sizing.
5) Which units should I use for reserve volume?
Reserve volume follows your selected unit system. If you choose metric, reserve is in liters. If you choose US customary, reserve is in US gallons, then converted internally for consistent calculations.
6) Is this calculator a substitute for code compliance?
No. It supports planning and documentation by making assumptions explicit. Final storage must be verified against local codes, insurer criteria, hydraulic calculations, pump curves, and the project’s authority having jurisdiction.