Quantity of Water by National Board of Fire Underwriters Calculator

Water Quantity Formula:

\[ Q = 4637 \times \sqrt{P} \times (1 - (0.01 \times \sqrt{P})) \]

Quantity of Water (Liters Per Minute):

1. What is the Quantity of Water Calculator?

Definition: This calculator estimates the quantity of water required for firefighting based on population size, according to the National Board of Fire Underwriters formula.

Purpose: It helps urban planners and fire departments determine water supply requirements for fire protection in a community.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ Q = 4637 \times \sqrt{P} \times (1 - (0.01 \times \sqrt{P})) \]

Where:

\( Q \) — Quantity of water (liters per minute)
\( P \) — Population (in thousands)

Explanation: The formula accounts for the non-linear relationship between population size and water demand for firefighting.

3. Importance of Water Quantity Calculation

Details: Proper water quantity estimation ensures adequate fire protection, helps design water supply systems, and meets insurance requirements.

4. Using the Calculator

Tips: Enter the population in thousands (e.g., 20 for 20,000). The result includes a ±5% margin to account for variations.

5. Frequently Asked Questions (FAQ)

Q1: Why does the formula use square root of population?
A: Fire risk doesn't increase linearly with population. The square root accounts for the fact that fire occurrence grows more slowly than population.

Q2: What does the ±5% represent?
A: It accounts for variations in building density, construction types, and other local factors affecting water demand.

Q3: Is this formula still used today?
A: While modern methods exist, this remains a benchmark for basic fire protection water requirements in many jurisdictions.

Q4: How does this relate to fire hydrant spacing?
A: The calculated water quantity helps determine how many hydrants are needed and their spacing to deliver required flow.

Q5: What about high-rise buildings?
A: This formula provides baseline requirements. High-rises typically need additional water supply and pressure considerations.