Water Demand Formula for Fire Fighting – Environmental Engineering
FIRE DEMAND FORMULA
Water required for fire fighting is usually known as fire demand . Rate of fire demand is treated as a function of population and is worked out on the basis of empirical formula as follow
1. Kuichling Formula

where ,
Q = Amount of water required in liters/minute
P = Population in thousand
2. Freeman Formula

where
Q = Amount of water required in liters/minute
P = Population in thousand
F = number of simultaneous fire streams
3. National Board of Fire Under Writers Formula
(A) For Central Congested High Valued City
(1) Where Population < 200000

(2) Where Population > 200000
For First Fire(lit/minute)
For Second Fire(lit/minute) Q=9100 to 36400 
(B) For Residential City
No.  Type of Building  Amount of Water Required (Q) 

1.  Small or Low Buildings  Q=2200 lit/minute 
2.  Larger or higher buildings  Q=4500 lit/minute 
3.  Apartment, High Value Residences,Tenements  Q=7650 to 13500 lit/minute 
4.  Three Storeyed Buildings in Density Builtup Sections  Q=27000 lit/minute 
4. Buston’s Formula

where
Q = Amount of water required in liters/minute
P = Population in thousand
5. Frequency of fire may occur
The above formulae for water demand donot take into account the frequency of fire may occur.It may be determined from the following expression :

where
t = Duration of fire in minutes
T =Period of occurance of fire in years
Note: The recommended minimum values for the above formula are t=30minutes, T = 1 year