Fire demand is the amount of water required to extinguish fire.
The water required for fire fighting in a given area.
Although the actual amount of water used in a year is small for fire fighting. But the rate of use is large. Generally the water pressure is 20 Psi.
Method for estimation of fire demand
There are two methods for the estimation of fire demand.
- National board of fire under writers formula.
- Insurance service office formula.
Determination of fire demand considers construction, occupancy, exposure and communication of each building.
The process of fire fighting water requires consideration of a number of points. These are:
- Quality of water
- Water demand i.e. flow rate, storage and available pressure
- Process for access via fire hydrants
Although water is inexpensive and readily available, itís processing and distribution carries a significant cost in terms of infrastructure cost. The main component of this cost is in the capital works required to filter and sterilise the raw water supply and
produce a potable water supply.
The cost of providing a water reticulation supply to meet the needs of fire fighting over and above a potable supply
was evaluated in a study undertaken by the National Research Council Canada (NRCC 1997). This study concluded that it was more cost effective to provide a tanker supply for fire fighting rather than increasing the size of the water processing and reticulation system.
The use of alternative supplies such as ponds, streams and swimming pools is common in rural areas where reticulated supplies do not exist.
The quality of water required for fire-fighting purposes is much lower that that required for human consumption and hence it is appropriate to consider other alternative water supplies to supplement large reticulated supplies. With the development of rainwater storage and ìgrey waterî storage the ability exists to make this supply available for fire fighting purposes. Another potential source of fire fighting water is from the runoff collection tanks.
The normal method of gaining access to a reticulated supply is via in ground hydrants. These are spaced at regular intervals along public roads in accordance with either a spacing or area requirement.