WATER FOR FIRE
PROTECTION (Chapter 26)

Basic factors of fire
– Rapid oxidation of combustible materials
– A combination of oxygen, fuel, and heat is
required to start a fire.

Classification of fire hazards
 Classification of occupancy hazards
WATER FOR FIRE PROTECTION
(Additional information)

Objectives in fire safety
– Protection of life


Evacuation of people the time interval between detection of
fire and arrival of fire fighters.
Providing adequate number of fire exits and clearly defined
access (i.e. corridors, hallways, etc.) to exits.
– Absolute minimum width of an exit access is 28".
– In order to accommodate adults using various walking aids,
corridors should be at least 36" wide.

The standard unit of exit width computation is 22" (i.e. 22" = 1
exit unit).
– Exit Width Units = Floor area of the building in sq. ft./(occupant
density in sq. ft./person)* (Capacity per unit of exit width)
WATER FOR FIRE PROTECTION
(Additional information)

Minimum exit requirements:
–
–
–
–
–

Basement: 2
Every building floor: 2
Building with 50 occupants or more: 2
Building with 500 occupants or more: 3
Building with 1,000 occupants or more: 4
Maximum distance of a fire exit from any part of the building
– 100 to 200 ft. for unspriklered spaces
– 150 to 300 ft. for sprinklered spaces.
– Protection of property
– Continuity of operation
WATER FOR FIRE PROTECTION

Methods for fire detection

Methods of fire control
– Standpipe systems
– Automatic sprinkler systems

Piping design
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–
–

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Hydraulic method: Hazen-Williamson formula
Use of piping schedule
Flow rate of sprinklers
Sprinklers on a branch line
Protection area per sprinkler
Maximum spacing between sprinklers
DESIGN OF SPRINKLER SYSTEMS
(Additional information)

Residual pressure of the sprinkler system
–
–

pressure remaining in a system while water is being discharged from the outlets
sprinkler systems are usually designed for a maximum working pressure of 175 psi.
Density of Water Flow (D)
–
required water flow from a sprinkler in gallons per square foot of area of operation



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Light hazard: 0.07 to 0.1 gpm/sq.ft.
Ordinary hazard: 0.1 to 0.2 gpm/sq.ft.
Extra hazard: 0.2 to 0.4 gpm/sq.ft.
Size of sprinklers
–
Find required flow rate (in gpm) of a sprinkler (Density of water flow * Maximum
coverage)
– Find out k-factor to determine the size of the sprinklers
 Q = K* p, where Q = flow rate in GPM, K = flow constant of sprinklers, p = residual
pressure in psi

Determine the size of the piping system
–
Use the method for sizing water supply pipes (either pipe sizing formula or piping
schedule)
Sprinkler head sizes (Additional
information)
K-factor
Nominal orifice size in inch
1.3-1.5
¼
1.8-2.0
5/16
2.6-2.9
3/8
4.0-4.4
7/16
5.3-5.8
½
7.4-8.2
17/32
11.0-11.5
5/8
13.5-14.5
¾
WATER FOR FIRE PROTECTION
(Additional information)

Water demand for fire suppression
– Area of Sprinkler Operation (ASOP)
 Only a small part of the sprinkler systems need to be
operated during the early stage of fire. Codes,
therefore, require only a small area of the building to
be calculated for simultaneous flow demand. This
area, called the area of sprinkler operation (ASOP),
for different hazard classifications is as follows:
– Light: 1500 - 3000 sq. ft.
– Ordinary: 1500 - 4000 sq. ft.
– Extra: 2500 - 5000 sq. ft.
WATER FOR FIRE PROTECTION
(Additional information)
– Density of Water Flow (D)

required water flow from a sprinkler in gallons per square foot
of area of operation
– Light hazard: 0.07 to 0.1 gpm/sq.ft.
– Ordinary hazard: 0.1 to 0.2 gpm/sq.ft.
– Extra hazard: 0.2 to 0.4 gpm/sq.ft.
– Hose Stream Demand (HSD)

water demand of hoses, both inside and outside
– Light hazard: 100 gpm
– Ordinary hazard: 250 gpm
– Extra hazard: 500 gpm
– Overage Factor (OVF)
 Usually 1.1
– Total Water Demand in gpm = ASOP * D * OVF + HSD
Other methods of fire
suppression

Carbon dioxide
 Dry chemicals
 Foam systems
 Halogenated agents