Automatic Sprinklers:-
"CLICK---Sprinkler head actuating. "
Introduction:
Since one of the most important principles of successful fire extinction is to attack an outbreak immediately,it follows that any device which can detect a fire automatically and then help to extinguish it with a minimum fire loss will prove to be of great value.Automatic sprinkler systems using water as the extinguishing medium have been universally adopted for this purpose.So,the function of the automatic sprinkler may be summarized as:
（i) To detect the fire.
（ii)To attack the fire.
（iii)To prevent the spread of fire..
（iv)To activate the alarm.
The system consists of a range of piping fitted at the ceiling level on each floor of
the building to be protected,the pipe work terminating at the control valve which is connected to one or more water supplies.
At intervals along the piping,there are fitted sealed outlets called"Sprinkler
heads"which at the predetermined temperature will open and allow water to be projected on to the area below.If more than one head opens,the area covered by
each overlaps that covered by the next head,so that all the floor space is covered. The operation of a sprinkler head leads to the opening of a valve and also causes an alarm bell to ring.
"CLICK--Working principle (animation) "
Types of Sprinklers:
Tere are six types of standard sprinkler svstem are in use which are as rollows.
（a)Wet pipe.
（b)Dry pipe.
（c)Alternate wet and dry pipe.
（d)Tail-end dry pipe[used in conjunction with(A)and(B)]
（e)Tail-end alternate[used in conjunction with(A)]
（f)Pre-action.
（g)Deluge System.
（A)Wet Pipe Systems:
This is simplest and most commonly used,where the range pipes are not exposed to temperature below freezing.Pipes are kept permanently filled with water and heads point downward.Maximum number of heads,1250 for one set of controlling valves.
The principal controls of such system are:
（i) A stop valve on each separate source of supply.
（ii) A non-return valve on each source of supply.
（iii) An installation main stop valve to cut-off the flow of water to the system
after a head is opened and the fire has been extinguished.
（iv) An alarm valve which lifts when water enters the sprinkler feed pipes and
permits the passage of water to the alarm gong.
（v) A test and drain valve,used for providing the water supply to the installation and to empty the system when necessary.The size of the valve is 40 mm in extra light,hazard and 50 mm in extra high hazard installations.
（B)Dry Pipe System:
This system is used in exposed places such as cold storage,etc.or any place which may be exposed to freezing conditions.Generally range piping are filled with compressed air.Differential valve holds back water pressure. Accelerator normally fitted in the system.Maximum number of heads,700(800 with accelerator)for one.
set of controlling valve.The sprinklers must be installed in the upright position above the range pipes.
Efficiency of Dry pipe System
According to the fire records,more sprinklers open on the average at fires with dry pipe than with wet pipe system.This tends to show that the control of fire is not as prompt with dry pipe systems.However,in most classes of occupancy,and specially those of light and moderate hazard,dry pipe systems have shown generally good results and when properly maintained,can be relied upon to.satisfactorily extinguish or control fires.
（C)Alternate Wet and Dry System:
This system is generally installed in the buildings without adequate artificial heating where would be liable to freeze during winter.The system operates on the wet principle in the summer and dry in winter.When,on the wet system,the differential air valve is placed out of commission and the alarm valve only used.A wet system is preferred as some delay is caused before water reaches the first sprinkler head when operating in the dry system.Accelerator generally fitted. Maximum number of heads 700(800 with accelerator)for each set of controlling valve.
（D)+(E)Tail-End System(Dry Pipe or Alternate):
These systems are essentially similar to those previously described,except that they are of comparatively small extent and form extensions to standard sprinkler installations.
They are permitted in the following circumstances:
（1)As extension to a wet pipe system in an comparatively small area-
（a)Where there is possible frost danger in an otherwise adequately heated building where the tail end would be on alternate wet and dry pipe principle,and
（b)In high temperature areas or stoves where the tail-end would be on dry pipe
principle.
（2)As extension to an alternate wet and dry pipe system in high temperature areas or stoves when the tail-end systems would be on the dry pipe principle.Sprinklers in tail-end systems must be installed in the upright position above the lines of pipes,an exception being if approved dry pendent pattern sprinklers are installed. The number of sprinklers in a group of a tail-end system controlled by one set of wet pipe system or alternate wet and dry pipe system valve,must not exceed 250 in the aggregate,with not more than 100 sprinklers on any one tail-end system.
（F)Pre-Action System:
A pre-action system is a combination of a standard sprinkler system and an
independent approved system of heat and smoke detectors installed in the same areas as the sprinklers.In general,heat or smoke detectors operate prior to the sprinklers and so a"pre-action valve"will open to allow water to flow into the sprinkler pipe work before the first sprinkler operates.The sprinkler system pipe work is normally charged with air under pressure and is monitored,so that an alarm
is given on reduction of air pressure.
Sprinklers Heads:
There are many different designs of sprinkler head, but they may be divided Broadly into two categories:
(A) Fusible solder type- Those in which operating media is fusible solder.
(B) Quartzoid bulb type- Those in which the bulb is raptured by the expansion of a contained liquid.
(C) Location and area covered by a sprinkler.
Sprinkler design ensures that the water shall be deflected on to the ceiling and out in a wide circle which will overlap the distribution from the next head. The deflector should be between 75mm and 150mm below ceilings and roofs in general. To ensure efficiency of sprinkler protection, a clear space of at least 500mm must always be maintained below the sprinkler deflectors throughout the room. For high piled combustible stock, an increased clearance of 1 meter or more must be provided.
(4) Grading of system:
According to risk categories of the occupancies, the following gradations are made:
a) Extra light hazard (XLH)
These are non-industrial occupancies where the amount and combustibility of the contents are low.
b) Ordinary hazards [OH1, OH2, OH3, OH3(S) ]
These includes commercial and industrial occupancies involving the handling, processing and storage of mainly ordinary combustible materials, unlikely to develop intensity burning fires in the initial state.
c) Extra High hazard (XHH)
This category covers commercial and industrial occupancies having abnormal fre loads as follows:-
i)Where the materials handled or processed are mainly of an extra hazardous nature likely to develop rapid and intensity burning fires.
ii) Involving the high piling of goods.
(5) Patterns of Sprinklers:
The following types of sprinklers are acceptable for general use:
a) Conventional pattern
These produce a spherical type of discharge with a proportion of the water thrown upwards to the ceiling. They may be installed upright or pendent.
b) Spray pattern:
A hemispherical discharge below the plane of the deflector is produced by this type with little or no water being discharges upwards to the ceiling.
c) Ceiling flush pattern.
This type is for use with concealed pipe work. The heads are installed pendent with plate or base flush to the ceiling and with the heat sensitive element below the ceiling line.
d) Sidewall Pattern
This type is installed along the walls of a room close to the ceiling and produces a discharge pattern resembling one quarter of a sphere with a proportion discharging on the wall behind the sprinkler. It can be used to avoid dripping from teh sprinkler and pipe work at the ceiling and for aesthetic reasons or for reasons of access where sprinklers at the ceiling are not acceptable.
e) Dry pendent pattern:
These are designed for use with dry or alternate dry and wet pipe systems, where it is not practicable to install standard sprinklers in the upright position, or on a wet pipe system where the sprinklers may be exposed to frost conditions.
f) Dry upright pattern:
These are nominally the same as deta pendent pattern sprinklers.
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