Sunday, August 25, 2013
TYPES OF FIRST AID FIRE FIGHTING APPLIANCES
1)WATER
TYPE
a)The extinguisher consists of
a cylindrical shaped outer
container which is made of mild steel and treated
for anti-corrosion, which contain 9 ltrs. of
water. The container is pressure tested at a pressure of 350 lbs. Psi
(24 bars Approx.). It has an expansion space.
b) Gas cartridge (cO2) is stored inside
cylinder and coupled to the operating head. It contain 60 gram of CO2
charged with in the container at pressure of 35 bars which when punctured
releases the gas and pressurize the water.
c) An operating head is secured
to the outer container with a plunger and striking knob. The knob is protected
by a safety clip or cap to prevent it from accidental operation. There are
three vent holes provided on the cap to allow the pressure to release by which
explosion hazards of the extinguisher can be avoided.
OPERATION
The
water type extinguishers are operated (used) for “A” class fire. Carry the
extinguisher to the scene of fire, remove the safety clip, make sure the cap is
fully screw down and strike the knob hard, direct the water jet in heart of the
fire with the wind.
RECHARGING
a)Make sure that the vent
holes are absolutely clear on the
extinguisher head.
b)Unscrew the CO2
cartridge.
c)Wash out the outer container
and refill it with fresh water, add antifreezing chemicals if required.
d)Take new CO2
cartridge, and after making sure that the plunger is fully withdrawn screw in
the CO2 cartridge on the head. The plunger must be fully
serviceable.
e)Screw down the head fully.
f)Write down the recharging
date on the body and if rubber hose (discharge hose) is fitted make it fully
tight.
WATER TYPE STORED PRESSURE
This
extinguisher contains a cap fitted with valve group (normally of brass metal)
and a cylinder containing water and space for dry air. The extinguisher is
filled with water and air is charged into it at a pressure of 10 bars. This can
be charged from a compressed air cylinder or from a compressor. The air can be
charged through an adaptor which is fitted permanently to the extinguisher.
Test: - a) Monthly
weigh the cartridge.
b)
Pressure test.
2) FOAM
EXTINGUISHER (MECHANICAL)
FOAM
foam is a frothy substance entirely consisting of
bubbles and these bubbles contain either CO or Air.Mechanical way of
producing foam is by self aspiration of a foam solution through a foam making
branch pipe by mechanical means and it will produce 72 to 90 ltrs. of foam.
OPERATION
These extinguishers are used on “A” & “B”
classes of fire. When required take extinguisher to the scene of fire, tight
the wheel head assembly, remove the safety clip, hold the discharge hose in the
hand and strike the knob hard use the foam directly on fire.
RECHARGING
a)Unscrew the wheel head and
remove the CO2 cartridge.
b)Make sure the vent holes are
clean.
c)Wash the outer container and
fill up 8.6 ltrs of water and mixed. 4 ltr of
AFFF (Aqueous Film Forming
Forces) and dilute it properly.
d)Refill the solution is outer
container.
e)Take fresh CO2
cartridge of 90 gram to 120 gram and connect it to wheel
head.
f)Replace the wheel head
assembly and put safety clip on.
3) DRY CHEMICAL POWDER EXTINGUISHER
INTRODUCTION
various types of dry chemical powders were used for
many years. But they had various drawbacks. Powder Commonly used for class
B&C type fires are usually based on sodium bicarbonate. Potassium
bicarbonate powder is also used in many countries. Powder for dealing with
carbonaceous (class A) fires as well as class B fires known as General purpose
one based on ammonium phosphates. All dry powders are treated to improve their
flow and reduce caking.
PROPERTIES AND USES
Modern dry powder extinguisher is very
efficient. They can use for running fires in highly flammable liquids. Recent
developments however have produced powders, which are capable of dealing with
carbonaceous fires.
The
powder extinguishes the fires by stopping chain reactions occurring in the
flames. Sodium and Potassium Carbonate are found to be the best. When applied
on the flame it smokeless, the fire, draws heat and cools the flame, when it
decomposes produce CO2 and water even though it is very little. The
importance of the decomposition is that a new cathartically active, surface is
formed and that will become as a fire retardant and destroys the radicals that
propagate the chain reaction. Ammonium phosphate powder not only extinguishes the
class B fire but also class ‘A’ fires. The phosphate content of the
general-purpose powder deals with the smoldering by acting in a manner, which
is similar to that of a fore retardant.
The
normally used fire-extinguishing agents are inadequate or dangerous when used
on metal fire such as magnesium, aluminum, uranium, titanium, and zirconium
metals. A combination of sodium, potassium and barium chloride (ternary
eutectic chloride) is used for class “D” fire. The melting point is very low
and the capacity for absorbing the latent heat from the metal is very high. The
powder melt and forms a fused skin cover the metal, preventing contact with the
Oxygen in the atmosphere at the same line absorbing the heat from the metal, so
cooling it below its ignition temperature. There are two types of dry chemical
powder extinguishers (a) Stored Pressure and (b) CO2 gas pressure
type.
(a) STORED PRESSURE TYPE
The construction of the
stored pressure type Dry chemical powder extinguisher the outer container is
made of mild steel and treated for anti-corrosion cap or head is made of brass
fitted with valve group (pressure gauge, charging adaptor etc.) 10 Kg Dry
chemical powder and a space for dry air at the pressure of 10 bar/cm2.
This can be charged from a compressed air cylinder or from the compressor the
air can be charged through an adaptor, which is permanently fitted to the
extinguisher.
(b) PRECAUTIONS WHEN RECHARGING
Make sure the container is thoroughly dried, before
recharging.
Particular care should be taken to ensure that powder remaining in
discharge hose and nozzle is fully cleared. When refilling the new
powder
container is opened, the powder should be transferred
immediately into the
extinguisher and appliance sealed. Personnel
handling must take care mixing or
cross contamination should be
avoided. Some powder may react which will not be
felt at the same
time but at later stage. Only one type of powder extinguisher
be
opened at a time to avoid mixing. The examination should be
conducted only
in a clean room using dry receptor.
CO2 EXTINGUISHER
Carbon dioxide has been used for many years to extinguish
flammable liquid fires and live electronic equipment fires. Consequently it is
widely employed as an extinguishing agent in fixed installation and also in
portable extinguishers with capacities ranging from 0.9 kg to 6.8 kg of
liquefied gas.
GENERAL CHARECTERSTICS
CO2 has a number of properties making it useful for
extinguishing fire.
1.It is non-combustible and
does not react with most substances.
2.It can penetrate and spread
it all part of fire area.
3.It provides its own pressure
for discharge from extinguisher.
4.It is non-conductor of
electricity.
5.It will not damage
sophisticated electronic equipment. Under normal
condition CO2 is
colourless, odourless. It is easily liquefied by pressure
and cooling CO2 is
relatively nontoxic.
When CO2 in
liquid form release from storage cylinder there is an extremely rapid expansion
from liquid to gas which produces a refrigerating effect, that converts the
part of CO2 into “snow” (solid- particles). This snow, which has a
temperature of 79o C, soon sublimes (i.e. transformed directly from solid to
gas). It is the sublimation that produces some cooling effect. When used as an
extinguisher under suitable conditions of control and application some cooling
of the fire may be effected, but it is the extinction of the oxygen to a point
where it will no longer support combustion, which is of primary importance. In
general 1 kg of liquid CO2 in its liquid state
will produce about 5
m3 of free gas at atmospheric pressure.
OPERATION
Earlier models were operated by striking a plunger
at the head of the cylinder. This pierced a sealing disc or by actuating lever
device, but in most current models removing a safety pin and then operating the
discharge device release the gas. The essential feature about this device, what
even its type is that it should open quickly and provide a clear passage for
the liquid. If this free passage does not exist, freezing up of the valve
occurs. For this reason the small orifices in commercial valves are not
suitable. The discharge mechanism is usually designed so that, at an ambient
temperature of 15o C to 18o C not less than 95% of the
content is released in form of continuous discharge is the minimum time.
Owing
to the expansion of the discharging gas and its liability to freeze, careful
design of the discharge mechanism is essential.
A
discharge tube is fitted to the cylinder so that liquid CO2 is
released through the valve in cylinder head. Expansion may commence in the
flexible discharge tube, is fitted, but the greater part of expansion take
place in discharge horn. The ratio of expansion is 1:450. The design of the
discharge horn is very important feature of CO2 extinguisher’s its
main purpose is to stop the containment of air with the CO2 by
reducing the velocity of the gas. Without this horn the jet of CO2
gas and air acts like a blowtorch and would increase the intensity of fire.
CLASSIFICATION OF FIRE
Fire is chain reaction following elements when they
meet together eg. Burning material (or fuel),Oxygen(or air) and heat.
TYPES OF FIRE
“A” TYPE OR GENERAL FIRE
This fire
involving solid material normally of organic nature compounds of carbon in
which combustion occurs with the formation of glowing ember.
Class “A” fires are the most common and the most effective
extinguishing agent in generally water in the form of jet and spray.
TYPE “B” OR LIQUID FIRE
These are fire involving liquid; or liquefiable
solid; for the purpose of choosing effective extinguishing agent liquid may be
divided in two groups
1.One which is mixable with
water alcohol and acid
2.Those that are not mixable
with water petroleum products and edible oils etc.
Depending upon a and b the extinguishing agents are
water spray, foam, light water, vaporizing liquid CO2 and dry
chemical powder.
TYPE “C”
These are fires involving gases or liquid gasses in the
form of a liquid spillage or liquid or gas leak and these includes methane, propane,
pentane etc. Foam or dry chemical powder can be used to control the fires
involving shallow laved liquid spill water in form of spray is used to cool the
container.
TYPE “D” FIRE
These fire involving metal extinguishing agents
containing water are ineffective and even dangerous co2 and
carbonate gasses of dry powders m ay also be hazardous. If applied most metal
fires, powdered graphite powder talk, soda ash, limestone and dry sand are
normally used for class “D” Fires.
“E” ELECTRICAL FIRE
It is most considered according to present day ideas
that electrical fire constitute a class, since any five involving or started by
electrical equipment most in fact be a fire of class ‘A B & D’.
