Page 74 - Science Class 08
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dioxide, sand or even soil will help in case sound. A large amount of gas formed in the
of oil fire. reac on is liberated. Such a reac on is called
v Electrical fire should not be tried to explosion. It can also take place if pressure is
ex nguish by using water or foam, as water applied on the cracker.
and foam conduct electricity at high voltage. FLAME
So, when water or foam is thrown on the You see various substances burning. You must
burning electricity wires, it may electrocute have no ced that some substances burn with
the person involved. So, using carbon flame whereas some do not give any flame. Do
tetrachloride as a fire ex nguisher, we can you know why? Actually, substances which
cut off fire. Since carbon tetrachloride vaporise will only produce a flame.
vapours are heavier than air, they se le
For example, LPG, wax, oil, etc:
down on the burning material and cut off
the air supply. Carbon dioxide and dry sand When a candle burns, hot molten rises up
may also be used. in the wick and vapourises. Wax vapour
combines with oxygen producing heat and
light.
When a substance burns in sufficient supply of
Fire accident can occur anywhere and
any me. Therefore, you should be alert and air, a complete combus on takes place and the
prepared to face such incidents. You should substance produces a non-luminous or flame.
remember the telephone number of fire But in insufficient supply of oxygen, a flame of
service, ambulance service, hospital, etc. of yellow colour is obtained. This is because of the
your area. Write the numbers here. glowing of unburnt carbon atoms.
Fire service : When wood or charcoal is ignited, the vola le
Ambulance : substances present vapourise and burn with a
Hospital : flame in the beginning.
When a candle is lit, the heat from the flame
melts the wax. The molten wax vapourises and
combines with oxygen and burn.
1. Why some substances are combus ble
while some are not?
2. What is the importance of the property
of combus on?
3. What is igni on temperature?
4. What is rapid combus on?
5. Give one example of slow combus on.
6. Why do we use foam fire ex nguisher?
Cracker
When a cracker is ignited, a sudden reac on
takes place with the evolu on of heat, light and Flame
74 Science-8
