Safety Engineering: Chapter_2 Types Of Fire and Fire Fighting Methods...

Safety Engineering: Chapter_2 Types Of Fire and Fire Fighting Methods...: 1.0 Classes Of Fire "A" Class Fire : solid fuels , e.g wood, paper,cotton. "B" Class Fire : liquid fuels. e.g petrol , diesel , kero...

1.0 introduction

                          fire is an external sign of chemical reaction, usually the combustion of carbon and or hydrogen with oxygen, resulting in release if energy in form of heat, light and sound.

2.0 fire triangle

there are basic 3 element need to produce fire.
1) HEAT
2) FUEL
3) OXYGEN
                         if one of component is not presents the fire will not created.

3.0 FIRE TETRAHEDRON.

            beside 3 elements there is forth element which is essential for continuation of fire once ignited.this is known as "CHAIN REACTION".
            once fire occurs the burned substunce produce lots of heat which tends to burn remaining fuel substance.this reaction occurs again and again.which is called "chain reaction".
            fire is OXIDATION process which produce heat its is also called EXOTHERMIC reaction..

OXIDATION  = EXOTHERMIC R.   = PRODUCE HEAT.
REDUCTION = ENDOTHERMIC R. = ABSORB HEAT.

4.0 TYPE OF FUELS.

                                    FUEL: a matter which can readily burn is called "FUEL".
TYPES OF FUEL
1) SOLID FUEL  :  WOOD, PAPER,COTTON .

             A) TINDER FUEL : occupy more then 20sqcm/gm.
             B) KINDLING F.  : occupy 2-20sqcm/gm.
             C) BULK  F.         : occupy 0.04-2sqcm/gm.

2) LIQUID FUEL :   PETROL, DIESEL, KEROSENE ETC..

             A) LIGHTER THEN WATER : which has density less then water(water density= 1000kg/m3)
                                                              e.g:  PETROL , DIESEL.

           B) HEAVIER THEN WATER: have density greater then water..                                                                                                                    e.g CARBON DI-DISULPHIDE.(CS2 = 1300KG/cube M).

           C) MISCIBLE IN WATER : which mix in water.. e.g  ALCOHOL.

3) GASEOUS FUEL : LPG, CNG, HYDROGEN..

           A) LIGHTER THEN AIR : which has vapor density less then air (air = 1.22521 kg/m³).
       
           B) HEAVIER THEN AIR :  which has vapor density greater then air.  e. g  LPG.

5.0 AIR

               air is composed of two main gases, oxygen and nitrogen. other co2, helium etc are negligible. air contains 21 % oxygen is "NONFLAMMABLE" it just support combustion process.
              minimum percentage of oxygen in air required to support combustion is 16%.

6.0 HEAT

A) DEFINITION : heat is a form of energy. it measured in calories and B.T.U(Fahrenheit = 1 b.t.u )

B) UNITS:

                  CALORY : THE AMOUNT OF HEAT REQUIRE TO RAISE 1 DEGREE TEMP OF 1 GRAM  WATER IS CALLED 1 CALORY.

                 B.T.U  :  ENERGY REQUIRE TO RAISE 1 DEGREE TEMP OF 1 POUND WATER ..
                               (1 B.T.U = 1 FAHRENHEIT )
C) SPECIFIC HEAT : ENERGY REQUIRED TO RAISE 1 DEGREE OF ANY 1 gm SUBSTANCE.

D) LATENT HEAT :  1. LATENT HEAT OF VAPORIZATION.
                                  2. LATENT HEAT OF FREEZING

LATENT HEAT OF VAPORIZATION. : amount of heat required to conver 1 gm of  water in to vapor is called lattent heat of vaporization of water.(at 100 degree , 540 calories/gm needed for water)

LATENT HEAT OF FREEZING : amount of heat required to conver 1 gm of  water in to solid ice is called lattent heat of vaporization of water.(at 0 degree , 80 calories/gm needed to convert water to ice)

7.0 transmission of heat.

1) conduction

               the heat travels through the molecule of substance without movement of molecule themselves.(molecule doesn't travels.)









2) convection :

 

          when the fluid (liquid and gas) heated the expands so the heated molecules become lighter and moves upward and cold molecules takes place . this process continues.




3) radiation :

             in this way heat travels without any medium. it does not heat the medium approximately. heat travels in a straight line.
e g : heat from sun comes without any medium (zero atmosphere) to the earth by radiation.

8.0 flash pint, fire point, ignition temp.

FLASH POINT :      the min tenp at which the rate of vaporization of fuel is sufficient to produce a momentary flash upon the application of source of ignition.

FIRE POINT :     the min temp at which the burning vapor is capable to enable combustion continue.

IGNITION TEMP :    the min temp at which fuel will ignite without help of ignition source. it also called "auto ignition temp".

9.0 source of ignition.

a) spark:
          * friction
          * static charge
          * loose electric connection
          * lightening
          * welding

b) flame
          * match stick
          * gas cutting torch

c) heat of chemical reaction
          *exothermic reaction

d) heat of compression

e) nuclear heat