6. Heat
For a Fire to Start,
there must be a heat or
ignition source
7. TOGETHER, THEY PRODUCE A
CHEMICAL CHAIN REACTION
THAT IS FIRE,
which produces
heat and light.
8.
9. Types of Fires
Fires Are Classified
by the type FUEL
they burn.
The 4 Types are
❑A
❑B
❑C
❑D
10. Class A Fires (Carbonaceous)
Wood,
Paper,
Plastic,
Rags, etc
Combustible
Material burn and
ash is left behind
11. Class B Fires (Oil)
Gasoline,
Oil,
Grease,
Paint, etc
Water not to be
used as oil is
lighter and will
float
12. Class C Fires
Electrical Fires and
Gases under fire
Office Equipment,
Motors,
Switchgear,
Heaters,
Gases
ELECTRICITY ITSELF DOES NOT BURN.
IT PROVIDES THE IGNITION TO START A FIRE
18. ATOMS AND MOLECULES
➢SMALLEST PART OF A SUBSTANCE
WHICH CAN TAKE PART IN A CHEMICAL
REACTION IS CALLED AN ATOM
➢SMALLEST PART OS A SUBSTANCE
WHICH CAN EXIST FREELY IS CALLED A
MOLECULE
19. CHEMICAL REACTION
❖WHEN TWO OR MORE SUBSTANCES
COMBINE TOGETHER TO FORM A
NEW SUBSTANCE OR
SUBSTANCES, IT IS CALLED A
CHEMICAL REACTION
20. ➢A REACTION PRODUCES ENERGY, IE
HEAT IS CALLED EXOTHERM
REACTION
FIRE IS AN EXOTHERM REATION BETWEEN
FUEL AND OXYGEN.
NEXT TO HEAT, A FIRE GENERALLY
PRODUCES LIGHT, COMBUSTION GASES AND
SOOT.
EXOTHERM REACTION
21. ➢TO INITIATE A FIRE A CERTAIN AMOUNT OF
ENERGY IS NEEDED.
TAKE A EXAMPLE OF A SIMPLE TEST WITH GASOLINE
AND DIESEL FUEL. A MATCH HAS ENOUGH ENERGY TO
LIGHT THE GASOLINE BUT IN THE DIESEL FUEL THE
MATCH EXTINGUISHES.
➢IN CHEMISTRY THE ENERGY NEEDED TO
START A REACTION IS CALLED THE
ACTIVATION ENERGY.
ACTIVATION ENERGY
22. CHAIN REACTION
➢CHEMICAL REACTIONS NEEDS TO SURMOUNT
ACTIVATION ENERGY BEFORE THE REACTION CAN
TAKE PLACE .
➢IN A FIRE, THE INITIAL ENERGY SOURCES THAT
CAUSE THE FIRE CAN BE MULTIPLE, E.G. A SPARK,
AN OPEN FLAME, ELECTRICITY, SUNLIGHT, ETC
➢ONCE THE REACTION IS STARTED, HOWEVER, IT
GENERATES MORE THAN ENOUGH ENERGY TO BE
SELF-SUSTAINING, A CHAIN REACTION OCCURS.
THE ENERGY GIVEN OFF IN EXCESS CAN BE SEEN
AS LIGHT AND HEAT GENERATED BY THE FIRE.
23. PYROLYSIS
➢THE ENERGY LIBERATED IN THE
COMBUSTION PROCESS CAUSES THE
CHEMICAL COMPOSITION OF THE FUEL TO
BREAK DOWN INTO SMALL MOLECULES
➢ THIS PROCESS IS CALLED PYROLYSIS
THE PYROLYSIS PROCESS CAUSES THE
EVAPORATION OF THE FUEL
24. MOLECULES EVAPORATE AND REACT WITH
THE OXYGEN IN THE AIR.
➢COMPLETE COMBUSTION MEANS THAT
JUST ENOUGH OXYGEN MOLECULES
ARE PRESENT, TO OXIDISE THE FUEL
MOLECULES.
COMPLETE REACTION
25. CATALYST
➢CATALYST HAS THE OPPOSITE EFFECT OF AN
INHIBITOR
➢CATALYST IS A SUBSTANCE, WHICH PROMOTES
THE REACTION (WITHOUT BEING ALTERED OR
USED IN THE REACTION)
E.G. ADDING METAL SHAVINGS TO OIL RAGS AIDS
THEIR COMBUSTION
26. THE IGNITION TEMPERATURE OF A
SUBSTANCE (SOLID, LIQUID OR GASEOUS)
IS THE MINIMUM TEMPERATURE TO WHICH
THE SUBSTANCE EXPOSED TO AIR MUST BE
HEATED IN ORDER TO CAUSE COMBUSTION
OR FIRE
IGNITION TEMPERATURE
27. ➢THE LOWEST TEMPERATURE AT WHICH A
SUBSTANCE CONTINUES TO BURN IS
(USUALLY A FEW DEGREES ABOVE ITS
FLASHPOINT) AND IS CALLED FIRE POINT
OR FLASH POINT
A SPECIFIC IGNITION TEMPERATURE FOR SOLIDS
IS DIFFICULT TO DETERMINE BECAUSE THIS
EPENDS UPON MULTIPLE ASPECTS SUCH AS
HUMIDITY (WET WOOD VERSUS DRY WOOD),
COMPOSITION (TREATED OR NON-TREATED
WOOD) AND PHYSICAL FORM
FIRE OR FLASH POINT
29. • FIRE SPREADS QUICKLY &
GEOMETRICALLY
• RELEASED HEAT INCREASES
TEMPERATURE IN THE VICINITY
• HIGH TEMPERATURE CAUSES
SELF IGNITION IN OTHER FUELS
FIRE SPREAD
30. FIRE SPREAD
THE HEAT LIBERATED BY THE FIRE ALSO CAUSES
THE SURROUNDING MATERIALS TO WARM UP. THE
HEAT TRANSFER IS ACCOMPLISHED BY THREE
MEANS, USUALLY SIMULTANEOUSLY:
✓CONDUCTION
✓CONVECTION
✓RADIATION
31. CONDUCTION
• DIRECT THERMAL ENERGY TRANSFER
DUE TO CONTACT.
• MATERIALS CONDUCT HEAT AT VARYING
RATES. METALS ARE VERY GOOD
CONDUCTORS WHILE CONCRETE AND
PLASTICS ARE VERY POOR CONDUCTORS,
HENCE GOOD INSULATORS
• NEVERTHELESS A FIRE IN ONE SIDEWALL
OF A COMPARTMENT WILL RESULT IN THE
TRANSFER OF HEAT TO THE OTHER SIDE
OF THE WALL.
32. CONVECTION
• HEAT
. TRANSFER THROUGH A LIQUID OR
GAS
• CAUSED BY DENSITY DIFFERENCE OF
THE HOT MOLECULES COMPARED TO
THE COLD ONES (eg. BOILING WATER)
• HOT AIR, GASES EXPAND AND RISE.
• CONVECTION NORMALLY DETERMINES
THE GENERAL DIRECTION OF THE
FIRESPREAD.
• CONVECTION CAUSES FIRES TO RISE AS
HEAT RISES
33. RADIATION
• ELECTROMAGNETIC WAVE TRANSFER OF
HEAT TO AN OBJECT.
• WAVES TRAVEL IN ALL DIRECTIONS
FROM THE FIRE AND MAY BE REFLECTED
OR ABSORBED BY A SURFACE.
• ABSORBED HEAT RAISES THE
TEMPERATURE OF THE MATERIAL
BEYOND ITS IGNITION POINT, CAUSING
IT TO IGNITE.
