The document discusses the chemistry of fire, including the fire triangle of oxygen, fuel, and heat required to start a fire. It explains the four classes of fires based on the type of fuel (A, B, C, D) and defines key terms like pyrolysis, combustion, activation energy, and chain reaction. Fire spread occurs primarily through conduction, convection and radiation. As the fire grows, it can lead to a flashover where the flames spread rapidly to involve the entire compartment.

2. THE CHEMISTRY
OF FIRE

3. Fire Triangle
Fires Require
 Air (oxygen)
Fuel
Heat

4. Air
Air is required as a catalyst
Can be oxygen from the air
OR
From the Fuel itself

5. Fuel
For a fire to start
there must be
something to Burn

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.

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

13. Class D Fires
Metals
 Potassium
 Sodium
 Aluminum
 Magnesium

15. PRODUCTS OF FIRE
 SMOKE
 HEAT
 GASES
 FLAME

16. BY- PRODUCTS OF FIRE
1. Smoke
• Carbon Di Oxide
• Carbon Mono Oxide
• Hydrogen Cyanide
• Hydrogen Chloride
• Unburnt Carbon Particles
2. Heat - Burn and other physical effects
3. Flames
4. Sound
5. Pressure
• Effect on ears and other limbs
}During Explosion

17. TERMS & DIFINITIONS

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. EXOTHERM REACTION
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.

21. ACTIVATION ENERGY
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.

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. COMPLETE REACTION
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.

25. REACTION SURFACE
NEXT TO FUEL, OXYGEN AND ENERGY ONE
SHOULD ALSO NOTE THE MIXING RATIO BETWEEN
OXYGEN AND FUEL.
EXAMPLE, A LOG OF WOOD WILL NOT SUSTAIN A
FIRE IF IT IS LIT WITH A MATCH. AN AMOUNT OF
WOOD SHAVINGS WILL BECAUSE THIS CAUSES A
BETTER MIXTURE BETWEEN FUEL AND AIR,
WHICH FAVORS COMBUSTION.
 LARGER SURFACE OF THE FUEL IN CONTACT
WITH THE AIR CAUSES A GREATER REACTION
SURFACE , WHICH FACOURS COMBUSTION

26. INHIBITOR
IN A FIRE A CHEMICAL CHAIN REACTION OCCURS,
RADICALS OF FUEL REACT WITH RADICALS OF
OXYGEN HEAT AND COMBUSTION PRODUCTS ARE
FORMED.
 ADDING A CHEMICAL MOLECULE, WHICH REACTS
WITH THOSE RADICALS WITHOUT SUSTAINING THE
COMBUSTION PROCESS CAN STOP THE FIRE. THIS
CHEMICAL IS CALLED INHIBITOR
THIS PRINCIPLE IS USED IN DRY CHEMICAL
EXTINGUISHERS WICH CONTAIN E.G. POTASSIUM OR
SODIUM BICARBONATE OR IN THE NOW BANNED
HALON EXTINGUISHERS

27. 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

28. IGNITION TEMPERATURE
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

29. FIRE OR FLASH POINT
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

30. AUTO IGNITION TEMPERATURE
 AUTO-IGNITION TEMPERATURE IS THE LOWEST
TEMPERATURE AT WHICH POINT A SOLID, LIQUID
OR GAS WILL SELF-IGNITE WITHOUT AN IGNITION
SOURCE.
AUTO IGNITION TEMPERATURE OF SUBSTANCES
EXCEEDS ITS FLASHPOINT.
SUCH CONDITIONS CAN OCCUR DUE TO EXTERNAL HEATING -
A FRYING PAN THAT OVERHEATS CAUSING THE OIL TO
AUTOIGNITE, AN EXHAUST-PIPE FROM A CAR DRIVING OVER
DRY GRASS OR STRAW CAN CAUSE IT TO AUTO-IGNITE- OR
THEY CAN OCCUR DUE TO CHEMICAL OR BIOLOGICAL
PROCESSES - A SILO FIRE CAN OCCUR BECAUSE OF THE
BIOLOGICAL PROCESSES IN HUMID ORGANIC MATERIAL.

31. VOLATILITY
VOLATILITY IS HOW READILY A LIQUID
WILL EVAPORATE.
THE VOLATILITY OF A SUBSTANCE IS
CLOSELY LINKED TO ITS BOILING POINT.
THE HIGHER THE BOILING POINT OF A
LIQUID THE HARDER IT WILL BE FOR THE
LIQUID TO EVAPORATE.
THE LOWER THE BOILING POINT, THE
GREATER THE FIRE RISK.

32. DEFLAGRATIONN & DETONATION
THE FEROCITY OF AN EXPLOSION
DEPENDS ON THE SPEED OF THE FLAME
IF THE FLAME SPREAD REMAINS LOWER
THAN 340 M/S THE EXPLOSION IS CALLED A
DEFLAGRATION.
IF THIS SPEED EXCEEDS 340 M/S -AND THEY
CAN REACH UP TO 1800 TO 2000 M/S- IT IS
CALLED DETONATION.
THE DIFFERENCE IS BEING FASTER OR SLOWER
THAN THE SPEED OF SOUND, SUPERSONIC AND
SUBSONIC.

33. FLASHOVER
IN A COMPARTMENT FIRE THERE CAN COME A
STAGE WHERE THE TOTAL THERMAL RADIATION
FROM THE FIRE PLUME, HOT GASES AND HOT
COMPARTMENT BOUNDARIES CAUSES THE
GENERATION OF FLAMMABLE PRODUCTS OF
PYROLYSIS FROM ALL EXPOSED COMBUSTIBLE
SURFACES WITHIN THE COMPARTMENT.
GIVEN A SOURCE OF IGNITION, THIS WILL RESULT IN
THE SUDDEN AND SUSTAINED TRANSITION OF A
GROWING FIRE TO A FULLY DEVELOPED FIRE.......
THIS IS CALLED 'FLASHOVER'......'
MAIN FEATURE OF A 'FLASHOVER' IS THAT THERE IS
TRANSITION TO A STATE OF TOTAL FIRE

34. A TIME COMES WHEN THE FLAMES
CEASE TO BE LOCALISED AND
SPREADS TO THE WHOLE
COMPARTMENT VOLUME.
FIRE CHANGES FROM A SURFACE
PHENOMENON TO A VOLUME
PROCESS

35. BACKDRAFT
LIMITED VENTILATION CAN LEAD TO A FIRE IN A
COMPARTMENT PRODUCING FIRE GASES,
CONTAINING SIGNIFICANT PROPORTIONS OF
PARTIAL COMBUSTION PRODUCTS AND UNBURNT
PYRO LYSIS PRODUCTS (UNDER-VENTILATED FIRE).
IF THESE ACCUMULATE, THEN THE ADMISSION OF
AIR WHEN AN OPENING IS MADE TO THE
COMPARTMENT CAN LEAD TO A SUDDEN INCREASE
OF THE FIRE.
THIS INCREASE IN FIRE, MOVING THROUGH THE
COMPARTMENT AND OUT OF THE OPENING, IS
CALLED BACKDRAFT

37. FIRE SPREAD

38. FIRE SPREAD
• FIRE SPREADS QUICKLY &
GEOMETRICALLY
• RELEASED HEAT INCREASES
TEMPERATURE IN THE VICINITY
• HIGH TEMPERATURE CAUSES
SELF IGNITION IN OTHER FUELS

39. 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

40. 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.

41. 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

42. 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.

43. FIRE SPREAD- CUBE MODEL
HIGHEST DANGER
LESS LESS
DANGER DANGER
LEAST DANGER

44. STAGES OF COMBUSTION

45. FACTORS AFFECTING FIRE
DEVELOPMENT
 PROVIDING THAT THERE IS SUFFICIENT FUEL
AND OXYGEN AVAILABLE THE FIRE MAY TOTALLY
INVOLVE THE COMPARTMENT.
 THE ITEMS FIRST IGNITED IS SUFFICIENTLY
FLAMMABLE TO ALLOW FLAME SPREAD OVER ITS
SURFACES.
 THE HEAT FLUX FROM THE FIRST FUEL
PACKAGE.
IS SUFFICIENT TO IRRADIATE ADJACENT FUEL
PACKAGES WHICH IN TURN WILL BEGIN TO BURN.
 SUFFICIENT FUEL EXISTS.
 OPEN OR WELL-SEALED COMPARTMENT.

46. FLASH OVER
A TIME COMES WHEN THE FLAMES
CEASE TO BE LOCALISED AND
SPREADS TO THE WHOLE
COMPARTMENT VOLUME.
FIRE CHANGES FROM A SURFACE
PHEMENON TO A VOLUME PROCESS

47. FLASHOVER
FLASH
OVER