1. 5
Fire Behavior

2. Objectives (1 of 4) Describe the chemistry of fire.
Define the three states of matter.
Describe how energy and work are interrelated.
Describe the conditions needed for a fire.
Explain the chemistry of combustion.
Describe the products of combustion.

3. Objectives (2 of 4)
Explain how fires can spread by conduction, convection, and radiation.
Describe the four methods of extinguishing fires.
Define Class A, B, C, D, and K fires.
Describe the characteristics of solid-fuel fires.

4. Objectives (3 of 4)
Describe the ignition phase, growth phase, fully developed phase, and decay phase of a fire.
Describe the characteristics of a room-and-contents fire.
Explain the causes and characteristics of flameover, flashover, thermal layering, and backdraft.

5. Objectives (4 of 4) Describe the characteristics of liquid-fuel fires.
Define the characteristics of gas-fuel fires.
Describe the causes and effects of a boiling liquid expanding vapor explosion (BLEVE).
Describe the process of reading smoke.

6. Introduction Fire has been around since the beginning of time.
Destruction of lives and property by uncontrolled fires has occurred since just as long.

7. The Chemistry of Fire
Understanding the conditions needed for a fire to ignite and grow will increase your effectiveness.
Being well trained in fire behavior will allow the fire fighter to control a fire utilizing less water.

8. What Is Fire?
Rapid chemical process that produces heat and usually light
Fire is neither solid nor liquid.
Wood is a solid, gasoline is a liquid, and propane is a gas—but they all burn.

9. Matter
Atoms and molecules
Three states
Solid
Liquid
Gas

10. Solids Definite shape Stokes most uncontrolled fires
Expands when heated and contracts when cooled

11. Liquids Assume the shape of their containers
Most will turn into gases when sufficiently heated
Has a definite volume

12. Gases Have neither independent shape nor volume Expand indefinitely
Mixture of gases in air maintain a constant composition
21% Oxygen
78% Nitrogen
1% Other gases

13. Fuel
Form of energy
Energy released in the form of heat and light has been stored before it is burned

14. Types of Energy
Chemical
Mechanical
Electrical
Light
Nuclear

15. Chemical Energy Energy created by a chemical reaction.
Some of these reactions produce heat and are referred to as exothermic reactions.
Some of these reactions absorb heat and are referred to as endothermic reactions.

16. Mechanical Energy
Converted to heat when two materials rub against each other and create friction
Heat is also produced when mechanical energy is used to compress air in a compressor.

17. Electrical Energy
Produces heat while flowing through a wire or another conductive material
Other examples of electrical energy
Heating elements
Overloaded wires
Electrical arcs
Lightning

18. Light Energy
Caused by electromagnetic waves packaged in discrete bundles called photons
Examples of light energy
Candles
Light bulbs
Lasers

19. Nuclear Energy Created by nuclear fission or fusion
Controlled (nuclear power plant)
Uncontrolled (atomic bomb explosion)
Release radioactive material

20. Conservation of Energy
Energy cannot be created or destroyed by ordinary means.
Energy can be converted from one form to another.
Chemical energy in gasoline is converted to mechanical energy when a car moves along a road.

21. Conditions Needed for Fire
Three basic factors required for combustion:
Fuel
Oxygen
Heat
Chemical chain reactions keep the fire burning.

22. Chemistry of Combustion (1 of 2)
Compounds of atoms and molecules
Almost all fuels are hydrocarbons
Consist of both hydrogen and carbon atoms
Wide variety of other molecules that release toxic by-products
Incomplete combustion produces large quantities of deadly gases

23. Chemistry of Combustion (2 of 2)
Oxidation
Combustion
Pyrolysis

24. Products of Combustion
Combustion produces smoke and heat.
Specific products depend on:
Fuel
Temperature
Amount of oxygen available
Few fires consume all available fuel.

25. Smoke Airborne products of combustion Consists of:
Ashes
Gases
Aerosols
Inhalation of smoke can cause severe injuries.

26. Smoke Contents (1 of 2) Particles Vapors
Solid matter consisting of unburned, partially, or completely burned substances
Vapors
Small droplets of liquids suspended in air
Oils from the fuel or water from suppression efforts

27. Smoke Contents (2 of 2) Gases Most gases produced by fire are toxic.
Common gases include:
Carbon monoxide
Hydrogen cyanide
Phosgene

28. Fire Spread Three methods of fire spread: Conduction Convection
Radiation

29. Conduction
Heat transferred from one molecule to another (direct contact)
Good conductors absorb heat and transfer it throughout the object.

30. Convection Circulatory movement in areas of differing temperatures
Creates convection currents

31. Convection Within a Room
Hot gases rise, then travel along the ceiling.
Convection may carry the fire outside the room of origin

32. Radiation Transfer of heat in the form of an invisible wave
Travels in all directions
Is not seen or felt until it strikes an object and heats its surface

33. Methods of Extinguishment
Cool the burning material.
Exclude oxygen.
Remove fuel.
Break the chemical reaction.

34. Classes of Fire Five classes of fires: Class A Class B Class C Class D
Class K

35. Class A Involve ordinary solid combustibles Cool the fuel with water
Wood
Paper
Cloth
Cool the fuel with water

36. Class B Involve flammable or combustible liquids
Gasoline
Kerosene
Oils
Shut off the fuel supply or use foam to exclude oxygen from the fuel

37. Class C Involve energized electrical equipment
Attacking a Class C fire with an extinguishing agent that conducts electricity can result in injury or death.

38. Class D Involve combustible metals
Sodium
Magnesium
Titanium
The application of water will result in violent explosions
Must be attacked with special agents

39. Class K Involve combustible cooking oils and fats
Special extinguishers are available to handle this type of fire.

40. Solid Fuels Most fires encountered involve solid fuels.
Do not actually burn in the solid state
Must be heated or pyrolyzed to decompose into vapor
May change directly from a solid to a gas
Wood does not have a fixed ignition temperature

41. Solid-Fuel Fire Development
Four distinct phases:
Ignition
Growth
Fully developed
Decay

42. Ignition Phase Fuel, heat, and oxygen are present.
Flame produces a small amount of radiated energy.
Convection and radiation heat the fuel.

43. Growth Phase
Kindling starts to burn, increasing convection of hot gases upward.
Energy radiates in all directions.
Major growth in an upward direction

44. Fully Developed Phase Produces the maximum rate of burning
Fire will burn as long as fuel and oxygen remain.

45. Decay Phase Fuel is nearly exhausted Rate of burning slows
Flames become smoldering embers

46. Key Principles of Solid-Fuel Fire Development (1 of 2)
Hot gases and flame tend to rise.
Convection is the primary factor in spreading the fire upward.
Downward spread occurs primarily from radiation and falling chunks of flaming material.
If there is no remaining fuel, the fire will go out.

47. Key Principles of Solid-Fuel Fire Development (2 of 2)
Variations in the direction of fire spread occur if air currents deflect the flame.
The total material burned reflects the intensity of the heat and the duration of the exposure to the heat.
An adequate supply of oxygen must be available to fuel a free-burning fire.

48. Room Contents
Synthetic products prevalent today made from petroleum products.
These produce dense smoke that can be highly toxic.
Newer paints
Carpets
Furniture

49. Ignition Phase Flame begins small and localized
Convection of hot gases is the primary means of fire growth
Fire could probably be extinguished with a portable fire extinguisher

50. Growth Phase Additional fuel is drawn into the fire.
Convection current carries hot gases to the ceiling
Flames spread upward and outward
Radiation starts to play a greater role
Growth is limited by the fuel and oxygen available

51. Fully Developed Phase Flammable materials are pyrolyzed.
Volatile gases are being released.
Flashover
All combustible materials in a room ignite at once.
Temperatures can reach 1000 °F.
Fire fighters cannot survive for more than a few seconds in a flashover

52. Decay Phase Burning decreases to the point of smoldering fuel
May continue to produce a large volume of toxic gases

53. Special Considerations
Three conditions
Flameover (or rollover)
Thermal layering
Backdraft

54. Flameover (Rollover)
Flaming ignition of hot gases layered in a developing room or compartment fire
Flames can extend throughout the room at the ceiling level

55. Thermal Layering Gases rise and form layers Thermal balance
Water applied to a fire creating steam
Steam displaces hot gases at the top of the room
Ventilate while attacking the fire
Avoid directing water at the ceiling

56. Backdraft (1 of 3) Requires a “closed box”
Explosion that occurs when oxygen is suddenly admitted to a confined area that is very hot and filled with combustible vapors
© Dennis Wetherhold, Jr.

57. Backdraft (2 of 3) Signs of an impending backdraft:
Confined fire with a large heat build-up
Little visible flame from the exterior
“Living fire”
Pressurized smoke
Smoke-stained windows
Turbulent smoke
Ugly yellowish smoke

58. Backdraft (3 of 3) Prevention of backdrafts:
Ventilate at a high level to allow superheated gases to escape before or just as additional oxygen is introduced.
Well-coordinated fire attack

59. Liquid-Fuel Fires (1 of 2)
A liquid must be converted to a gaseous state before it will burn.
Conditions required for ignition:
Fuel–air mixture within flammable limits
An ignition source with sufficient energy
Sustained contact between ignition source and fuel–air mixture

60. Liquid-Fuel Fires (2 of 2)
Flammability is determined by the compound with the lowest ignition temperature
Flash point is the lowest temperature at which vapor is produced
Flame point (or fire point) is the lowest temperature at which sufficient vapors are produced

61. Gas-Fuel Fires (1 of 2) Vapor Density Weight of a gas fuel
Gas with vapor density less than 1 will rise.
Gas with vapor density greater than 1 will settle.
Knowing vapor density helps predict where the danger of ignition will be.

62. Gas-Fuel Fires (2 of 2) Flammability limits
Below the lower flammability limit
Too little fuel = too lean
Above the upper flammability limit
Too much fuel = too rich

63. BLEVE (1 of 2) Boiling liquid, expanding vapor explosion
Occurs when a vessel storing liquid fuel under pressure is heated excessively

64. BLEVE (2 of 2) Vessel is heated.
Internal pressure rises past ability to vent.
Temperature exceeds the boiling point of the liquid causing the vessel to fail.
Liquid immediately turns into a rapidly expanding cloud of vapor.
Vapor ignites into a huge fireball.

65. Smoke Reading (1 of 4)
Enables the fire fighter to learn where the fire is, how big it is, and where it is moving
Fires are dynamic events.
Smoke is the fuel all around you at a fire.
The best place to observe patterns of smoke is outside of the fire building.

66. Smoke Reading (2 of 4) Determining the key attributes of smoke
Smoke volume
Smoke velocity
Smoke density
Smoke color
Black fire

67. Smoke Reading (3 of 4) Determine the influences on the key attributes
Size of the structure
Wind conditions
Thermal balance
Fire streams
Ventilation openings
Sprinkler systems

68. Smoke Reading (4 of 4) Determine the rate of change Predict the event
Changes in the four key attributes indicate changes in the fire
Predict the event
Consider the key attributes, what influences them, and their rate of change
Communicate key parts to the company officer

69. Smoke Reading Through a Door
If smoke exits through the top half and clean air enters through the bottom half
If smoke rises and the opening clears
If smoke thins, but still fills the door

70. Summary (1 of 3)
Characteristics of solids, liquids, and gases are different.
Fire triangle and fire tetrahedron represent conditions necessary for combustion.
Five classes of fire require specific extinguishing methods.

71. Summary (2 of 3) Knowledge of fire spread
Typical fires pass through four distinct phases.
Liquid-fuel fires, gas- fuel fires, and interior fires have unique characteristics.

72. Summary (3 of 3)
Flameover, themal layering, and backdraft are conditions that threaten fire fighters and victims.
Smoke reading enables the fire fighter to learn where the fire is, how big it is, and where it is moving.