1. Chapter 4
Fire Behavior

2. Introduction
Since ancient times, fires has been one of the most important life-sustaining components
Fire has played a major role as a tool in the development of society
Sometimes an ally, sometimes an enemy
Much has been learned about fire in the last thirty years

3. Fire Defined Fire is burning
Burning is combustion
Combustion is a chemical reaction
Deflagration is combustion at a rate below the speed of sound
Detonation is combustion above the speed of sound
Fire tetrahedron is the assembly of heat, fuel, oxygen, and a self-sustaining chemical reaction

4. Figure 4-2 The old and new ways of visualizing the combustion process: the fire triangle and the fire tetrahedron.

5. Figure 4-3 An exothermic reaction.

6. Heat For a fire to begin, fuels need to be heated
Chemical heat: various chemicals react with each other
Mechanical heat: friction of two materials rubbing against each other
Electricity most recognized source of heat
Nuclear heat comes from unstable radioactive materials

7. Figure 4-5 Heat from friction can be produced whenever any rubbing or compression occurs.

8. Figure 4-6 Electricity is simply a flow of electrons from a place where there are many to a place where they are lacking.

9. Figure 4-7 The process of creating nuclear energy and heat.

10. Fuel Material consumed by the combustion process
Molecules in a solid are packed closely together
Liquid’s ability to burn depends on substance's ability to place its molecules into suspension
Gaseous fuels are in a state of suspension
Primed for combustion
Fuel must be at a certain temperature before combustion can take place

11. Figure 4-8 States of matter
Figure 4-8 States of matter. Solid materials have dense arrangements of molecules whereas gaseous molecules are more free-flowing.

12. Oxygen Acts as a catalyst for the combustion process
Oxidation is the process of oxygen bonding to other elements and compounds
Oxidation affects the process of combustion
Chemical reaction accelerated with an abundance of oxygen

13. Figure 4-11 The speed of combustion is affected by the amount of oxygen present.

14. Chemical Chain Reaction
When heat, fuel, and oxygen combine to start combustion, a chemical chain reaction forms
Scientists discovered certain chemicals introduced into burning process can stop flaming
Foundation for understanding how fires begin is grounded in the fire tetrahedron

15. Fire Growth
Once a fire begins, it will grow in a self-sustaining manner
The heat being released will be transferred to other fuels
The firefighter who understands fire growth can better predict fire behavior

16. Modes of Heat Transfer Heat is a by-product of combustion
Conduction is the transfer of heat through a solid object
Convection is the transfer of heat through air and liquid currents
Radiation is the transfer of heat through invisible lightwaves

17. Figure 4-12 Examples of heat transfer in fire.

18. Figure 4-14 A natural fire plume in an unrestricted space.

19. (A)
(B)
Figure (A) Radiation, single heat source. (B) Radiation, multiple heat sources.

20. Fire Phases Burning occurs in clearly defined phases
Ignition phase: substance begins to heat up, liberates gases that can burn
Growth phase: fire begins to grow from the point of ignition
Fully developed phase: all contents within perimeter of fire's boundaries are burning
Decay stage: all fuel consumed and the fire diminishes in size

21. Figure 4-17 The four phases of fire.

22. Figure 4-19 Full involvement of a structure is an example of a fully-developed-phase fire.

23. Products of Combustion
Matter is neither lost nor gained; it changes form
By-products of burning process are heat, light, and smoke
Heat causes dehydration, heat exhaustion, and burns
Light can cause damage to eyesight
Smoke is the most dangerous product of combustion

24. Figure 4-21 The products of combustion are deadly and include light, heat, and smoke.

25. Specific Fire Characteristics and Events
Liquid, electrical, and metal fires have certain characteristics
Several unique fire events can occur within a compartment or structure
Learning to “read smoke” can help predict fire behavior

26. Liquid Fires Liquid fuels must vaporize
Vaporization is the process in which liquids are converted to gas or vapor
Most liquid fires do not mix well with water
Typically extinguished by coating the liquid with an agent such as foam
Liquid heated to a high pressure in a closed vessel can explode
BLEVE (boiling liquid expanding vapor explosion)

27. Figure 4-23 A boiling liquid vapor explosion (BLEVE).

28. Electrical Fires Class C fire: electrical energy is creating heat
Control of a Class C fires begins with control of electricity
Fire control efforts are aimed toward Class A or B materials
Use of water can present extreme shock hazards while fire is still electrically energized

29. Metal Fires Class D metal fire is a chemical reaction fire
In some cases, the presence of water will cause a violent reaction
Control of Class D fires can be quite difficult or amazingly simple
Shape, size, amount, and type of metal burning will dictate the best extinguishment method

30. Hostile Fire Events
Any uncontrolled fire in a building is a hostile fire event
Hostile fire event: unique fire phenomenon
Flashover
Backdraft
Rapid fire spread

31. Reading Smoke at Structural Fires
Firefighter applies understanding of basic fire behavior by reading smoke
Helps discover clues about the location of the fire
Smoke volume is an indicator of the amount of fuels that are “off-gassing”
Smoke velocity is an indicator of pressure that has built up within the building
Smoke density is indicative of the amount of fuel that is laden within the smoke

32. Figure Smoke leaving a building has four attributes: volume, velocity, density, and color. (Photo by Keith Muratori from FIREGROUNDIMAGES.com)

33. Figure Turbulent smoke flow is a warning sign of impending flashover. The brown smoke issuing from the eves indicates that the roof trusses have been heated—a collapse warning sign. (Photo by Keith Muratori from FIREGROUNDIMAGES .com)

34. Table 4-3 Reading Smoke Shortcuts

35. Lessons Learned
Firefighter survival and fire attack effectiveness is dependent on the understanding of fire dynamics
Ingredients needed for combustion
Heat sources
Fuels
Fire phases
Special considerations
Reading smoke