Chapter 3 Fire Behaviour 1
Introduction Fire has been one of the most important life-sustaining components. Fire a major tool in the development of society Sometimes ally; sometimes enemy To understand fire behaviour: Understanding of fire dynamics Supervised experience and first-hand observations Ongoing commitment to learn 2
Fire Defined Fire Combustion Chemical reaction Deflagration Detonation 3
Fire Tetrahedron Assembly of heat, fuel, oxygen, and a self- sustaining chemical reaction Removal of any one of the four ingredients is the key to fire extinguishment. Cooling the burning material Removing the fuel Excluding oxygen from the fire. Breaking the self-sustaining chemical reaction 4
The old and new ways of visualizing the combustion process: the fire triangle and the fire tetrahedron 5
Heat For a fire to begin, fuels need to be heated. Chemical heat Exothermic and endothermic reaction Mechanical heat Friction of two materials rubbing Electrical heat Most recognized source of heat Nuclear heat Unstable radioactive materials 6
Exothermic reaction Endothermic reaction 7
Heat from friction can be produced whenever any rubbing or compression occurs. 8
Electricity is simply a flow of electrons from a place where there are many to a place where they are lacking. 9
The process of creating nuclear energy and heat 10
Fuel Material consumed by combustion process Solids molecules packed closely together Pyrolysis Liquid’s ability to burn Gaseous fuels in a state of suspension Fuel must be at a certain temperature and certain mixture in air before combustion can take place. Flashpoint Fire point Ignition temperature 11
States of matter. Solid materials have dense arrangements of molecules whereas gaseous molecules are more free-flowing. 12
Oxygen Catalyst for the combustion process Oxidation is the process of oxygen bonding to other elements and compounds. Affects the process of combustion Accelerates chemical reaction 13
The speed of combustion is affected by the amount of oxygen present. 14
Chemical Chain Reaction Heat, fuel, and oxygen combine to start combustion. Certain chemicals 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 released will transfer to other fuels. Understanding fire growth can better predict fire behaviour. 16
A natural fire plume in an unrestricted space. 17
Modes of Heat Transfer Heat is a by-product of combustion. Conduction Convection Radiation 18
(A) Radiation, single heat source (B) Radiation, multiple heat sources 19
Fire Phases Burning occurs in clearly defined phases: Ignition phase Growth phase Fully developed phase Decay stage Thermal layering is the stratification of air and fire gases into layers based on their temperatures. 20
The four phases of fire. 21
Full involvement of a structure is an example of a fully developed phase fire. 22
Products of Combustion Matter changes form By-products: Heat: Dehydration, heat exhaustion, and burns Light Damage to eyesight Smoke Most dangerous product of combustion Considered a by product of incomplete combustion 23
The products of combustion are deadly and include light, heat, and smoke. 24
Specific Fire Characteristics and Events Liquid fires Vapourization Electrical fires Metal fires Hostile fire event Flashover Backdraft Rapid fire spread 25
Reading Smoke at Structural Fires Understanding fire behaviour by reading smoke Smoke volume Amount of fuels that are “off-gassing” Smoke velocity Pressure that has built up Smoke density Amount of fuel that is laden Smoke colour Type of material burning, stage, location 26
Reading Smoke Shortcuts 27
Smoke leaving a building has four attributes: volume, velocity, density, and colour. (Photo by Keith Muratori from FIREGROUNDIMAGES.com) 28
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 29