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Fire Behavior & Chemistry for Firefighters
A training guide to combustion, fuels, heat, phases of fire, flashover, backdraft and extinguishment theory.
Effective fire control and extinguishment requires a basic understanding of the chemical and physical nature of fire. This includes information describing sources of heat energy, composition and characteristics of fuels, and environmental conditions necessary to sustain the combustion process.
Each lesson explains the science in plain language, then ties it to the fireground with a real incident case file, firefighter terms, study questions, and links to the simulators so you can practice what you read.
The lessons
- Anatomy of Fire & Oxidizing AgentsWhat combustion is, the fire tetrahedron, flaming vs. smoldering fire, oxygen and oxidizers. (6 min)
- Fuels: Solids, Liquids, Gases & Flammable RangePyrolysis, flash point, vapor density, flammable range tables and why modern fuel burns faster. (7 min)
- Sources of Heat EnergyChemical, electrical, mechanical and nuclear heat, and how hidden ignition sources start fires. (4 min)
- Phases of Fire, Flashover & BackdraftFire growth stages, ventilation-limited fires, flashover, rollover, backdraft and smoke explosion. (7 min)
- Heat TransferConduction, convection and radiation, flow path and why a closed door matters. (5 min)
- Products of CombustionFire gases, smoke, heat and flame, and how to protect yourself. (4 min)
- Extinguishment Theory & Classes of FireCooling, smothering, fuel removal, chain-breaking and Class A, B, C, D and K fires. (4 min)
- Fire Behavior GlossaryPlain-language definitions of the terms used throughout the guide, plus fireground slang. (5 min)
Read them in order the first time. Each lesson builds on the one before: the tetrahedron explains fuel, heat and oxygen; those explain how fire develops; and development explains why ventilation, heat transfer and smoke matter so much.
What you will be able to do
- Explain why flaming fire needs four things, and which extinguishing agent attacks which one.
- Read fuel hazards: flash point, vapor density and flammable range.
- Describe the stages of fire growth and recognize ventilation-limited conditions.
- Tell flashover, rollover, backdraft and smoke explosion apart.
- Match heat transfer, smoke and extinguishing agent to the situation in front of you.
How this guide is built
The facts, figures and incident details in these lessons were checked against primary and professional sources, including NIST, UL Firefighter Safety Research Institute, OSHA/NIOSH, NASA and the National Academies. Each lesson lists them at the bottom so you can read the originals. Diagrams were drawn for this site. If you find an error or know a better source, please use the Contact Us button.
This guide is for education. Tactics differ between departments and change as research advances, so always follow your department’s procedures and your officer.
Practice in the simulators
Fire behavior FAQ
What is fire behavior?
Fire behavior is the study of how fires start, grow, spread and decay, and how fuel, heat, oxygen, ventilation and the building itself change what a fire does. Firefighters use it to predict conditions and choose safe, effective tactics.
What is the difference between the fire triangle and the fire tetrahedron?
The fire triangle has three sides: fuel, heat and oxygen. The fire tetrahedron adds a fourth, the uninhibited chemical chain reaction, which sustains flaming combustion. Removing any one side extinguishes the fire.
What is the difference between flashover and backdraft?
Flashover is the transition from a growing fire to a fully developed one, driven by radiant heat igniting everything exposed in a room. Backdraft is a rapid or explosive burn that happens when air reaches a ventilation-limited compartment holding hot, fuel-rich gases.
How fast can flashover happen in a modern home?
In UL Firefighter Safety Research Institute experiments, rooms furnished with modern products reached flashover in under five minutes, while the fastest room with legacy furniture took just over 29 minutes.
Is this guide free?
Yes. All lessons, the glossary and the simulators on Free Fire Simulator are free to use.
About this guide. The Fire Behavior & Chemistry series was originally informed by LBFD Training Division recruit training material. This edition has been independently rewritten and expanded using the sources listed on each page, and its diagrams were drawn for this site. Free Fire Simulator is not affiliated with or endorsed by LBFD. Spotted an error or have a better source? Use the Contact Us button.