1.2 Fire Behavior and Heat Transfer
Key Takeaways
- The fire tetrahedron requires fuel, heat, oxygen, and a sustained chemical chain reaction.
- Heat transfer questions usually turn on conduction, convection, radiation, and direct flame contact.
- Rollover, flashover, backdraft, and ventilation-limited fire growth are related fire behavior clues.
- Modern fire-dynamics answers emphasize flow-path control, coordinated ventilation, and effective water application.
Fire as a system
A working fire is controlled by the fire tetrahedron: fuel, heat, oxygen, and the chemical chain reaction. Extinguishment works by removing or limiting one side of that tetrahedron. Cooling removes heat, smothering limits oxygen, fuel control removes what can burn, and some agents interrupt the chain reaction.
Exam questions often describe a scene instead of naming the concept. Smoke banking down a hallway, flames rolling in the upper gas layer, or a door opening that changes fire intensity are all clues about how heat and gases are moving.
| Heat-transfer method | What moves heat | Common clue |
|---|---|---|
| Conduction | Direct transfer through a solid | Heat travels through metal, pipe, or structural members |
| Convection | Movement of hot gases or liquids | Heat and smoke rise through stairs, shafts, or voids |
| Radiation | Energy across space | Nearby contents heat without direct contact |
| Direct flame contact | Flame touches exposed fuel | Fire extends to curtains, trim, furniture, or contents |
Compartment fire behavior
A compartment fire may begin as a small, fuel-controlled fire and then enter a growth stage as heat releases more flammable vapors. Rollover occurs when unburned gases ignite in the upper layer. Flashover is the rapid transition where exposed combustibles in the space ignite. Backdraft is associated with a ventilation-limited fire that has hot gases and unburned products waiting for oxygen.
The exam pattern is usually practical: what changed? Did someone open a door, break a window, ventilate above the fire, or apply water? Modern fire dynamics emphasizes the flow path, meaning the route heat and smoke take from the fire area toward an exhaust opening.
Use this checklist in scenarios:
- Identify what is burning and what class or fuel package it suggests.
- Track where heat, smoke, and gases are moving.
- Decide whether ventilation has increased or decreased.
- Choose the action that removes heat, limits oxygen, controls fuel, or interrupts the chain reaction.
A closed fire apartment has dark smoke pushing under pressure around the door. Why would the officer assign door control while the line is charged?