Lesson 1
Fire Science
In This Lesson
1. Fire Triangle & Tetrahedron
Understanding the elements required for fire is fundamental to fire science and suppression.
Fire Triangle
The three elements needed for fire:
- 🔥Heat: Ignition source; raises material to ignition temperature
- ⛽Fuel: Combustible material in solid, liquid, or gas form
- 💨Oxygen: Air contains ~21% oxygen; fire needs at least 16%
Fire Tetrahedron
Modern understanding adds a fourth element:
- • Heat
- • Fuel
- • Oxygen
- ⚡Chemical Chain Reaction: Self-sustaining reaction that keeps fire burning
Remove any element to extinguish fire.
Key Terms
2. Fire Classification
Fires are classified based on the type of fuel involved. Knowing the class helps determine the appropriate extinguishing agent.
Ordinary Combustibles
Materials: Wood, paper, cloth, rubber, plastics
Extinguishing Agent: Water (cooling method)
Leave ash residue
Flammable Liquids
Materials: Gasoline, oil, grease, solvents, paint
Extinguishing Agent: Foam (AFFF), CO₂, dry chemical
Never use water - spreads fire
Electrical Equipment
Materials: Energized electrical equipment, wiring, panels
Extinguishing Agent: CO₂, dry chemical (non-conductive)
De-energize first if possible, then treat as Class A or B
Combustible Metals
Materials: Magnesium, titanium, sodium, potassium, lithium
Extinguishing Agent: Special dry powder (Met-L-X, G-1)
Water can cause violent reaction
Kitchen/Cooking Fires
Materials: Cooking oils, animal fats, vegetable oils
Extinguishing Agent: Wet chemical (saponification)
Common in commercial kitchens
3. Methods of Heat Transfer
Heat energy moves from warmer to cooler areas through three methods.
Conduction
Heat transfer through direct contact between molecules in solids.
Example: Heat traveling through a metal beam from one end to another
Fire Concern: Fire can spread through building materials, pipes, structural elements
Convection
Heat transfer through movement of fluids (liquids and gases).
Example: Hot air rising and cool air descending (natural convection)
Fire Concern: Fire spreads vertically in buildings through stairwells, shafts, open spaces
Radiation
Heat transfer through electromagnetic waves; no medium required.
Example: Heat from the sun, heat felt from a campfire
Fire Concern: Ignites adjacent structures without direct contact; exposure fires
4. Phases of Fire
Understanding fire phases helps firefighters predict fire behavior and plan tactical operations.
Incipient (Ignition) Phase
- • No visible flame
- • Invisible products of combustion
- • Normal room temperature
- • Smoke detectors may activate
- • Best time for suppression
Growth (Free-Burning) Phase
- • Open flame visible
- • Oxygen being consumed
- • Heat and smoke generated
- • Temperature increasing rapidly
- • Fire grows exponentially
Fully Developed Phase
- • Maximum heat release
- • All combustibles burning
- • Flashover may occur (1000°F/538°C)
- • Most dangerous phase
- • Structural collapse possible
Decay Phase
- • Fuel or oxygen depleted
- • Temperature decreasing
- • Fire intensity reducing
- • Backdraft hazard if ventilation-controlled
- • Overhaul operations begin
⚠️ Critical Phenomena
Flashover
Sudden full-room involvement when heat radiates back and ignites all combustibles simultaneously.
Backdraft
Explosive combustion when oxygen is introduced to a ventilation-limited fire.
5. Combustion Process
Combustion is a chemical reaction between fuel and oxygen that produces heat and light.
Types of Combustion
Complete Combustion
Sufficient oxygen; produces CO₂ and H₂O; clean burning; bright flame
Incomplete Combustion
Limited oxygen; produces CO (carbon monoxide); sooty, smoky; yellow/orange flame
Spontaneous Combustion
Self-heating without external ignition; oxidation generates heat; common with oily rags
Products of Combustion
Flame & Heat
Visible light; thermal energy
Smoke
Solid particles, gases; reduces visibility
Carbon Dioxide (CO₂)
Displaces oxygen; asphyxiant
Carbon Monoxide (CO)
Colorless, odorless; deadly poison
BFP Fire Science Tips
- ✓Memorize fire classes - know materials and extinguishing agents for each class.
- ✓Understand fire phases - recognize indicators and hazards at each stage.
- ✓Learn heat transfer methods - understand how fire spreads in structures.
- ✓Know flashover & backdraft - these are critical safety concepts.