Key Formulas & Equations
Fire Triangle/Tetrahedron: Fuel + Heat + Oxidizer (+ Chemical Chain Reaction) = Fire
Remove any element = extinguishment
Remove any element = extinguishment
Flash Point: Minimum temperature at which a liquid produces sufficient vapor to form an ignitable mixture with air.
Fire Point: Temperature at which sustained combustion occurs.
Fire Point: Temperature at which sustained combustion occurs.
f⁴ − Tobj⁴) (radiation)
σ = Stefan-Boltzmann constant (5.67×10⁻⁸ W/m²K⁴)
σ = Stefan-Boltzmann constant (5.67×10⁻⁸ W/m²K⁴)
Core Concepts
1. Fire Behavior and Dynamics
Flashover: simultaneous ignition of all exposed combustible surfaces when compartment temperature reaches ~500-600°C. Backdraft: explosive reignition when oxygen is introduced to a superheated, oxygen-depleted compartment. Understanding these phenomena is critical for firefighter safety.
Flashover: simultaneous ignition of all exposed combustible surfaces when compartment temperature reaches ~500-600°C. Backdraft: explosive reignition when oxygen is introduced to a superheated, oxygen-depleted compartment. Understanding these phenomena is critical for firefighter safety.
2. Fire Prevention and Code
NFPA (National Fire Protection Association) codes: life safety (NFPA 101), fire alarms (NFPA 72), sprinklers (NFPA 13). Building design: fire-rated construction, compartmentation, means of egress, fire detection/suppression systems.
NFPA (National Fire Protection Association) codes: life safety (NFPA 101), fire alarms (NFPA 72), sprinklers (NFPA 13). Building design: fire-rated construction, compartmentation, means of egress, fire detection/suppression systems.
3. Fire Suppression Methods
Water (most common, cools and smothers). Foam (Class B fires, suppresses vapors). Dry chemical (interrupts chain reaction). CO₂ (displaces oxygen, leaves no residue). Clean agents (FM-200, Novec 1230 — for sensitive equipment). Wet chemical (kitchen fires).
Water (most common, cools and smothers). Foam (Class B fires, suppresses vapors). Dry chemical (interrupts chain reaction). CO₂ (displaces oxygen, leaves no residue). Clean agents (FM-200, Novec 1230 — for sensitive equipment). Wet chemical (kitchen fires).
4. Fire Investigation
Determine origin (where fire started) and cause (what ignited it). Patterns: V-pattern (fire spreads upward), char depth (indicates fire intensity), spalling (concrete). Causes: accidental, natural, incendiary, undetermined.
Determine origin (where fire started) and cause (what ignited it). Patterns: V-pattern (fire spreads upward), char depth (indicates fire intensity), spalling (concrete). Causes: accidental, natural, incendiary, undetermined.
5. Wildland Fire Science
Fuel types (grass, brush, timber), topography (slope, aspect), weather (wind, humidity, temperature). Fire behavior: surface fire, crown fire, spotting. Fire management: prescribed burns, fuel breaks, defensible space, community wildfire protection plans (CWPP).
Fuel types (grass, brush, timber), topography (slope, aspect), weather (wind, humidity, temperature). Fire behavior: surface fire, crown fire, spotting. Fire management: prescribed burns, fuel breaks, defensible space, community wildfire protection plans (CWPP).
Core Definitions
Flashover: The simultaneous ignition of all exposed combustible surfaces in an enclosed compartment, occurring when the average upper layer temperature reaches 500-600°C. Radiant heat flux at floor level reaches 20 kW/m². Often fatal to occupants and firefighters inside.
Class A/B/C/D/K Fires: A: ordinary combustibles (wood, paper). B: flammable liquids (gasoline, oil). C: energized electrical equipment. D: combustible metals (magnesium, titanium). K: cooking oils/fats.
Fire Load: The total heat energy that would be released per unit area if all combustible materials in a compartment burned. Measured in MJ/m². Determines fire severity and structural fire resistance requirements.
Worked Examples
Example 1: Heat Flux Calculation
Fire at 800°C, object at 20°C, emissivity = 0.9:
q" = 0.9 × 5.67×10⁻⁸ × (1073⁴ − 293⁴) = 0.9 × 5.67×10⁻⁸ × (1.33×10¹² − 7.37×10⁹) ≈ 65.7 kW/m²
Ignition of wood occurs at ~12-25 kW/m² — this flux would ignite nearby combustibles.
Fire at 800°C, object at 20°C, emissivity = 0.9:
q" = 0.9 × 5.67×10⁻⁸ × (1073⁴ − 293⁴) = 0.9 × 5.67×10⁻⁸ × (1.33×10¹² − 7.37×10⁹) ≈ 65.7 kW/m²
Ignition of wood occurs at ~12-25 kW/m² — this flux would ignite nearby combustibles.
Example 2: Smoke Filling Time
Compartment: 50 m² × 3 m = 150 m³. Vent: 1 m × 0.5 m = 0.5 m², velocity 0.5 m/s.
V = 0.5 × 0.5 × t = 0.25t m³. To fill 150 m³: t = 150/0.25 = 600 seconds (10 minutes) to full smoke logging.
Compartment: 50 m² × 3 m = 150 m³. Vent: 1 m × 0.5 m = 0.5 m², velocity 0.5 m/s.
V = 0.5 × 0.5 × t = 0.25t m³. To fill 150 m³: t = 150/0.25 = 600 seconds (10 minutes) to full smoke logging.
Example 3: Fire Investigation
V-pattern on wall, char depth 2 cm on floor joists, spalling on concrete, no accelerant detected. Origin at base of V (point of lowest burning). Cause: electrical short (found melted copper conductor). Classification: accidental (electrical malfunction).
V-pattern on wall, char depth 2 cm on floor joists, spalling on concrete, no accelerant detected. Origin at base of V (point of lowest burning). Cause: electrical short (found melted copper conductor). Classification: accidental (electrical malfunction).
Practice Problems
Problem 1: What are the four components of the fire tetrahedron?
Answer: Fuel, heat (ignition source), oxidizer (oxygen), and chemical chain reaction. Removing any one element extinguishes the fire.
Answer: Fuel, heat (ignition source), oxidizer (oxygen), and chemical chain reaction. Removing any one element extinguishes the fire.
Problem 2: Differentiate flash point and fire point.
Answer: Flash point: minimum temperature producing sufficient vapor for momentary ignition (flash) when exposed to an ignition source. Fire point: minimum temperature at which sustained combustion continues after ignition. Fire point is typically 5-20°C higher.
Answer: Flash point: minimum temperature producing sufficient vapor for momentary ignition (flash) when exposed to an ignition source. Fire point: minimum temperature at which sustained combustion continues after ignition. Fire point is typically 5-20°C higher.
Problem 3: What are the five classes of fire and appropriate extinguishing agents?
Answer: A (wood/paper): water, foam. B (flammable liquids): foam, CO₂, dry chemical. C (electrical): CO₂, dry chemical. D (combustible metals): dry powder (specialized). K (cooking oils): wet chemical.
Answer: A (wood/paper): water, foam. B (flammable liquids): foam, CO₂, dry chemical. C (electrical): CO₂, dry chemical. D (combustible metals): dry powder (specialized). K (cooking oils): wet chemical.
Problem 4: What percentage of fire deaths result from smoke inhalation?
Answer: Approximately 50-80% of fire deaths are caused by smoke inhalation (carbon monoxide poisoning, hydrogen cyanide), not by burns. This is why smoke detectors and closed doors are critical life safety measures.
Answer: Approximately 50-80% of fire deaths are caused by smoke inhalation (carbon monoxide poisoning, hydrogen cyanide), not by burns. This is why smoke detectors and closed doors are critical life safety measures.
Problem 5: What is the difference between a backdraft and a flashover?
Answer: Flashover: simultaneous ignition of all exposed surfaces due to radiant heat (500-600°C). Backdraft: explosive reignition of superheated gases when oxygen is introduced to a starved fire. Both are lethal; backdraft is a sudden explosive event.
Answer: Flashover: simultaneous ignition of all exposed surfaces due to radiant heat (500-600°C). Backdraft: explosive reignition of superheated gases when oxygen is introduced to a starved fire. Both are lethal; backdraft is a sudden explosive event.