Fire Tetrahedron
Definition
The model of sustained combustion requiring four concurrent elements: fuel, oxidiser, heat, and an uninhibited radical chain reaction. Replacing the older fire triangle by adding the chain-reaction element explains why halon agents extinguish fire without cooling or oxygen removal.
- Core elements
- Fuel, oxidiser, heat, chain reaction
- What stops a fire
- Remove or disrupt any one of the four elements
Common questions
What are the four elements of the fire tetrahedron?+
Fuel, oxidiser (oxygen), heat, and an uninhibited chemical chain reaction. All four must be present at the same time for combustion to continue. Remove or disrupt any one and the fire stops.
How is the fire tetrahedron different from the fire triangle?+
The older fire triangle model left out the chemical chain reaction. The tetrahedron adds that fourth element to explain why certain extinguishing agents like halon work without cooling the fire or removing oxygen. They interrupt the radical chain reaction instead.
Why do halon extinguishers work without cooling?+
Halon attacks the uninhibited chemical chain reaction, the fourth side of the tetrahedron. It disrupts that radical chain without needing to remove heat or oxygen. Dry-chemical extinguishers work the same way.
Related terms
- Flashover
- The near-simultaneous ignition of all exposed combustible surfaces in a compartment, occurring when the upper gas layer reaches approximately 600°C and radiative...
- Backdraft
- A deflagration event triggered when air is suddenly admitted to a compartment where a fire has been oxygen-depleted but has continued to...
- Flash Point
- Lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture in air, but the vapour does not...
- NFPA 921
- US National Fire Protection Association Guide for Fire and Explosion Investigations. The internationally accepted methodology Indian fire investigators and SFSL fire divisions...
- V-Pattern
- A V-shaped area of heat and smoke damage on a vertical surface, produced by the upward cone of the fire plume; the...
- Arrhenius Equation
- Mathematical expression relating reaction rate to temperature: k = A × exp(-Ea/RT). The exponential dependence explains the self-accelerating nature of combustion as...
- ASTM E1188
- Standard Practice for Collection and Preservation of Information and Physical Items by a Technical Investigator, the companion evidence-preservation standard to NFPA 921...
- Auto-Ignition Temperature
- The minimum temperature at which a material ignites spontaneously without a pilot flame or spark. Relevant to the assessment of ignition scenarios...
- Carboxyhaemoglobin (COHb)
- The compound formed when carbon monoxide binds to haemoglobin at the oxygen-binding site, with an affinity 200-250 times greater than oxygen. Produces...
- Char Depth Gradient
- The depth of charred wood measured at multiple points; deeper char means longer exposure, so the gradient reveals the direction of fire...
- Conductive Heat Transfer
- Transfer of thermal energy through a solid material by molecular vibration. Rate depends on thermal conductivity, temperature gradient, cross-sectional area, and path...
- Convective Heat Transfer
- Transfer of heat by bulk movement of a fluid (gas or liquid). In compartment fires, the buoyant hot gas plume carries most...
Explained in these topics
- Fire and Arson Investigation: Cause, Origin and Burn PatternsModern model adding a fourth side, the uninhibited chemical chain reaction. Halon and dry-chemical extinguishers attack this fourth side.
- Fire and Burn Pattern InterpretationThe four elements needed for combustion: oxidiser (oxygen), fuel, heat, and an uninhibited chemical chain reaction. Remove any one and the fire stops. Replaces...
- Fire Chemistry: Combustion, Oxidation and the Fire TetrahedronThe four-component model of combustion: fuel, oxidiser, heat, and uninhibited chemical chain reaction. Extinguishment requires removing or disrupting at least...
- Fire Chemistry, Pyrolysis and the Arson Investigation FrameworkThe model of sustained combustion requiring four concurrent elements: fuel, oxidiser, heat, and an uninhibited radical chain reaction. Replacing the older fire...