Flash Point
Definition
Lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture in air, but the vapour does not sustain combustion. Petrol about minus 43 degrees Celsius; kerosene about 38 to 72 degrees Celsius.
- Petrol flash point
- Approximately negative 43 degrees Celsius
- Kerosene flash point range
- 38 to 72 degrees Celsius
- Key distinction
- Requires a pilot flame to ignite, unlike auto-ignition temperature
Common questions
What's the difference between flash point and auto-ignition temperature?+
Flash point is the lowest temperature at which a liquid produces enough vapor to form an ignitable mixture when a pilot flame is present. Auto-ignition temperature is higher - it's when the liquid ignites on its own without any external flame. Fire investigators distinguish between them because they affect how accelerants behave in fires.
Why does flash point matter in fire investigations?+
Flash point is critical for identifying and classifying accelerants used in arson cases. Different liquids have distinct flash points - petrol around negative 43 degrees Celsius, kerosene between 38 and 72 degrees Celsius. These characteristic temperatures help investigators determine what substances were present and how they contributed to a fire's spread.
Does a liquid burn at its flash point?+
No. At the flash point, the liquid produces enough vapor to ignite in the presence of a flame, but the vapor does not sustain combustion on its own. You need that external heat source. The vapors will ignite and then extinguish if the heat source is removed.
Related terms
- Fire Tetrahedron
- The model of sustained combustion requiring four concurrent elements: fuel, oxidiser, heat, and an uninhibited radical chain reaction. Replacing the older fire...
- 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...
- 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...
- Backdraft
- A deflagration event triggered when air is suddenly admitted to a compartment where a fire has been oxygen-depleted but has continued to...
- 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...
- 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...
- Fire Point
- Slightly above flash point, the temperature at which sustained combustion begins after ignition.
- Fire Triangle
- The three components needed for combustion: fuel, heat and oxygen. Remove any one and the fire stops.
- Flaming Combustion
- Gas-phase oxidation of volatile pyrolysis products above the fuel surface, producing a visible flame at 800-1200°C. Produces less CO than smouldering under...
- 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...
- Glowing (Smouldering) Combustion
- Surface-phase oxidation of solid char without a gas-phase flame, typically at 400-700°C. Produces large amounts of CO and can persist at lower...
Explained in these topics
- Fire and Arson Investigation: Cause, Origin and Burn PatternsLowest temperature at which a liquid gives off enough vapour to form an ignitable mixture in air, but the vapour does not sustain combustion. Petrol about minu...
- Fire Chemistry: Combustion, Oxidation and the Fire TetrahedronThe minimum temperature at which a liquid produces sufficient vapour to ignite in the presence of a pilot flame, distinct from auto-ignition temperature. Criti...