Flashover
Definition
The near-simultaneous ignition of all exposed combustible surfaces in a compartment, occurring when the upper gas layer reaches approximately 600°C and radiative heat flux to the floor exceeds the critical ignition threshold. Destroys directional burn-pattern evidence of fire origin.
- Temperature threshold
- Approximately 500-650 degrees Celsius at ceiling level
- Heat flux threshold
- Approximately 20 kW/m² radiant heat flux to floor level
- Pattern evidence
- Most directional burn-pattern indicators are destroyed post-flashover
Common questions
What temperature does flashover happen at?+
Flashover typically occurs when the ceiling gas layer reaches approximately 600 degrees Celsius (with a range of 500-650°C depending on conditions). At this point, the radiative heat flux to the floor also reaches a critical threshold of about 20 kW/m², triggering near-simultaneous ignition of all exposed combustible surfaces.
Why does flashover make fire investigation harder?+
Once flashover occurs, the fire is fully developed and consumes most of the burn-pattern indicators that investigators rely on to determine the fire's origin and direction of spread. This loss of evidence makes it difficult to establish where the fire actually started.
What happens during flashover?+
During flashover, nearly all combustible materials in a compartment ignite almost simultaneously in response to intense radiant heat from the hot gas layer above. This marks the transition from a localized, growing fire to a fully involved compartment fire that engulfs the entire room.
Related terms
- Backdraft
- A deflagration event triggered when air is suddenly admitted to a compartment where a fire has been oxygen-depleted but has continued to...
- Fire Tetrahedron
- The model of sustained combustion requiring four concurrent elements: fuel, oxidiser, heat, and an uninhibited radical chain reaction. Replacing the older fire...
- NFPA 921
- US National Fire Protection Association Guide for Fire and Explosion Investigations. The internationally accepted methodology Indian fire investigators and SFSL fire divisions...
- Fire Dynamics Simulator (FDS)
- Computational fluid dynamics software developed by NIST that models fire-driven fluid flow and heat transfer. Used in landmark investigations including Station Nightclub...
- Heat Release Rate (HRR)
- The rate at which a burning material releases energy, measured in kilowatts (kW) or megawatts (MW). Measured by cone calorimetry for material...
- Negative Corpus
- The discredited practice of concluding incendiary fire cause by eliminating all identifiable accidental causes without positive physical evidence of intentional fire-setting. NFPA...
- 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...
- ACM-PE Cladding
- Aluminium composite material with a polyethylene core (Reynobond PE). The combustible cladding type responsible for external fire spread at Grenfell Tower. Now...
- Arc-Flash Bead Metallurgy
- Forensic metallurgical analysis of conductor wire segments to distinguish between arc-flash ignition (producing globular fusion beads) and mechanical fracture followed by fire...
- 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...
- BS 8414-1
- British Standard for external wall systems: fire performance test for facade assemblies. The large-scale test that ACM-PE cladding, as installed at Grenfell...
- Char Depth
- The depth of carbonisation in timber or wood products, used in post-fire investigation to estimate fire duration and intensity at a point....
Explained in these topics
- Fire and Arson Investigation: Cause, Origin and Burn PatternsTransition stage in a compartment fire, typically around 600 degrees Celsius at ceiling level, when all exposed combustible surfaces ignite almost simultaneous...
- Fire and Burn Pattern InterpretationThe transition from a localised fire to a fully involved compartment fire, typically at room temperatures of about 500 to 600 degrees Celsius. Post-flashover s...
- Fire Chemistry, Pyrolysis and the Arson Investigation FrameworkThe near-simultaneous ignition of all exposed combustible surfaces in a compartment, occurring when the upper gas layer reaches approximately 600°C and radiati...
- Fire Dynamics: Flashover, Backdraft and Ventilation-Controlled BurningThe rapid transition from a growing compartment fire to a fully developed fire, characterised by near-simultaneous ignition of all exposed combustible surfaces...
- Fire Origin Engineering and Heat ReleaseThe transition from a growing compartment fire to full-room involvement, triggered when the upper hot-gas layer reaches approximately 500-600 degrees Celsius a...
- Major Arson Casework: Station Nightclub, Grenfell, Uphaar, Kamala MillsThe near-simultaneous ignition of all combustible materials in a compartment when the ceiling gas layer reaches approximately 600°C and radiative heat flux to...