Ventilation Factor
Definition
A parameter used in fully developed fire characterisation, calculated as Av × Hv^0.5, where Av is the area of ventilation openings (m²) and Hv is their height (m). Used in Thomas's and other correlations to estimate peak fire temperature.
- Formula
- Av × Hv^0.5 (opening area × square root of opening height)
- Units
- Av in m², Hv in m
- Application
- Thomas's correlation and similar peak-temperature estimation models
- Field
- Fire dynamics and compartment fire modelling
Common questions
Why does the formula use the square root of opening height rather than the height itself?+
The square root of the opening height reflects the physics of buoyancy-driven flow through a vertical opening, where the velocity of air being drawn in scales with the square root of the height, so the combined term better represents the actual mass flow of air available to the fire than area or height alone would.
What does a low ventilation factor tell a fire investigator about how the fire likely behaved?+
A low ventilation factor relative to the fuel load present indicates the fire was air-starved for part of its growth, making a ventilation-controlled or even a backdraft-prone regime more likely, which shapes the investigator's expectations for soot patterns and burn severity distribution.
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...
- Deflagration
- A subsonic combustion front propagating through an explosive by thermal conduction. Characteristic of low explosives such as black powder and smokeless powder;...
- Equivalence Ratio (Phi)
- The ratio of actual fuel supply rate to the stoichiometric fuel supply rate for the available air. Values below 1 indicate fuel-controlled...
- 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...
- Fuel-Controlled Fire
- A compartment fire in which the rate of energy release is limited by the fuel supply (surface area, arrangement, reactivity) rather than...
- Hot Gas Layer
- The stratified layer of buoyant combustion gases that accumulates at ceiling level in a compartment fire. Its temperature rise drives flashover when...
- Low Burn Pattern (LBP)
- Fire damage at or near floor level in a compartment. Historically misattributed solely to poured accelerants; now recognised as producible by post-flashover...
- Neutral Plane
- The interface between the hot gas layer above and the cooler ambient air layer below in a compartment fire. Above the neutral...
- Ventilation-Controlled Fire
- A compartment fire in which the rate of energy release is limited by air inflow through ventilation openings. Fuel-rich conditions produce high...