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Ventilation Factor and Compartment Fire
The ventilation factor F = A_v·√H_v and the heat release rate the opening can sustain, deriving the familiar coefficient from its two components.
Fire stage
The correlation describes a fully developed, post-flashover fire. There is no default, because this is the question that decides whether the result means anything at all.
Ventilation type
The ventilation openings
For comparison — optional
This can be taken from the pool fire calculator. If entered, the tool compares the two and states which of them governs. Without it, no such finding is shown.
Where 1,500 comes from
The familiar form is Q̇ ≈ 1500·A_v·√H_v, but 1,500 is not a constant of nature — it is the product of two separate approximations:
- •0.5 kg/s per m^2.5 — the air a vertical opening admits under buoyancy when the fire is drawing all it can.
- •3,000 kJ per kg of air — the heat released per kilogram of air consumed. This is the term that makes the correlation possible: heat per kg of fuel varies by an order of magnitude between materials, but per kg of air it is close to 3,000 for most ordinary combustibles, because it is the oxygen that limits it rather than the identity of the fuel.
Both terms appear separately in the calculation breakdown, and the coefficient appears at the end of it as a consequence.
The equation
Q̇_vent = 0.5 · A_v · √H_v · 3000
- Q̇_vent [kW]
- Ventilation-controlled heat release rate
- A_v [m²]
- Area of the opening
- H_v [m]
- Height of the opening
Values required for the calculation that do not vary within the equation:
- The fire stage is not a variable in the equation. It decides whether the equation applies at all — a fire in its growth stage does not get a different number, it gets no number.
- The ventilation type is not a variable in the equation. Under mechanical ventilation the fan sets the air supply rather than the opening, and the 0.5 factor does not exist.
Ventilation-controlled compartment fire — SFPE Handbook 5th ed.
Result
Missing dataA value is missing that you can supply here and now.
No result was calculated. The details are below.
To complete the calculation the following are missing:
- Ventilation type
- Fire stage
Validity range
A single compartment with a vertical opening, a fully developed post-flashover fire, natural ventilation. Mechanical ventilation and a fire in its growth stage get no number — they are not a less accurate case but a case the correlation does not describe.
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