Theory 08/Fire Safety Engineering
Facade Fire Is a Cavity Ratio
The claim
Vertical fire spread in a ventilated facade is set by the ratio of cavity width to flame height, so a narrow cavity can propagate faster than a wide one.
01Mechanism
A narrow cavity channels the plume and increases convective heating of the inner leaf; beyond a width, the plume loses contact with both surfaces.
02Predictions
- P1Spread should peak at an intermediate cavity width.
- P2Wider cavities should not always be worse.
03Refutation
Spread increasing monotonically with cavity width would remove the optimum.