DESCRIPTION AND APPLICATION

One of the decisive factors for rapid and successful fire suppression in an area protected by a clean agent is its permanence time in the same area. The permanence time of the mixture (soaking) assures the complete suppression of the fire through a cooling effect that avoids the risk of reigniting.

The test protocols for fuels of class A (UL, ISO, CEN) require a minimum permanence time of 10 minutes for the extinguishing agent. During this period the concentration must be kept above the extinguishing value at least up to the level where risky fuels are placed.

In order to calculate this concentration, the standard requires that before the installation of the suppression system, and periodically after its completion, a test called Fan Door Integrity Test be carried on in order to determine the integrity of the volumes to be protected.

Thanks to specific algorithms, the test is able to evaluate the integrity of the volume to be protected and consequently to determine the minimum permanence time for each type of extinguisher.

The test is based on the phenomenon of the descending interface between the air contained in the volume to be protected and the mix air/extinguisher after the latter has been released. In the case of azotes, since the mixes air/extinguishing agent is lighter than air, the interface is moving upwards instead of downwards.

The test in practice measures the pressure differences in the volumes to be protected with calibrated blowing machines, therefore if the blowing stream is known as well as the resulting overpressure, then the equivalent dimension of the existing leaking openings can be predicted.