THE STAGES OF THE TESTING
The DFT is conceptually develops in 3 stages:
MEASURE: It measures the injected / extracted air flow entities in / from the local to generate inside a given value for the overpressure / depression.
CALCULATION: From the measured values we can calculate the equivalent leakage area (ELA: Equivalent Leakage Area), ie the total area of all leaks, cracks, joints and porous surfaces that allow leakage from the local subdivision surfaces in question.
PREDICTION: Knowing the value of Equivalent Leakage Area you can perform a valuation of the gas retention time in the room.
THE TEST PROCEDURE
Let’s now look at the Door Fan Test procedure in detail to understand what principles it is based on.
Measurement and Calculation
The procedure followed in the execution of a Test involves entering a stream of air into the room to Pressurize it to the overpressure value that would be determined by a real discharge of extinguishing agent inside it. The measurement of the input air flow gives an indication of the leakage (ie of the flow of air coming out). Indeed, under equilibrium conditions, it results in the unit of time: incoming air volume = outgoing air volume.
Knowing, therefore, the air flow rate, the fan discharge coefficient in the presence of a laminar air flow, induced overpressure and air density can accurately calculate the ELA as the theoretical area of a hole from the outlines, through which passes all the leakage flow, to the test pressure. The same type of test will be repeated by performing a Depressurization of the room in order to minimize the influence on Static Pressure measurement, ie a pressure delta between the interior and exterior of the room already present before the test begins. of ELA will be given by the mean between the two values obtained as described above
SEALING OF LOSSES
Full repetition of the test
In carrying out the tests described, the leak is searched through the use of chemical smoke.
The use of the smoke generates a modest introduction into the environment during the pressurization phase
amount of smoke, by means of special “smoke puffers” (a sort of smoke emitter), in close proximity
cracks and probable leaks, to appreciate smoking outbreaks, which allows you to detect
even hidden losses (small cracks in the walls, leaks along the window frames or along the windows
couplings between perimeter panels, etc …).
DOOR FAN TEST Execution
The execution of the DFT before the project predisposition, therefore allows verification of the feasibility of a gas-saturation protection system within the volume to be protected, while also allowing to assess the technical and economic convenience of alternative solutions. It also provides at the design information necessary for the determination of any factors Project or maintenance discharges, also in relation to the dangers associated with the presence of people in the protected rooms. In the following, we will describe what are the aspects that most affect the protected volume of sealing characteristics, making from time to time refer to local real cases object of Door Fan Test.