User Manual

Fire Safety
60
Building Technologies 049_Archives_and_Libraries_A6
V10271399_a_en.doc
Fire Safety & Security Products 03.2009
be put efficiently. If the fire is an open flame fire, additionally there is the advantage
that building up the extinguishing concentration in short time will minimize the pro-
duction of the harmful HF (Hydrofluoric Acid)
When designing natural agent systems it is also important to fulfill the specified
discharge times (ISO 60s / VdS 120s), in order to assure fast extinguishing con-
centration build up.
Unclosable Openings and forced ventilation
Openings shall be arranged to close automatically before or simultaneously with
the start of the discharge. Small openings are permissible provided they do not ex-
ceed a certain limit and are compensated for by the addition of extra extinguishant.
Forced air ventilation systems shall, whenever possible, be shut down before or
simultaneously with the start of the discharge. If this cannot be done it may be pos-
sible to compensate for losses. If there is a short run down time but the quantity of
air removed is significant, additional extinguishing agent shall be applied.
Maximum recommended nozzle coverage: 30 m
2
It is important to note that using nozzle area coverage greater than 30 m
2
gener-
ates higher turbulences and noise during discharge. This consideration must be
specially considered when protecting archives and libraries.
Additionally higher nozzle coverage means higher extinguishing agent flows. When
extinguishing with chemical agents, excessively high flows per nozzle provoke that
full evaporation of the agent cannot be achieved, leading to liquid agent drop under
the nozzle. Let’s remember chemical agents extinguish in their gas phase.
Let’s see an example:
Risk A
Area = 405 m
2
Volume = 2.100 m
3
Novec 1230: 1750 Kg Novec
Using 30 m
2
nozzle coverage:
– Number of nozzles: 14
– Kg of Novec per nozzle per second: 4 Kg/s per nozzle  recommended
Using 80 m
2
nozzle coverage:
– Number of nozzles: 5
– Kg of Novec per nozzle per second: 12 Kg/s per nozzle  NOT RECOM-
MENDED!!!
Discharging 12 Kg of fluid per nozzle per second would certainly not assure homo-
geneous distribution and total evaporation (most probably a stream of liquid agent
would be observed dropping under the nozzle) and chemical extinguishing agents
extinguish in their gas phase! Additionally the extinguishing concentration will not
be reached in 10 seconds, or probably never reached, since the liquid poured on
the floor will not build up extinguishing concentration.
Of course the system in the second example is more economic, but the one in the
first example is the one that will certainly extinguish the fire.