| Automatic
Fire Protection |
The computer room
may be protected from a fire by the installation
of an automatic extinguishing system.
Alternatives
The mediums used to extinguish may be water,
foam or gas. Water and foam have problems regarding
residues that may be left on circuit boards
as well as their removal from the room afterwards.
Sprinklers are usually present only to protect
the structure of the premises rather than its
contents. When installed in computer rooms they
need to be dry systems. This means that they
do not carry a charge of water until fire has
been detected. Then the system relies on heat
sensitive bulbs in the sprinkler points to spray
water onto heat sources below.
Gas
The most commonly used system is gas.
Only non-toxic, inert and environmentally-friendly
gases are permitted. We recommend Inergen and
Argonite. FP200 is another.
All consist of naturally occurring inert gases.
They work by displacement of the normal percentage
of oxygen held within air, reducing it to a
level at which combustion is inhibited.
To assist any human caught in a discharge, carbon
dioxide is added.
This causes more rapid breathing – which
compensates for the reduced oxygen available.
As the gases are inert, no toxic byproducts
are produced and therefore the fire brigade
may not require special fume removal means.
The gases are stored in their gaseous state
at room temperature. When released into the
space they are protecting, there is no fogging
of the air due to water vapour condensation.
Operation
Release of the extinguishing medium –
apart from water sprinkling, described previously,
is arranged via the smoke detection system.
To reduce the chance of a false alarm, we arrange
the smoke detectors into separate zones and
hold release of the flood system until detectors
on two separate zones have activated. This is
known as “double-knock”.
As a further safeguard against false alarms,
a delay between the extinguishing system receiving
its double knock alarm and its activation is
provided. During this period, personnel have
the opportunity to leave the protected area,
or to turn off the system and attend to the
fire condition by other means.
A manual release is available outside the entrance
to the room. This overrides the control system
and leaves a decision to activate the extinguishing
in human hands.
Installation
This requires containers, bottles in the case
of gas, stored either inside or outside the
room, connected to a manifold which distributes
to pipework laid in the raised floor and suspended
ceiling voids, to distribution nozzles covering
the areas to be protected.
Areas covered
There is a point of view calling into question
the necessity to protect all the voids in the
computer room.
It considers that the most likely source of
fire is in the concealed void, beneath the raised
floor, where the vast majority of electrical
connections are located.
Another suggests that the ceiling void does
not need protection as it has the least electrical
connections.
We feel that the whole space should be protected.
Leaving the ceiling void out would lead to the
question of how containment of the gas in the
remaining areas could be achieved. If the ceiling
void was so voluminous as to have large financial
implications, it should be reduced by the insertion
of a secondary plenum ceiling. |
