User Manual

Siemens Switzerland Ltd 33
Building Technologies Division
The extinguishing agent concentration in the area to be protected is one of the
key parameters (design concentration). The entire gas extinguishing system
design must aim at establishing the desired concentration within the so-called
flooding time, in the room to be protected. Of course, it is vital that the room to
be protected is capable of allowing the establishment of the extinguishing agent
concentration and maintaining it during the retention time. Decisive here is that
the number of unavoidable existing leakage must not exceed a certain threshold,
that would avoid reaching the retention time (10 min. according to VdS, or what
local authorities mandate) or turns the system uneconomic due to the need of
extended discharge to supplement the leakage.
Two methods have proven themselves as control instruments:
1 Actual discharge test with concentration measurement devices
2 Door fan test (see below paragraph “Room integrity, retention time and
door fan test”)
As a rule, the door fan test is preferred over the real discharge test for technical
and/or economic reasons. This test provides an estimate of the leakage area on
the outside limiting shell of the protected area. Limiting shells are construction
elements that protect the room against the outside and ensure gas tightness.
Non-gas tight structures, partitions, raised floors and ceiling voids are not
considered limiting shells. The above mentioned structures are viewed as non-
existent if conducting the door fan method. The risk of insufficient extinguishing
gas concentration may arise if these elements are not considered when
calculating the amount of extinguishing gas required.
Siemens recommends these areas to be considered when calculating the design
volume and to even install extinguishing nozzles in these areas. Siemens also
recommends that ceiling panels are properly closed and secured. Under no
circumstances should the discharging extinguishing agent displace individual
ceiling panels, which would allow the gas into the ceiling volume. In this event,
the risk arises that the system can no longer establish the required concentration
of extinguishing agent and therefore reducing the very success of the
extinguishing system.
Room integrity, hold time
and door fan test
It is essential to determine the likely period during which the extinguishing
concentration will be maintained within the protected enclosure. This is known
as the holding time. The predicted holding time shall be determined by the door
fan test.
Holding time
Room integrity of the protected area is a key issue. A leaky room or enclosure will
not retain the extinguishing agent for long enough, so the fire could reignite.
Failure to achieve the retention time is not a failing of the extinguishing system;
it’s a failure of the customer’s room or enclosure. Very few rooms are entirely
airtight. Especially in data centers where cabling, ventilation, lighting and other
systems are connected to the protected volume, small gaps are likely to occur:
• around doors and windows
• where stud walls join the floor and ceiling
• at cable entries
• through the floor and ceiling tiles
• into light fittings
• into power points
• through plasterboard
Obvious visible leaks (e.g. at cable entries) can be sealed, others may be
impossible to locate or seal.