User Manual

Siemens Switzerland Ltd 28
Building Technologies Division
4.4.3. Wall hydrants
Wall hydrants are used to complement fire extinguishers in dealing with incipient stage fires. They are intended
both for trained staff and fire service use. Wall hydrants are evenly distributed throughout the building, providing
water outlets from the building’s extinguishing water pipe network. Care must be taken to prevent contamination
of the drinking water supply by the water used for extinguishing. For this reason the extinguishing water is
generally taken from a separate water supply tank and fed under pressure into the pipe network via fire pumps.
4.4.4. Sprinkler systems
The primary purpose of a fire sprinkler (or pre-action) system is to douse or confine the fire through the
application of water to its area or room of origin in order to protect the structure. Actually taking NFPA 75 into
account, sprinklers are intended to protect the building, hence it recommends sprinklers. However, in case of a
fire sprinklers are damaging the electronic equipment in data center and eventually causing short circuits that
would further ignite fires across the area.
Water sprinklers are usually present in the server room because server rooms are usually developed using existing
office space already fitted with water sprinklers. It essentially consists of a grid of water pipes equipped with
fusible heads that melt over a certain temperature to allow pressurized water to spray over a specific area.
In using sprinkler systems important limitations have to be borne in mind:
• Limited to Class A fire suppression
• Likelihood of accidental discharge if a head or pipe is broken
• Requires significant cleanup time regardless of the event that triggered the discharge
• Will cause significant collateral water damage to IT equipment and surroundings
Pre-action water systems, similar as a water sprinkler system except they require at least two alarm conditions to
be activated, can also be used as an alternative.
In this case an accidental activation will not cause the system to discharge because an event triggering an alarm
must be followed by a second event confirming a fire condition (e.g. a broken sprinkler head alone would not
cause system discharge unless smoke or heat is also detected) before system discharge takes place. This
confirmation mechanism explains the term "pre-action." Generally conventional water sprinkler systems can be
converted to pre-action systems with small money. Analogously to water sprinkler systems, pre-action implies
major drawbacks in computer room applications:
• Limited to Class A fire suppression
• More costly than a conventional water sprinkler system
• Requires significant cleanup time regardless of the event that triggered the discharge
• Can be zoned, but discharge sometimes takes place throughout the entire zone
• Will cause significant water damage to IT equipment and surrounding finishes or materials
In either case false floor and strong air-ventilation determine additional drawbacks for using sprinklers in
computer rooms due to lack of protection in the first case and spread of fire in the second respectively.
In general, sprinkler systems protect the building while dry extinguishing systems protect data and the
equipment. In some cases dry extinguishing systems cannot take the place of a sprinkler system, it can only be
installed in addition to it. At the end of the day, the local fire inspection is the authority and has jurisdiction over
what is permissible.
For the protection of the assets Siemens therefore recommends to use dry extinguishing systems to keep the
electronic equipment safe. If a fire does occur, the first step is rapid detection. There are a number of advanced
detectors that sense fire in its early stages and then trigger an automated dry extinguishing system before a
sprinkler system is being activated.