User Manual

Siemens Switzerland Ltd 16
Building Technologies Division
In general, the higher the room, the greater the distance between the seat of fire and the fire detectors on the
ceiling. This is why the intensity of the fire phenomenon to be detected (e.g. smoke density, temperature increase
or radiation intensity) decreases with increasing ceiling height. It must be taken into consideration that with an
increasing ceiling height (and consequent larger room volume) an incipient stage fire can become larger without
necessarily increasing the danger of rapid fire propagation.
High air circulation, for example, significantly dilutes the concentration of smoke. This is why very sensitive smoke
detection systems are often used for this type of application.
2.1.3. Deceptive phenomena
The fire detector has the task of detecting fire from fire aerosols, heat and radiation at an early stage and to
trigger an alarm. Aerosols, heat and radiation, however, are also generated by production processes, by electrical
equipment such as motors, or by environmental factors such as sunlight. If these deceptive phenomena are
sufficiently intense and exist over a certain period of time, they may influence fire detectors enough to trigger an
unwanted alarm.
State-of-the-art fire detectors are largely capable of distinguishing between deceptive phenomena and genuine
fires. However, massive deceptive phenomena are to be expected, predominantly due to strong air-flow up to 15
m/s. A combination of ASD and point-type detectors is highly advisable in order to guarantee early and reliable
detection of fire at pyrolysis stage.
In case of a data center the following needs to be considered in order to avoid false alarms:
• Maintenance work: Due to the generally high air change rate, deceptive phenomena caused by small
works e.g. soldering. During maintenance work the air conditioning may be switched off or reduced
and/or the section should be switched to manual release mode. This allows the system to be discharged
manually should a fire develop during maintenance works.
2.2. Fire detection system
2.2.1. Tasks
The task of an automated fire detection system is to detect fire as early as possible, to sound the alarm and to
activate the preprogrammed control functions.
State-of-the-art fire detection systems are capable of detecting fire very early and as a consequence minimizing
any damage that may be caused. By optimal product selection and appropriate knowledge it is possible to build
systems that virtually rule out unwanted alarms.
The principal requirement on a fire detection system is early and reliable alarming in the event of fire. As a
consequence of this:
• All persons in the danger zone should be able to save themselves.
• Fire control systems can be activated to prevent the fire from spreading to more than one fire sector.
• Response measures can be initiated as early as possible, so that damage to property and operational
interruptions can be reduced to a minimum.