Security and safety control systems - Intelligent Buildings and Building Automation - page 233

A modern control panel uses one or more microprocessors. This allows the
control panel to send and receive digital information to and from the alarm
stations. Each authorized user can also have his or her own unique code or
present his or her identity to activate or deactivate the system. If the system is
not deactivated within a pre-set time after the system is triggered, the system
will generate alarms. Local noise or visual alarms are usually generated. In
the meantime, alarm signals will be sent to the monitoring centre or delegated
remote security mangers via LAN, telephone, Internet or other means.
11.4 Fire alarm systems
The function of fire alarm systems is to detect the presence of unwanted fire
in the protected spaces by monitoring environmental changes associated with
combustion. Fire alarm systems may be activated automatically, manually or
usually both. The purpose of using fire alarm systems is to notify people to
evacuate in the event of a fire or other emergency, to call the fire protection
department for emergency aid, and to activate other associated systems to
control the spread of fire and smoke. It is worth noting that the fire alarm
system is an essential measure but not the only measure for the fire safety
of a building in terms of both regulations and reality. Concerning fire alarm
systems, it is critical to properly select and place the detectors according to
the layout and use of spaces. This section discusses the basic components and
the typical configurations of fire alarm systems.
11.4.1 Typical fi re detectors
A fire alarm can be initiated manually or automatically. Manually operated
devices, such as a 'break-glass' alarm, provide the means for occupants to
activate the fire alarm system when they observe a fire or smoke. Automatic
fire detectors commonly used can be summarized into the following types,
including: heat detector (or heat-sensing fire detector) , smoke detector (or
smoke-sensing fire detector) and flame detector (or flame-sensing radiant
energy fire detector). Different types of detectors have different detection
speeds and probability of false alarms. Different types may be used to
increase the detection speed and to enhance system reliability.
Heat detectors: A heat detector detects fire by sensing changes in ambient
temperature. Typically, if the ambient temperature rises above a predeter-
mined threshold an alarm signal is triggered. Heat detectors may work on
the basis of rate-of-rise of temperature, fixed temperature or both. Rate-of-
rise heat detectors are activated by the sudden rise in ambient temperature.
A sudden temperature rise above a change-rate threshold, such as 8 K per
minute, will activate the alarm. Fixed-temperature heat detectors are acti-
vated when the ambient temperature reaches a fixed threshold, such as 58°C.
Heat detectors are usually installed in spaces, such as kitchens or utility
areas, laundry rooms or garages, where smoke and fire detectors should not