Fire alarm systems:

All buildings require a means by which the warning  of  fire  can  be  given  to  all occupants.  In the very smallest premises this might be achievable by shouting 'Fire!' but in all other buildings there will be a need for an electronic system to raise the alarm throughout the building.

The systems have to be completely reliable so they usually contain their own back-up battery power supply so that they can work even if there is a power cut. Sounders have to be loud enough to be heard by everyone.  

In very noisy buildings it is sometimes  necessary  to  install flashing  beacons  to  give  the  warning  signal. Sometimes the sounders are deliberately very loud so that they are uncomfortable and drive occupants out of the building.  This is thought, by some, to be necessary because some occupants canbe very reluctant to evacuate and will carry on doing what they were doing before that alarm sounded.                                    

Sounders should not be so loud to cause damage to the ears and some standards specify 120dBA as the maximum sound level allowed.  Sounders should be kept away from the area that is occupied by the person who is expected to call the fire service in the event of an emergency. The fire alarm does not generally have to be very loud in the staircases.

Where there is a possibility that a fire can go un-noticed by the occupants it is often necessary to install automatic fire detection.   The most effective detection is smoke detection but this can be vulnerable to steam, dust, insects and other contaminants and in  areas  where  this  might  cause false  alarms it  will  be  necessary  to  install  heat detectors instead of smoke detectors.