Fire alarm sounders

At least one fire alarm sounder will be required in each zone, but all sounders in the building must operate when the alarm is activated. 

Total simultaneous evacuation - the most common way to achieve simultaneous evacuation is that upon the activation of a single call point or detector an instantaneous warning from all fire alarm sounders is given as the signal for an immediate evacuation. This is referred to as a single stage evacuation. 

In a two-staged evacuation, there is an investigation period before the fire alarm sounders are activated. This approach is adopted for facilities such as halls of residence (student accommodation) and places of public entertainment. A staged evacuation ensures that confirmation of a fire can be verified prior to running the risk of... 

In a large proportion of buildings a simple evacuation strategy will be adopted and on the operation of a manual call point or detection by an automatic fire detector, fire alarm sounders will provide warning and indicate the need for a full evacuation of the building. 

Zones - to support the above arrangements the building will need to be divided into a number of alarm zones in such a way that the fire alarm sounders reflect an operation of a manual call point within that area or a detector. 

Fire alarm circuits are wired as either normally open or normally closed. In a normally open circuit the alarm call points are connected in parallel with each other so that when any alarm point is initiated the circuit is completed and the sounder gives a warning of fire. In a normally closed circuit the alarm call points are connected in series to normally closed contacts. When the alarm is initiated, or if a break occurs in the wiring, the alarm is activated. 

In a normally open oirouit, the alarm call points are connected in parallel with each other so that when any alarm point is initiated the circuit is completed and the sounder gives a warning of fire. 

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