Normally closed fire alarm

The presence of a trench/pipe system in Option B, used to remove rain accumulations, increases the risk that contaminated fire water might be inadvertently discharged into the sanitary sewer system. In order to reduce this risk, it is necessary to install a motorized valve in the drainage piping. This valve could be arranged to close automatically in the event of a fire through a signal from the fire alarm panel and manually as needed. It may also be desirable to use a valve which will automatically close in the event of loss of power. Alternatively, this valve could be normally closed and opened when needed. 

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. 

Fire alarm circuits are wired as either normaiiy open or normally closed. 

When a fire occurs, the heat produced will fuse a sprinkler, causing water to flow. The waterflow indicator is activated by the water flow. The paddle, which normally lies motionless inside the pipe, is forced up, thereby activating the pneumatic time delay mechanism, which closes or opens a microswitch after the preset retard time has elapsed. This action causes an electric alarm to sound. The alarm will continue to sound as long as there is a flow of water in the system. The water will flow until it is shut off manually. 

Self-closing All fire doors should be fitted with self-closing devices that are maintained so that the door closes positively against the door stops and where appropriate latches effectively. The notable exceptions to this are those doors that are normally kept locked shut, e.g. doors to cupboards or service ducts.Where it is considered a hindrance to have a fire door closed at all times it may be held open by an automatic release mechanism that is actuated by an automatic detection and alarm system. 

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