- An Emergency Voice Alarm Communication system is part of a fire alarm system that uses high reliability speakers to notify the occupants of the need for action case of fire or other emergency.
- These speakers are special types of fire alarm Notification Appliances.
- Emergency Voice Alarm Communication systems are employed in large facilities where general undirected evacuation is considered impracticable or undesirable.
- The Audible Textual signals from the speakers are used to direct the occupant’s response during a fire or other emergency.
- The system may be controlled from one or more locations within the building known as Fire Wardens Stations, or from a single location designated as the building Fire Command Centre.
- Speakers are automatically activated by the fire services alarm system in a fire event and following a pre-alert tone, selected groups of speakers may transmit one or more pre-recorded messages directing the occupants to safety.
- These messages may be repeated in one or more languages.
- Trained personnel activating and speaking into a dedicated microphone can suppress the replay of automated messages in order to initiate or relay real time voice instructions.
Pre-action sprinkler systems are specialised for use in locations where accidental activation is undesired, such as in museums with rare art works, manuscripts, or books.
Pre-action systems are hybrids of wet, dry and deluge systems, depending on the exact system goal. There are two sub-types of pre-action systems: single interlock, and double interlock. The operation of single interlock systems are similar to dry systems except that these systems require that a and supervised event (typically the activation of a heat or smoke detector) takes place prior to the action of water introduction into the system piping due to opening of the pre-action valve (which is a mechanically latched valve). Once the fire is detected by the fire alarm system, the system is essentially converted from a dry system into a wet system. Or, if an automatic sprinkler operated prior to the fire being detected by the fire alarm system, water will be allowed into the piping and will discharge water from the sprinkler.
The operation of double interlock systems are similar to deluge systems except that automatic sprinklers are used. These systems require that both a preceding and supervised event (typically the activation of a heat or smoke detector) and an automatic sprinkler activation take place prior the the action of water introduction into the system piping. There is also a little used variation known as Non-Interlock.
Dry pipe systems can only be used (by regulation) in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, rendering the system inoperable. Dry pipe systems are most often used in unheated buildings, in outside canopies attached to heated buildings (in which a wet pipe system would be provided), or in refrigerated coolers. Dry pipe systems are the second most common sprinkler system type.
Water is not present in the piping until the system operates. The piping is pressurized with air, at a “maintenance” pressure which is relatively low compared with the water supply pressure. To prevent the larger water supply pressure from forcing water into the piping, the design of the dry pipe valve (a specialized type of check valve) intentionally includes a larger valve clapper area exposed to the maintenance air pressure, as compared to the water pressure.
Operation – When one or more of the automatic sprinklers is exposed to sufficient heat, it operates, allowing the maintenance air to vent from that sprinkler. Each sprinkler operates individually as the air pressure in the piping drops, the pressure differential across the dry pipe valve changes, allowing water to enter the piping system. Water flow from sprinklers needed to control the fire is delayed until the air is vented from the sprinklers. For this reason, dry pipe systems will only provide a slight delay prior to water discharge while the air in the piping is released prior to the water filling the pipe.
“Deluge” systems are systems that have open sprinklers, i.e. the heat sensing operating element is removed during installation, so that all sprinklers connected to the water piping system are open. These systems are used for special hazards where rapid fire spread is a concern, as they provide a simultaneous application of water over the entire hazard.
Water is not present in the piping until the system operates. Because the sprinkler offices are open, the piping is at ambient air pressure. To prevent the water supply pressure from forcing water into the piping, a deluge valve is used in the water supply connection, which is a mechanically latched valve. It is a non-resetting valve, and stays open once tripped.
A foam water sprinkler system is a special application system, discharging a mixture of water and low expansion foam concentrate, resulting in a foam spray from the sprinkler. These systems are usually used with special hazards occupancies associated with high challenge fires, such as flammable liquids and airport hangars. Operation is as described above, depending on the system type into which the foam is injected.