Supervisory Signals for a Fire Sprinkler System
A fire alarm system is being installed in a warehouse that is protected by a wet-pipe sprinkler system. The sprinkler system has a main control valve, a pressure switch, and a waterflow switch. The fire alarm control unit (FACU) is programmed to monitor the waterflow switch for alarm and the main control valve for supervisory. The pressure switch is not connected to the FACU. The contractor has installed the system and is ready for acceptance testing. The owner wants to know if the system meets NFPA 72 requirements for supervisory signals. The warehouse has a dry-pipe sprinkler system in an unheated storage area. The dry-pipe valve has a low-pressure switch that is not monitored. The plan reviewer must evaluate the supervisory signal requirements.
1. What supervisory signals are required by NFPA 72 for this sprinkler system?
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NFPA 72 requires that the fire alarm system monitor supervisory signals for certain conditions. For a wet-pipe sprinkler system, the main control valve must be monitored to indicate a closed or off-normal position. The pressure switch may be used to monitor for low air pressure in a dry-pipe system, but in a wet-pipe system, it may not be required. However, the dry-pipe system in the unheated storage area requires monitoring of the air pressure to ensure the dry-pipe valve is operational. NFPA 72 requires that a low-air-pressure supervisory signal be provided for dry-pipe systems. The pressure switch on the wet system may be for other purposes, such as monitoring for excessive pressure, but it is not typically a required supervisory signal. The contractor has not connected the pressure switch, which may be acceptable if it is not required. However, the dry-pipe low-pressure switch must be monitored as a supervisory signal. The FACU should be programmed to indicate a supervisory condition when the low-pressure switch activates. Additionally, the main control valve for the dry-pipe system must also be monitored. The plan reviewer should require that all supervisory signals be connected and tested.
2. How should the FACU be programmed to handle supervisory signals, and what are the notification requirements?
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The FACU must be programmed to annunciate supervisory signals distinctly from alarm signals. NFPA 72 requires that supervisory signals be indicated by a visual and audible signal that is distinct from alarm signals. The supervisory signal must be transmitted to a central station if the system is monitored. The FACU should have a supervisory indicator and a supervisory sound that is different from the alarm sound. The supervisory signal should latch until acknowledged. The notification appliances for supervisory signals are not required to be the same as alarm notification appliances; often, a separate supervisory sounder is used. The plan reviewer should verify that the sequence of operations includes supervisory signal handling and that the FACU is listed for the intended use. The contractor should test the supervisory signals by operating the valve and the low-pressure switch to ensure proper annunciation and transmission.