Assessing wireless fire alarm systems
- Explain how NFPA 72: National Fire Alarm and Signaling Code directs engineers in their design of wireless fire alarm systems.
- Review case studies that incorporate low-power wireless fire alarm systems.
Often considered new technology, commercial wireless fire alarm systems have now been in existence for more than 30 years. Prior to 1987, the use of wireless fire alarm systems suffered due to the lack of listing standard criteria, absence of recognition in what is now referred to as NFPA 72: National Fire Alarm and Signaling Code, and overall concerns with performance features.
With the development of UL standards for wireless fire alarm systems and requirements being included in NFPA 72 in 1987, commercial fire alarm systems as we know them today were born and started to become an acceptable technology. Before applications are discussed, let’s first explore the requirements currently in NFPA 72.
The application of the section originally intended to apply to wireless fire alarm systems has been expanded by referring to low-power radio systems. As with more traditional fire alarm system equipment and components, the standard states that equipment in low-power radio systems shall also be listed for use as a fire alarm system (NFPA 72-2016: 23.16.1). While traditional fire alarm systems are required to have a primary and secondary source of power, the primary battery is permitted to be the sole source of power for a low-power radio system (NFPA 72-2016: 23.16.2). However, the reliability of the battery power source is enhanced by requirements that:
- The battery must be capable of operating the transmitter/transceiver for a period of at least 1 year.
- A distinctive, low-battery trouble signal shall sound at least every 4 hours, if the signal is silenced, for a period of at least 7 days prior to the battery not being able to operate the device properly. The trouble signal shall identify the specific transmitter/transceiver served by that battery and each transmitter/transceiver shall serve no more than one device.
- Catastrophic battery failure shall result in a trouble signal, which again will sound every 4 hours if silenced.
- Battery failure in one transmitter/transceiver shall not impact any other transmitter/transceiver.
Alarm signals from low-power radio systems shall have the same priority and response time as required for traditional fire alarm systems. In addition, each transmitter/transceiver shall repeatedly transmit alarm signals every 60 seconds until the initiating device is restored to a non-alarm status.
The integrity of such systems is monitored by requiring trouble signals under the following conditions (NFPA 72-2016: 23.16.4):
- Within 200 seconds of loss of communication with a device
- Immediately upon removal of a transmitter/transceiver from its installed position
- Reception of an interfering transmission.
Lastly, when a low-power radio transmitter/transceiver is used to actuate remote devices, the performance is required to be essentially the same as a traditional fire alarm system.
NFPA 72 contains some additional requirements for the acceptance testing of low-power radio systems, above and beyond the requirements for all fire alarm systems. These include the use of the manufacturer’s published instructions and the as-built drawings provided by the system supplier to verify correct operation after the initial testing phase has been performed by the supplier or by the supplier’s designated representative.
In addition, starting from the functional operating condition, the system shall be initialized in accordance with the manufacturer’s published instructions. The alternative communications path shall be confirmed between the wireless control unit and peripheral devices used to establish initiation, indication, control, and annunciation. Lastly, the system shall be tested for both alarm and trouble conditions (NFPA 72-2016; Table 188.8.131.52).
The First Draft Report for the 2019 edition of NFPA 72 indicates that most of the above provisions will remain unchanged. There is a new section proposed to address situations in which two or more batteries are used to power a device (FR 3009).
NFPA 72 does not limit the applications of low-power radio systems. As such, the choice to use low-power radio systems rests with the designer of the fire alarm system. Common applications are those in which installing fire alarm cable is either costly or challenging. In a historical building, for example, a low-power radio system may be desirable because installing cable in concealed spaces may adversely impact the historical features of the building; installing surface-mounted raceway also is not desirable.
Another benefit of low-power radio systems is the reduced installation time, especially in a retrofit project. Manufacturers of such systems will often cite hotel retrofit projects in which one can install the detection devices faster than the room can be serviced. Today, technology exists that allows for “tandem” smoke operation in residential properties that have multiple smoke alarms/detectors in a common apartment or large hotel room. The installation of a low-power radio system in such facilities should take considerably less time than a traditional fire alarm system with reduced disruption to the residents or guests in the facility.
New and existing buildings
Low-power radio systems, or wireless fire alarm systems, have been available in the United States for more than 3 decades. The reliability and performance of such systems have improved due to the changes in the listing standards and the requirements in NFPA 72.
As with any fire alarm system, when properly designed, installed, inspected, tested, and maintained, low-power radio systems provide the level of system performance required and expected in those situations in which a code requires a building, or portion thereof, to be protected with a fire alarm system.
William E. Koffel is president of Koffel Associates. He is chair of the NFPA Correlating Committee on Life Safety and a member of numerous NFPA technical committees. He is a member of the Consulting-Specifying Engineer editorial advisory board.