Are wireless fire alarms right for your project?

03/20/2013


Listing

Figure 3: Various codes and standards books, including different editions of NFPA 72, regulate wireless fire alarm systems. Courtesy: Lynn NielsonWireless fire alarm systems are required to be specifically listed. UL Standard 864, Standard for Control Units and Accessories for Fire Alarm Systems, is used for wired and wireless radio fire alarm systems. The UL standard has a section that specifically addresses low-power RF signaling common performance and monitoring for integrity of protected premises units/systems. Likewise, FM Global Standard 3010, Approval Standard for Fire Alarm Signaling Systems, is used by FM for approval of low-powered wireless systems. A few manufacturers have received UL or FM approvals for their systems. It should also be noted that manufacturers of these systems also must comply with the low-power requirements of Title 47, Code of Federal Regulations, Part 15.

Power supply

Batteries are permitted to serve as the sole power supply of wireless systems. Manufacturers of these wireless fire alarm transmitter devices that use batteries as the sole power supply are required to design the system so each transmitter serves one device that is uniquely identifiable, size the battery with sufficient capacity to operate normally for at least 1 year, transmit a distinctive battery depletion signal before the battery has reached the level required to transmit an alarm signal, generate a trouble signal at the fire alarm control unit when a battery catastrophically fails, and have no impact on other transmitters when a transmitter battery fails.

A change for NFPA 72-2013 includes requiring an audible trouble signal associated with signaling the depletion or failure of the primary battery of a wireless system to automatically resound at the protected premises every 4 hours or less until the depletion signal is restored to normal.

Alarm signals

When an alarm-initiating device is actuated, code requires an automatic transmission to be sent. The signal processing between the time the initiating device is actuated and the control panel displays the alarm cannot exceed 10 seconds. Transmitters are required to repeat the alarm transmission every minute or less until the initiating device is restored. This section requires the manufacturers’ control equipment to latch alarm signals until manually reset and also establishes signal priorities for manufacturers.

Changes for NFPA 72-2013 include changes to alarm signals that impacts wireless radio fire alarm systems. Specifically, clarification was added in the form of a modifier on the type of alarm signals required to latch. Only fire alarm signals will be required to latch until manually reset. Additional language was placed into the annex to clarify which signals are required to latch.

Monitoring for integrity

Manufacturers are required to use transmission methods that are resistant to misinterpretation of simultaneous transmission and to interference. This is examined as part of the product listing. To ensure the integrity and capability of the signal pathway, the control equipment is required to poll the transmitters every 200 seconds or less (note that some special exceptions, which will expire on June 30, 2013, extend the polling period). If a transmitter fails the pathway, verification of a fault is generated. If a fault is generated, it cannot cause an alarm signal. If a transmitter is removed, a supervisory signal is generated on the control equipment. If signal interference is detected for 20 or more consecutive seconds, then an audible/visual trouble signal is annunciated on the control equipment.

Output signals for receiver/control

Low-powered radio fire control equipment that initiates fire control functions or notification appliances wirelessly is required to comply with specific requirements that regulate power supplies, monitoring for integrity, response time, signal repeating, and output latching until manually reset.

Acceptance testing and reacceptance testing

In addition to the standard acceptance testing criteria, wireless systems also require the following to verify wireless protection system operation:

  • The manufacturer’s designated representative performs an initial testing phase and verifies correct operation.
  • The existence of alternative communications paths is confirmed between the wireless control unit and peripheral devices used to establish alarm and trouble initiation, indication, control, and annunciation.
  • Batteries are checked in the system monthly unless the control unit checks all batteries and all components daily. 

Smoke alarms and wireless technology

Figure 4: CWSI offers several examples of wireless fire alarm products, including detectors and alarms. Courtesy: Commercial Wireless Systems International (CWSI)A smoke alarm is not the same thing as a smoke detector. A smoke detector requires a connection to a control panel to provide notification. A smoke alarm (also known as a single or multiple station alarm) responds to smoke as a stimulus and produces alarm notification without external control equipment. Each device includes a smoke chamber, alarm sounder, power supply, and associated electronics allowing it to sense smoke and initiate an audible alarm. Some also provide visible alarm notification.

The primary technological differences between a smoke alarm and a smoke detector are how the devices are interconnected and the power source. Interconnection of smoke alarms is required for all new installations where more than one smoke alarm is required within a sleeping unit, suite, dwelling, or house. Interconnected devices activate the audible or audible/visual notification feature in each device in unison, resulting in a simultaneous alarm.

Hardwired smoke alarms are interconnected through wiring with other smoke alarms. Wireless smoke alarms also can be interconnected to other wireless smoke alarms through RF signaling pathways. This interconnect enables them to produce a simultaneous audible alarm signal upon activation of any smoke alarm. As with most wired interconnected smoke alarms, most wireless interconnected smoke alarms are not required to be supervised. As shown in the floor plan, the primary benefit of using interconnected wireless smoke alarms is the interconnection itself. A secondary benefit is the elimination of the wiring between devices. Hardwired and wireless smoke alarms can provide earlier warning to escape because of the common alarm notification that interconnection provides throughout the unit.


Lynn Nielson is a registered professional fire protection engineer and a past president of the Society of Fire Protection Engineers’ (SFPE) Southern Nevada Chapter. He is a member of NFPA, the Technical Correlating Committee for Fire Alarm Systems, and the Technical Committee for Initiating Devices. Jim Avanzino retired from Siemens Industry Inc., where he was a regional manager. He is a member of SFPE’s Southern Nevada Chapter.


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