ADA recommends that a composite flash rate in excess of 5 Hz shall be avoided for multiple strobes installed in the field of view, and indicates that the use of synchronized strobes should provide an acceptable alternative when more than two strobes are installed in the same field of view. In addition, it is important to remember that in order to meet ADA’s concern for effectively alerting the hearing impaired, strobe flash rates must be a minimum of one flash per second, across the Regulated* voltage range. Using lower intensity synchronized strobes can provide better alerting since occupants can often directly view the strobe flash. In addition, the selection of strobe intensity and location is simplified.
Synchronized Temporal Pattern
NFPA 72 (Chapter 6, Sections 6.8.6.4) requires the use of the temporal pattern (Code 3) audible signal for public mode evacuation. To insure that the sounds from multiple signals within a specified area do not overlap and interfere with the distinctive temporal pattern, the devices shall be synchronized. Since a majority of fire alarm installations are retrofit applications, the ability to install synchronized appliances using two wires becomes a significant issue. With the use of two (2) wire signaling appliances, such as The Wheelock Series AS and NS, existing wiring may not have to be replaced unless the current capacity of the existing NAC circuit needs to be increased.
Evacuation Signal Zoning
NFPA 72 (Chapter 6, Section 6.8.6.4.3) requires synchronization of notification appliance circuits within an evacuation signaling zone.
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