![]() ![]() CO (carbon monoxide) detectors are specified to use a similar pattern using four pulses of tone (often referred to as T4). This pattern, which is also used for smoke alarms, is named the Temporal-Three alarm signal, often referred to as "T-3" or "Code-3" (ISO 8201 and ANSI/ASA S3.41 Temporal Pattern) and produces an interrupted four count (three half second pulses, followed by a one and one half second pause, repeated for a minimum of 180 seconds). The pattern is uniform without regard to the sound used. In 1996, the ANSI and the NFPA recommended a standard evacuation pattern to eliminate confusion. Today these methods are confined to applications intended to trigger a response other than evacuation alone. ![]() These are named with respect to their distinctive structure and include, March Time (usually 120 pulses per minute but sometimes at 90 pulses or 20 pulses per minute, depending on the panel), Hi-Lo (two different tones that alternate), Slow-Whoop (slow rising sweep upwards in tone) among others. While less common than a steady sound, differing signaling methods were used for the same purpose. In general, no common standard at that time mandated any particular tone, or pattern for audible fire alarm evacuation signals. The majority of audible notification appliances installed prior to 1996 produced a steady sound for evacuation. 45 dB to 120 dB A weighted for human hearing (higher decibels, in the 100 to 120 dB range, were common with older electromechanical horns) Ĭoding refers to the pattern or tones a notification appliance sounds in and is controlled either by the panel or by setting jumpers or DIP switches on the notification appliances.Used in many current notification devices. Several methods are used and documented in industry specifications published by UL. The primary function of the notification appliance is to alert persons at risk. 6.2 NFPA code implementation of low frequency (520 Hz) sound.6.1 Effectiveness of low frequency (520 Hz) sound. ![]()
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