The notification appliance circuit is a vital component of a fire alarm system that warns people about danger. One especially important facet of this system are speakers, chimes, and horns. However, considering the optimal sound level and sound tone of these devices is not an easy task. Depending on the noise level of the occupancy, and the types of occupants, the optimal noise level of your appliances may vary considerably. This problems is especially apparent in sleeping areas, where you have to wake up sleeping occupants.
According to a report by the U.S. Fire Administration (FEMA) bedrooms are the leading location where civilian fire fatalities occur in residential buildings. Furthermore, fatal fires peak between 4 am and 5 am. Thus, warning sleeping occupants is one of the greatest barriers to saving lives during fire emergencies. To this end, it has been shown that low frequency notification appliances are even more effective at waking up sleeping occupants than standard 3150 Hz alarms.
Hertz is commonly used to measure vibrations, particularly sound. Wave frequencies are inversely proportional to their wavelengths, meaning that the longer the wavelength, the lower the frequency. These low frequency sounds can travel longer distances and have high endurance. Most importantly, people are more likely to feel the sound’s vibrations than with higher frequency sounds. These properties of low frequency sounds are one reason why low frequency notification devices are effective at waking people up.
The Fire Protection Research Foundation (FPRF) published a 2007 report called Optimizing Fire Alarm Notification for High-risk groups. In this study, they tested different signals to wake up vulnerable occupants. The signals tested were:
The study indicated that notification devices emitting a low frequency of 520 Hz with a square wave tone are highly effective in alerting vulnerable groups like children, the elderly, individuals with hearing impairments, and those affected by alcohol consumption. Moreover, this sound wave was found to be the most effective for waking up sleeping occupants, waking up 92 percent of hearing-impaired participants when presented at or below 75 dBA for 30 seconds. That means that for hotels, dormitories, assisted living spaces, and for any other occupancies with sleeping rooms, they are best equipped with low frequency notification appliances over conventional standard frequency 3150 Hz devices.
As of January 1st, 2014, it became mandatory for all sleeping areas to be equipped with low frequency alarm signals. The NFPA 72 only requires the use of low frequency 520 Hz alarms under specific circumstances:
Conversely, the NFPA 101 requires all audible alarms initiated by the activation of a smoke detector must be a low frequency 520 Hz alarm regardless of the hearing capabilities of the occupants. The reason for the fire alarm system requirement is that low frequency alarms require more power to operate than standard 3150 Hz alarms. Consequently, it is difficult to create battery-operated low frequency devices due to their power requirements. Some useful alternatives to achieve compliance are using low frequency sounder bases, or connecting speakers to an in-building emergency voice alarm communication system.
In certain occupancies, low frequency alarms are a must. These devices can be the difference between life and death, especially for vulnerable or impaired populations. Meet NFPA 520 Hz requirements for sleeping room applications with our low frequency AV series: the Hochiki HHSLF Series, Gentex GHLF Series, System Sensor Low Frequency Sounders, and more. Low frequency sounder bases may also be used to satisfy NFPA standards and ensure the safety of your guests. Our collection of low frequency sounders and bases enables motels, hotels, universities, and apartments to effectively awaken guests and residents in the event of a fire or CO detection.
