Fire and smoke detection and signaling systems are proven to reduce fatalities among the general population during a fire. The optimum sound level that will be most effective and recognizable to occupants to signal evacuation has long been debated. At-risk populations of people such as school age children, the elderly, the hearing impaired or those impaired by alcohol or sleeping medication may not benefit fully from conventional smoke alarm systems, especially when sleeping. These groups of people can benefit from a low frequency smoke alarm signaling system.
Research
shows that low frequency tones are more effective than the 3,100 Hz higher
frequency tones commonly used in smoke alarms at waking people with hearing
impairments as well as people suffering with hearing loss. Audible evacuation signals of 520 Hz square
wave tone were effective at waking hard-of-hearing people in the study 92% of
the time.
Code Requirements
for Low Frequency Smoke Alarms
The National Fire Protection Association, NFPA, details
the accommodation requirements for low frequency fire and smoke alarms. NFPA 72, the
National Fire Alarm and Signaling Code, began to require that a temporal-three
sound produced at high frequency of about 3,150 Hz be used in building evacuation signals. Due to continued research, revisions were made to the
2010 NFPA72 edition, requiring low frequency smoke alarms at 520 Hz for single
and multiple station alarms or alarms which were not connected to a building
fire alarm where occupants are known to have a hearing impairment. Research over the last 20 years concludes
that these low frequency alarms are more effective at waking people who are
sleeping than the traditional alarms, especially people in high risk groups.
The 2013 edition of NFPA72 required all audible appliances
initiated by the building fire alarm located in sleeping areas to be at a low
frequency of 520 Hz. This broadened the
use of low frequency alarms although applied only to areas where the alarm is
intended to wake occupants sleeping and only when initiated by smoke alarms,
not by the building fire alarm system, in sleeping areas where people had mild
to severe hearing loss.
The 2021 edition of NFPA 101, Life Safety Code, makes the
use of low frequency smoke alarms much more consistent in all sleeping
areas. These most recent changes require
that when occupancy mandates the use, audible alarms in sleeping areas initiated by the building fire alarm
system or a smoke alarm must provide a low frequency 520 Hz alarm. NFPA 101 contains two residential occupancy
chapters for dormitories, hotels and new apartment buildings which are now
required to use low frequency alarms for audible notifications when initiated
either by both the building fire alarm system and smoke alarms.
The difference between the NFPA 72 and the 2021 edition of
NFPA 101 are that NFPA 101 now requires that all audible alarms in sleeping
areas initiated by smoke alarms be a low frequency 520 Hz regardless of the
hearing capabilities of occupants. NFPA
72 required low frequency smoke alarms only in areas where occupants had
hearing loss.
The challenge here is that a low frequency smoke alarm of 520 Hz requires extra electrical power which makes
battery operated alarms difficult. There
are a number of alternative solutions such as to use smoke detectors with
system horns, an integral sounder base or to connect speakers to an in-building
fire alarm EVAC system.
HRSS as your
fire and life safety security provider can design a code compliant
fire alarm system based on these most recent updates, your building and
occupancy. We offer comprehensive fire
and life safety services to commercial properties in and around Chicago. Contact us to learn more about building fire
and alarm requirements including low frequency smoke alarms.
This article was originally published at: https://hrsschicago.com/fire-alarm-systems/the-effectiveness-of-low-frequency-smoke-alarms/
