Directional Sounders Part II - Code Requirements and Applications

Last month’s issue featured the first article in a series about exit marking directional sounders, in which we discussed the purpose of these new devices, explained their development and covered the basic acoustic principles on which they operate. This month’s discussion goes a step further in defining their application.

The horns/strobes/speakers normally tied into a commercial fire alarm system are the code-required notification (located per NFPA 72) audible and visible appliances used to alert a building’s occupants for the need to evacuate or relocate within the building. Any device or appliance that is not required by a code or standard is called “supplemental.” One example includes directional sounders, which are not a replacement for the code-required audible or visible notification appliances, but instead are designed to be blended into the standard audible warning produced by horns, bells or the voice evacuation message produced by speakers.

Supplemental also means that directional sounders must be “sold” to the building owner or tenant and proposed for their consideration as an improvement to evacuation efficiency in specific circumstances.  In some cases, directional sounders are not always useful or desirable. For example, leading large numbers of occupants toward exits that cannot accommodate such a large group at one time would certainly not enhance evacuation efficiency. Each installation must be evaluated as to their applicability, based on the manufacturer’s documentation and installation instructions.

Being a “supplemental” device doesn’t mean the code is silent on these directional notification appliances. Section 7.4.6 of NFPA 72 provides the five basic requirements for directional sounders.

“7.4.6 Exit Marking Audible Notification Appliance Requirements.
7.4.6.1* Exit marking audible notification appliances shall meet or exceed the frequency and sound level settings and guidelines specified in the manufacturer’s documented instructions.
7.4.6.2* In addition to 7.4.6.1, as a minimum, to ensure that exit marking audible notification appliance signals are clearly heard and produce the desired directional effects for 15.24 m (50 feet) within an unobstructed egress path, they shall meet the audibility requirements of 7.4.6.1, Narrow Band Tone Signaling for Exceeding Masked Thresholds, in at least one octave band or one octave band within the effective frequency ranges of the interaural time difference (ITD), interaural level or intensity difference (ILD or IID) and anatomical transfer function or head-related transfer function (ATF or HRTF) localization cues. The signal shall penetrate both the ambient noise and the fire alarm signal.
7.4.6.3  Where required, exit marking audible notification appliances shall be installed in accordance with the manufacturer’s instructions.
7.4.6.4*  Where required, exit marking audible notification shall be located at the entrance to all building exits and areas of refuge as defined by the applicable building or fire code.
7.4.6.5 Where exit marking audible notification appliances are utilized to mark areas of refuge, they shall provide an audible signal distinct from that used for other exits that do not have areas of refuge.”

Additional directional sounders may be wired into either a new or an existing notification appliance circuit [can be added to most two-wire NACs] for systems using standard 24 volt DC regulated power supplies (not FWR), keeping in mind that the same NAC wiring rules apply.

Additional installation requirements  may include obtaining a permit, submitting plans indicating the location of all notification appliances, and providing specification sheets for all the existing and new appliances, as well as voltage drop and standby battery calculations.

For a basic Type 1 system/installation, look for the illuminated exit signs in public buildings. Type 2 installations consist of a typical Type 1 installation but include additional sounders to provide an audible indication of the best egress path to lead occupants to where they will hear the Type 1 directional sounder located at exit/refuge areas.