control manufacturer. If you choose wall-mounted strobes and have es-
tablished the base design, you may now begin to evaluate their locations
to determine where the combination audible/visible units might serve
If you choose to use ceiling-mounted notification appliances as a
performance alternative, know that the effectiveness of ceiling-mounted
appliances does not depend on them being mounted on a surface. Therefore, the code permits you to suspend them below the ceiling, using proper
electrical installation methods.
Appliances mounted parallel to the floor, whether on a ceiling or suspended, can sometimes significantly reduce installation costs and provide
better coverage. The code provides alternative information for ceiling-mounted notification appliances when ceilings exceed 30 feet. In those
instances, you must either choose to suspend ceiling-mounted visible
notification appliances at or below 30 feet, install the ceiling-mounted
appliances at the mounting height determined using the performance-based
alternative of Section 18. 5. 5. 6, or install wall-mounted visible notification
appliances in accordance with Table 18. 5. 5. 4. 1(a).
As with the use of low-frequency audible appliances for sleeping ar-
eas, the code provides special requirements for strobes when used to
awaken sleeping individuals. For this application, consult Table 18. 5. 5. 7. 2
to determine the minimum required intensity.
The code states: “Where the appliance is mounted less than 24 in.
from the ceiling, it must have a minimum 177 cd effective rating because
it might be in a smoke layer at the time it is called upon to operate. If the
appliance is 24 in. or more from the ceiling, it is permitted to be rated
110 cd effective or more. Note that the requirement for increasing the
intensity when mounted close to the ceiling applies only to strobes used
in sleeping areas to awaken sleeping people. It is assumed that in non-
sleeping situations, a strobe is not needed to alert someone if there is a
developing smoke layer.”
When strobes are used in MNSs, they cannot have any “fire” marking
but they may be marked with the word “alert” stamped or imprinted on
In addition to strobes used as visible notification appliances, the code
permits the use of “textual” and graphical visible notification appliances.
Textual visible appliances may consist of scrolling message boards or flat
screens. Static signs serve as one example of graphical visible notification appliances. Typically, MNSs will have the largest amount of textual
visible appliances. Chapter 24 permits the use of textual and graphical
visible notification appliances for primary or supplemental notification.
The code considers textual and graphical visible notification to serve
as a means of primary notification where it provides the only method
used to convey emergency mass notification information to the general
public or specific individuals. Chapter 24 requires that, when audible
notification is provided, the MNS must also provide visible notification
information to serve the hearing impaired and for high-noise areas. Additionally, Chapter 24 permits the use of textual and graphical visible
appliances for nonemergency purposes; however, the code requires emergency textual and graphical messages to override nonemergency textual
and graphical messages.
Although this article does not provide an exhaustive account of the
visibility and audibility requirements found in the code, it serves to make
designers aware of the importance of understanding the underlying performance requirements and objectives of the two methods of alerting
individuals in buildings.
MOORE, a licensed fire protection engineer, frequent
speaker and an expert in the life safety field, is a principal
member and past chair of NFPA 72, Chapter 24. Moore is
a vice president with Jensen Hughes at the Warwick, R.I.,
office. He can be reached at firstname.lastname@example.org.
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