In a Flash: Installing Strobe Lights

By Wayne D. Moore | Dec 15, 2018

The performance, location and mounting of notification appliances used to inform, initiate or direct occupant evacuation or relocation is found in Chapter 18 of NFPA 72 2016, National Fire Alarm and Signaling Code. Fire alarm strobes have specific requirements based on room size and strobe output. As with audible notification appliances, strobe notification appliances must be designed to provide either public mode or private mode signaling.

The performance requirements for visible strobe appliances begin with UL 1971 so that designers, installers and authorities having jurisdiction only need to ensure strobes meet this UL standard.

It is the designer’s responsibility to document the rooms and spaces that will have strobes and those where there will be no strobes (e.g., hospital patient bedrooms). NFPA 72 does not require a system installation. The required coverage area for visible occupant notification shall be as required by other governing laws, codes or standards. However, NFPA 72 requires occupant notification by visible signaling high noise areas where audible signals would be ineffective. In occupancies such as healthcare facilities, the signaling is intended only for staff or emergency forces and will only need to be effective in specific locations, such as a nurse’s station.

Except for a few occupancies, such as healthcare and assembly use groups, you will be designing for public mode notification in all occupiable areas of the building. According to the code in Annex A, “The mounting height of the appliances affects the distribution pattern and level of illumination produced by an appliance on adjacent surfaces. It is this pattern, or effect, that provides occupant notification by visible appliances. If mounted too high, the pattern is larger but at a lower level of illumination (measured in lumens per square foot or foot-candles).

“If mounted too low, the illumination is greater (brighter) but the pattern is smaller and might not overlap correctly with that of adjacent appliances.

“A qualified designer could choose to present calculations to an authority having jurisdiction showing that it is possible to use a mounting height greater than 96 inches (2.44 meters) or less than 80 in. (2.03 m), provided that an equivalent level of illumination is achieved on the adjacent surfaces. This can be accomplished by using listed higher intensity appliances or closer spacing, or both.

“Engineering calculations should be prepared by qualified persons and should be submitted to the authority having jurisdiction, showing how the proposed variation achieves the same or greater level of illumination provided by the prescriptive requirements of the code ... .”

NFPA 72 2016 requires wall-mounted visible appliances to be mounted so the entire lens is not less than 80 inches and not greater than 96 inches above the finished floor or at the mounting height specified using the performance-based alternative described above and in Annex A. Where low ceiling heights do not permit wall mounting at a minimum of 80 inches, wall-mounted visible appliances must then be mounted within 6 inches of the ceiling. The room size covered by a strobe of a given value must be reduced by twice the difference between the minimum mounting height of 80 inches and the actual lower mounting height.

When spacing in rooms, the visible appliance must be in accordance with either NFPA 72 2016, Table and Figure or Table The visible notification appliances must be installed in using one of the following requirements:

“(1) A single visible notification appliance.

“(2)Two groups of visible notification appliances, where visual appliances of each group are synchronized, in the same room or adjacent space within the field of view. Synchronization of strobes includes those operated by separate systems.”

The strobe synchronization requirements do not apply where the visible notification appliances inside the building are viewed from outside of the building.

There are two methods of visible signaling. The first is where notification of an emergency condition is conveyed by direct viewing of the illuminating appliance. The second is by means of illumination of the surrounding area. The code requires public mode visible notification appliances to be located and of a type, size, intensity and number so the intended viewers see it regardless of their orientation.

As Annex A states, “Visible appliances for fire or emergency signaling might not be required in all rooms or spaces. For example, a system that is used for general occupant notification should not require visible signaling in closets and other spaces that are not considered as occupiable areas. However, a space of the same size used as a file room could be considered occupiable and should have coverage by notification appliances.”

My recommendation is to first design the fire alarm system for the audible devices to ensure code compliance and then design for the visible signal placement. Where you find there is one of each type of appliance near each other, change those units to combination audible/visible appliances. Never assume using combination units for the entire building is code-compliant. This method leaves some areas non-compliant for one type of appliance.

Bottom line, to be efficient and get a leg up on the competition, know and apply the code. Your own bottom line will improve as a result!

About The Author

MOORE, a licensed fire protection engineer, was a principal member and chair of NFPA 72, Chapter 24, NFPA 909 and NFPA 914. He is president of the Fire Protection Alliance in Jamestown, R.I. Reach him at [email protected]





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