Strobes are essentially the only lights available for fire alarm notification. They have been misunderstood and even misused on occasion, but every fire alarm system with audible notification must have a complement of strobes to ensure the hearing-impaired occupants will be notified of an alarm.

The application and design guidance for strobes is in Chapter 18 of the 2016 National Fire Alarm and Signaling Code and is used for either public-mode or private-mode signaling. The code requires visible notification appliances used in the public mode to be located as required and be “of a type, size, intensity, and number so that the operating effect of the appliance is seen by the intended viewers regardless of the viewer’s orientation.”

Public mode is used when notifying all occupants in a building, and all occupiable spaces must have notification appliances. This pertains to both audible and visible notification appliances. However, the design of these two types of appliances have very different requirements. 

Most contractors that design their own systems simply make every notification appliance they use a combination horn/strobe. This is usually an incorrect decision because sound and light operate on different principles, which have specific code requirements. The code requires the designer to document all rooms and spaces where notification will take place by visible notification and defining those spaces where there will be no visible notification.

It is good design practice to document the effective intensity of each visible appliance on the drawings. The code allows the authority having jurisdiction to require submission of that documentation. 

Mounting height is important when using strobes, since it affects the distribution pattern and level of illumination produced by the strobe on adjacent surfaces. It is this pattern, or effect, that provides occupant notification by 
strobe appliances.

As stated in the Annex A of the code, “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.”

The goal is to ensure that hearing-impaired occupants see the flashing strobe and know an alarm is occurring in the building. The illumination provided by strobes is measured in candela and called “effective intensity.”

According to Annex A of the code, “effective intensity is the conventional method of equating the brightness of a flashing light to that of a steady burning light as seen by a human observer.”

The candela output of a strobe is provided by the manufacturer and marked on the appliance. These candela ratings are tested and listed by UL. The light output must comply with the polar dispersion requirements of ANSI/UL 1971, Standard for Signaling Devices for the Hearing Impaired, or equivalent. Because there are both wall- and ceiling-mounted strobes, it is important to ensure the strobes for each location needed are listed for that application.

The proper way to approach a notification appliance design for a fire alarm system is to lay out the audible notification appliances based on the sound level requirements for the space. Then, lay out the visible notification appliances based on the tables found in Chapter 18. The tables provide guidance for strobe placement in rooms and corridors based on the candela output of the strobe. Only then should it be determined where the two appliances are in the same area and where they can be combination units.

The code also provides guidance for low-ceiling applications where the strobe cannot be located at the required height on the wall. Essentially, they should be within 6 inches of the ceiling in those instances, but the marked or listed candela rating must be reduced by twice the difference between the minimum mounting height of 80 inches as specified in the code and the actual lower mounting height. Another option is to use listed ceiling-mount appliances.

Additionally, all visible signals must be synchronized to avoid causing seizures in those who may have photosensitive epilepsy. It is not required to synchronize visible notification appliances when the viewing locations are outdoors, nor is it required to synchronize the visible appliances between floors unless there is a visible coupling between the floors, such as an atrium.

Visible appliances are not required by NFPA 72 2016 except in high noise areas. The building codes, Life Safety Code, Occupational Safety and Health Administration, and Americans with Disabilities Act require these appliances. Also keep in mind that private mode signaling is only used where specific staff are notified rather than all of the occupants, for example, in hospital settings.

Knowing the code requirements helps ensure that a visible notification appliance design will be approved and also help to ensure an economically effective and profitable design.