Placement. Ceiling-mounted appliances are not permitted by the ADAAG, but are permitted by NFPA 72. It is not always possible to provide complete coverage for large open areas using perimeter-mounted appliances because of the limited appliance ratings available. Table 4-22.214.171.124(b) of NFPA 72 addresses ceiling-mounted visible notification appliances and is valid for ceilings up to 30 feet in height. If the ceiling is more than 30 feet in height, pendants must be used to bring appliances to a minimum of 30 feet above the finished floor. Section 4.28.3 of the ADAAG permits ceiling-mounted notification appliances where there are no obstructions in the open area over six feet high. In this case, the appliances must be spaced not more than 10 feet apart.
Typical big box warehouse stores can be especially challenging because the commodity racks prevent direct viewing of the appliances by shoppers. In this case, each aisle must be treated as a corridor. Forklifts can also cause mechanical damage to the appliances. Mechanical protection should always be used in these cases. Additionally, it often takes a great number of appliances to cover an entire store.
Non-sleeping areas. The ADAAG and NFPA 72 have differing requirements for the mounting height of visible notification appliances. The ADAAG requires visible notification appliances to be mounted at least 80 inches above the finished floor, or six inches below the ceiling, whichever is lower. Section 4-4.4 of NFPA 72 requires visible appliances to be mounted such that the entire lens is between 80 and 96 inches from the finished floor. There is some overlap of the mounting height ranges, and mounting appliances in this range can satisfy both ADAAG and NFPA 72. It should be noted that NFPA 72 requires visible notification appliances to be mounted in the mounting heights as they are tested in the laboratory. Mounting them higher will attenuate the signal, which reduces the effectiveness of the appliance.
Sleeping areas. Sleeping areas present unique signaling challenges. Both NFPA 72 and the ADAAG require the visible signaling to be of sufficient intensity to wake a sleeping person. Section 4-126.96.36.199 of NFPA 72 requires a minimum 110-candela appliance to be mounted on a wall not less than 24 inches from the ceiling, or a 177 cd appliance if mounted less than 24 inches from the ceiling. The higher intensity is required in case there is a smoke layer, which could attenuate the signal. The appliance must be mounted not more than 16 feet from the pillow when room dimensions exceed 16 feet in any direction. Mounting heights for sleeping areas are the same in NFPA 72 and the ADAAG.
The ADAAG permits either a visible notification appliance or a tactile (vibrating) appliance for waking a sleeping occupant. NFPA 72 also permits tactile appliances, provided they are listed for this purpose, as required by Section 1-5.1.2. But there are currently none listed for this use. Therefore, a visible appliance is one of the only ways of satisfying both ADA and NFPA 72.
Rooms designated for the hearing impaired must be outfitted with a smoke alarm that has a visible signaling device as described above. Note that smoke alarms must be mounted within 12 inches of the ceiling or on the ceiling, so be sure they are provided with a 177 cd notification appliance. Some smoke alarms can be installed such that the integral strobe can be triggered by the building fire alarm system to provide warning of a building-wide alarm. Other approaches may rely on separate system-powered notification appliances in addition to the smoke alarm/integral notification appliance arrangement.
Synchronization. Flash rates of about four cycles per second (4 Hz) may adversely affect people with photosensitive epilepsy. Composite rates caused by more than two strobes in a single field of view can generate strobe rates in excess of this value, which may lead to an epileptic seizure. Nonetheless, notification appliances in large areas and within a common field of view require synchronization by NFPA 72 to prevent seizures.
The effect on photosensitive epileptics drops off quickly after about 55 feet. Most manufacturers have developed modules that synchronize visible notification appliances. Generally, it is best to use fewer high-powered visible notification appliances. This not only reduces installation costs, it can also eliminate the need to synchronize.