What is the minimum sound level at which visual notification appliances become necessary for effective warning?

Visual notification appliances are required to ensure that individuals who are deaf or hard of hearing can receive alerts in the event of a fire or other emergency when audible alarms may not be sufficient. The National Fire Protection Association (NFPA) standards, particularly NFPA 72, provide guidance for the placement and requirements of these devices.

The threshold of 105 dBa is established as the minimum sound level at which visual notifications become necessary. This is due to the understanding that as ambient noise levels rise, a corresponding increase in the probability that an audible alarm will not be heard or sufficiently recognized occurs. When sound levels are at or above this intensity, the alarm might effectively mask audible signals for some individuals.

Thus, at 105 dBa, visual notifications serve as a critical supplement to ensure that all individuals in a space are duly alerted to potential dangers, especially in environments with high ambient noise where the risk of missing an alarm is elevated. This standard ensures safety by addressing the need for all occupants to receive timely warnings, thus helping to prevent confusion during emergencies.