Chapter 18 of NFPA 72, National Fire Alarm and Signaling Code, contains the requirements for audible and visible notification appliances. This subject is often confused by designers, contractors and authorities having jurisdiction (AHJs) because the performance for each type of appliance is treated differently in individual locations.

This article focuses primarily on the audible notification appliance requirements and a new notification mode that has been added to the 2025 edition of the code.

The most common audible notification mode is public. It should be obvious that this mode means everyone in the building should hear the alarm signal. Specifically, the sound level must be 15 decibels (dB) above the average ambient sound in every space in the building where the public resides. The code also allows the sound level to be 5 dB above the maximum sound level having a duration of at least 60 seconds in the space where measurements are made. All sound level measurements for the public mode of notification appliance operation must be measured using a calibrated sound level meter, using the A-weighted scale (dBA), with all measurements made 5 feet above the finished floor in all occupiable spaces.

Private mode audible requirements allow for sound levels to be diminished to 10 dB above average ambient sound levels, with the same allowance for 5 dB above the maximum sound level having a duration of at least 60 seconds in the space where measurements are made. 

Typically, private mode signaling is used in healthcare occupancies. Because staff are present 24/7 and patients are not typically mobile, the code allows private mode primarily for alerting staff, so they can take the necessary action for patient safety. In critical care patient areas, it is often desirable to not have an audible notification even at reduced private mode levels. 

Additionally, there are high-noise work areas where the audible signal needed to overcome background noise at one time of day would be excessively loud and potentially dangerous at another time of lower ambient noise. A sudden increase of more than 30 dB over 0.5 seconds can cause sudden and potentially dangerous fright. Each case of a change in alarm notification from the prescribed code requirements will necessitate consideration by the governing authority. Although this mode of signaling will require AHJ approval, it makes no sense to use public mode signaling in these applications.

Although not given a mode designation, there are specific requirements for sleeping areas. The code states that where “audible appliances are installed to provide signals for sleeping areas, they shall have a sound level of at least 15 dB above the average ambient sound level or 5 dB above the maximum sound level having a duration of at least 60 seconds or a sound level of at least 75 dBA, whichever is greater, measured at the pillow level in the area required to be served by the system using the A-weighted scale.” 

If there is a barrier, such as a door, curtain or retractable partition, between the alarm notification appliance and the pillow, you must measure the sound level with the barrier in place. All notification appliances used to awaken occupants in sleeping areas must produce a low-frequency sound as described in Section 18.4.6.3.

Restricted audible mode operation

The new twist in the 2025 edition of NFPA 72 is a restricted audible mode operation (RAMO) notification. The requirements for using the RAMO notification must be determined by a risk analysis of the notification zone or with the AHJ’s approval. Allowing RAMO is intended to accommodate areas where loud signals might be detrimental to occupants of the notification zone, such as early education classrooms or facilities used by people with “other conditions that might include sensitivity to light, noise or other stimuli.”

Specific requirements for RAMO areas include the following:

• RAMO areas must be indicated on the project drawings.
• RAMO will only be permitted where trained, awake and mobile staff are present.
• All audible devices must be low-frequency.
• All audible notification appliances must be synchronized.
• All visual notification appliances must be synchronized.

As you continue to install fire alarm systems, you will experience more requirements for risk analysis. In the long run, these will help ensure the systems you install are operationally reliable for the occupancy involved. By knowing the current code requirements, you will have a leg up on the competition.

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