Fire Alarm Notification Delay from Sprinkler Waterflow

Over the past several months, I have noticed a few incidents occurring in mercantile occupancies that have raised some questions related to the allowable delay between sprinkler activation and fire alarm notification in the event of a fire, which is governed by NFPA 72®, National Fire Alarm and Signaling Code®.

One example is a video of this fire in a Maryland Walmart. The video was taken by an occupant inside the building as they are exiting the building and shows sprinklers operating and controlling the fire. You notice that there is a time delay between the activation of the sprinklers and the activation of the occupant notification within the building. Many people are asking the question, why doesn’t the fire alarm immediately warn the occupants that there is a fire in the building as soon as the sprinklers activate?

The answer is that NFPA 72 permits up to a 100-second delay between sprinkler waterflow and occupant notification, as you can see at the end of the video, the fire alarm did activate the occupant notification via audible and visual notification.

The allowance for a 100-second delay before the actuation of alarm notification appliances is broken down into two requirements. The first requirement is related to the waterflow initiating device and found in section 17.13 of the 2022 edition of NFPA 72. 17.13.2 requires that the waterflow initiating device activate within 90 seconds after a flow occurs that is equal to or greater than the flow from a single sprinkler of the smallest orifice size.

The 90-second allowance exists to reduce the number of nuisance alarms caused by water flow that can occur from pressure surges in the water supply system and allows time for the flow from a sprinkler in the system to be detected at the riser. The delay provides added assurance that the water flow in the sprinkler piping is in fact sustained flow from a sprinkler, and not just the result in a change in pressure. The reduction of nuisance alarms is important because a fire alarm system that has many nuisance alarms can cause the occupants to become complacent and may begin to ignore the fire alarm.

This delay in the water flow switch activation can be created within the flow switch itself using a retard dial, or it can be accomplished with the use of a retarding device such as a retard chamber when using a pressure switch that is connected to the alarm port on a sprinkler system alarm valve.

The second part of this delay is found within section 10.11.1. This section requires that the actuation of alarm notification appliances at the protected premises occurs within 10 seconds after the activation of the initiating device. This requirement exists to ensure that the operation of the notification appliances occurs within a timely manner after a fire has been detected. Between those two requirements in section 17.13.2 and 10.11.1, NFPA 72 permits up to a 100-second delay between the initial waterflow from a sprinkler and the actuation of the notification appliances within the building.

In addition to this allowance intended to reduce the number of nuisance alarms, allowances exist to delay the actuation of notification appliances for other initiating devices with the use of a presignal feature or positive alarm sequence, though both require a detailed response plan and approval from the authority having jurisdiction.

The next time someone asks you a question about the timing of sprinkler waterflow and fire alarm notification, remember that NFPA 72 permits the delay in the actuation of fire alarm notification appliances. This timing is engineered into the operation of the systems, and it exists to ensure that they function as effectively as possible and reduce unwanted nuisance alarms.

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Shawn Mahoney
Technical Services Engineer with a masters degree and PE in fire protection supporting subjects throughout the association

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