NFPA 72 and You
By Zach Perry
You’re probably thinking to yourself, “Self, why am I reading this?” You googled Fire Alarms for Elevators and stumbled here. There you are, bleary eyed, confused, and hoping for fire alarm answers for your new elevator. You’re getting 17 directions for elevator alarms and the oddities they entail. With NFPA 72 2019 and newer, there were some updates that snuck under the radar for some. Here, ATIS will try to dispel some of the issues you may have run into.
2019 NFPA 72 updated the requirements for fire alarm initiating device (FAID) to include the language stating FAID must be accessible from outside the hoistway. This was a departure from previous codes, that allowed standard spot type smoke and heat detectors in the hoistways. This was likely due to many reasons, such as the main hazard area for an elevator is the hoistway and FAID are typically installed in hard to reach areas, increasing the hazard. Also, paying for the elevator contractor to access these areas is expensive for maintenance purposes of these items.
First, let’s establish some basic FAID requirements that are affected by this new rule.
A smoke sensor is required in top of the hoistway for a machine roomless elevator (MRL).
A means to remove power from the elevator prior to the application of water from a sprinkler (called shunt trip). This is typically a heat sensor within 24” of the sprinkler head but can also be an inline flow switch in the sprinkler line. This is only for sprinklers in elevator equipment areas (pits, hoistways, machine/control rooms, etc. ) and does not typically apply to sprinklers in the lobbies.
Smokes and heats shall be installed in pits of hydraulic elevators that have sprinklers.
Sprinklers are required in the pits and machine rooms of hydraulic elevators and hoistway of some traction elevators that use non-fire rated hoisting belts. Where sprinklers are installed in the pits, shunt trip is typically required, though there is an exception for the pit location only. If the application of water will not cause unsafe elevator operation, the pit sprinkler does not need shunt tripped. ATIS has not crossed a manufacturer willing to provide documentation to this effect, so we require shunt tripping of sprinklers in pits.
So, you have to have FAIDs in the hoistway but you cannot access them. What are the options? For smoke sensors, an aspirating smoke detector is typically provided. This samples the air in the hoistway through a series of tubes permanently routed in the hoistway. The system vacuums air through the tubes, which have small air holes for sample collecting. Once smoke is present, it activates the smoke detector and a signal is sent to the elevator to recall, as a fire in the elevator area has been detected.
Shunt trip activation has linear heat detectors, in lieu of traditional spot heat sensors. The brains of the system are mounted outside of the hoistway, and a thermocouple is run into the hoistway to sense temperature. Once the temperature hits a predetermined number, the sensor activates and removes power from the elevator.
Linear heat detectors have an issue that may not be realized until installed. NFPA 72 requires the detector to be within 24” of the sprinkler head and a loop within 24” of the head complies. The issue is, the rest of the detector is not within 24” of the head. The thermocouple will monitor the temperature along its entire length. This means a fire more than 24” from the sprinkler may activate the heat sensor, remove power from the elevator (possibly entrapping someone) and never activate the sprinkler to put the fire out. Due to this scenario, ATIS highly recommends running the thermocouple in conduit. The conduit shall be open on the sprinkler end, with the end of the conduit being within 24” of the sprinkler, and a loop of the thermocouple sticking out the end. This is above what is required by code, but reduces the risk to life while providing the operations required by the codes.
If you need help deciphering NFPA 72, ATIS is here to help.