Updated: Dec 8, 2021
Most states base their elevator regulations on ASME A17.1, Safety Code for Elevators and Escalators. In many cases, a sprinkler is required in the bottom of an elevator pit. When a sprinkler is installed, NFPA 72, Fire Alarm Code, and ASME A17.1 require elevator hoistway pits to be protected via fire detection devices.
Elevator hoistway pit detection poses a unique challenge for several reasons. The elevator pit is considered a harsh environment because of the potential for dust, dirt, and humidity. Over time, standard spot-type smoke detectors are prone to false alarms. The elevator pit is a location that is extremely difficult for functional testing of devices as required by NFPA 72. In some states, such as Massachusetts, sprinklers are not permitted in elevator shafts. When sprinklers are not installed in elevator shafts, NFPA 72 prohibits the installation of smoke detectors.
In sprinklered elevator shafts, heat detectors are required to be installed within twenty-four (24) inches of each sprinkler in the pit. The heat detector needs to have both a lower temperature rating and a higher sensitivity than the sprinkler. The design goal is to ensure that power is interrupted to the elevator prior to sprinkler discharge.
The smoke detector in an elevator pit plays an important role in elevator passenger safety. It is intended to successfully recall the elevator prior to elevator shutdown. Proper location and selection of initiating devices are key to minimizing the likelihood of passenger entrapment between floors. To achieve this, it is important to detect a fire in the elevator pit as soon as possible. A smoke detector detects the early signs of a fire before it generates significant heat.
While not currently in force in most jurisdictions, NFPA 72, 2019 edition introduces an additional requirement that initiating devices installed in the elevator hoistway must be accessible for service, testing, and maintenance from outside the elevator hoistway.
An ideal detection solution for an elevator pit is one that is compliant, effective, easily maintained, and economical.
For heat detection, a linear type detection wire can be used within the elevator pit to detect a fire. Linear heat detectors are functionally tested by shorting the end-of-line resistor. To ensure compliance with NFPA 72 and ease of testing, the junction box containing the end-of-line resistor should be located outside the elevator pit, preferably in the elevator machine room.
While the approach for heat detection is straightforward, heat detection is a bit more challenging. Air sampling smoke detection is a method of smoke detection where the physical detector is located remote from the protected area and a fan (aspirator) actively samples air from the protected area via a network of CPVC piping. There are full function air sampling detectors available that could certainly provide effective elevator pit smoke detection; however, this approach is typically cost-prohibitive. There are also air aspirating spot-type smoke detectors available that are listed for harsher environments such as an elevator pit. These spot-type air aspirating detectors can provide a cost-effective means for elevator pit smoke detection.
A key design consideration is including routing a test port back into a space containing the detector so that testing can occur without entering the shaft. It is also important to ensure a return pipe is routed back to the elevator pit so that after being sampled, air can be returned to the pit. In pits where high humidity may be present, providing a condensate drain leg within the sampling network should be considered.
F&T has successfully leveraged linear heat detection and spot-type air aspirating detection to provide owners with thoughtful, practical fire alarm solutions for elevator pits. Contact us today to learn more about how we can help you.
Fire Protection Project Engineer