There is one case when you are specifically requested to use a heat detector. A "shunt-trip" has been required since the 1984 edition of ASME A 17.1. This shutdown is intended to stop the elevator prior to any sprinkler head's water spray from reaching the car's electronics, brakes or machine room equipment.
Since NFPA 72 doesn't prohibit a smoke detector in sprinklered hoistways, a smoke detector may sometimes be specified to initiate Phase One Recall to deliver any occupants to safety before this shunt-trip occurs. Since this shunt-trip has caused so much concern, some recent developments in shunt-trip controls now allow the car to travel to the safe level and open the doors before causing the car to stop all operation.
It is permitted to use a waterflow switch (without a retard delay) to perform the shunt-trip. Unwanted recalls from water surges should not be a concern since the vane- type waterflow switch is installed within only a few feet of a sprinkler head. However, the required waterflow tests and inspections can be a big problem involving elevator technician licensing/permits and personal safety.
Only the automatic detectors located in elevator lobbies, hoistways and machine rooms are permitted to initiate the recalling of elevators. In no case should an elevator be recalled by a manual pull station or by detectors located in other areas of the building.
Greg Kessinger, SET, CFPS, president of an alarm installing company since 1981, teaches NICET training classes to fire alarm system designers and installers and continuing education seminars for Ohio's fire alarm inspectors. You can reach Greg Kessinger at 888-910-2272; e-mail: Greg@firealarm.org; or visit his website at www.FireAlarm.org.