Duct Smoke Detectors and LED Test Plates

Duct smoke detectors are a common device found in most fire alarm systems from the past and present. Whether the duct smoke detector is addressable or conventional, they both work the same way. A sample tube is inserted into the duct work and samples the air for smoke. If smoke is detected then the photoelectric smoke detector head within the duct smoke detectors sends an alarm signal to the fire alarm panel and shuts down the air conditioning unit.

With that said, most of these duct smoke detectors are located in areas that are not very easily accessed. These areas could include areas such as above t-bar or hard lid ceilings, attic spaces or roof tops. If the actual duct detector is located above a ceiling then access hatches or panels must be provided for obvious reasons. Also if the duct smoke detector is located in an area out of sight then you must provide a detailed description of the device location within the fire alarm control panel program as well as a remote LED plate on the ceiling below the device. This will assist the fire department, end user and technician locate the device. In fact, some jurisdictions such as L.A. County are requiring the remote LED plate to be installed any time you have a duct smoke detector above a ceiling and out of plain view.

With all of this information it is hard for me to understand how some of these local fire alarm installation companies are getting away with installing the remote LED plates on the wall directly above the thermostat controls for the particular HVAC unit. This picture was taken at a local restaurant in the Valencia, CA area. Now with these remote LED plates installed on the wall it makes it easy for fire alarm testing but it totally eliminates their true purpose. If there is a fire reported at the building with a signal coming from a duct smoke detector then the fire department is going to want to know exactly where it's location is the minute they enter. The LED on the wall does not exactly help.