During the MCFP Virtual Conference series, expert Lee Kaiser, covers air sampling smoke detection. In the video below, watch as Lee dives in-depth for what goes into air sampling smoke detection and how to test it.
air sampling smoke detection systems
Many people in our audience are users of air sampling smoke detection systems like Vesda. If you're a Vesda user, the code says you need to follow the manufacturer's methods for testing. They don't give a ton of information on the methods inside the code, but generally all the manufacturers of air sampling smoke detection equipment agree that there needs to be an alarm response test and a transport time test.
Alarm response is, does it activate, does it sense smoke and does it send a signal to the fire alarm panel? That's the alarm response piece. For the transport time test you need to understand how an air sampling smoke detector works, and so we've got a picture of a Vesda unit here. It's a box that would get installed on a wall and out of the top of that detector, we would run ¾-inch CPVC pipes, those orange Blaze Master pipes out of the detector and out into the space. Those pipes fan out in the room and then holes get drilled in those pipes that need to be able to suck back air from the room, through the pipes, back to the detector. The detector has a little fan in it providing suction to those pipes. When we draw air from the room, through the holes, back through the pipes to the detector and then inside the detector we look at the air that we're bringing back to the detector and we see if there is smoke in it and we measure how much smoke there is.
The code says we have a maximum time that we're allowed to let the air bring smoke back to the detector, and so we do a transport time test. From the furthest away hole we introduce a little bit of smoke and then we time with a stop watch how long it takes for smoke to register at the detector. We have a maximum of 120 seconds, and some installations have even shorter times that are required for those customers.
There is an option with some of our newer installations where we're using an alternative method called a benchmark test point. This is a testing point that gets intentionally installed at the end of a system. It's normally a closed point, not an open hole, but we locate it where it's easily accessible and then once a year for annual testing, the hole opens up through a little valve that's part of the benchmark test point. We introduce a little bit of smoke there and then we have written the performance expectations that we had from the last time including the transport time test from that location and the suction pressure. We measure the suction pressure using that same digital monometer that we referred to in the duct detectors testing.
When we measure that we can then see from those readings if there are any changes in that pipe network. Even if we can't see the entire pipe network, we can sense if there's a negative change that may have occurred and then we do further investigations and rectify that condition.
The last thing that we need to do, if the manufacturer says, is to verify airflow through all the ports. Most detectors are automatically arranged to do that through airflow sensing. So, each pipe coming back to the detector has a little airflow sensor in it and if it sees a reduction in airflow we automatically know that there's a problem. This generates a fog condition, which shows up as a trouble on the panel and it's self-supervising for airflow.