Periodically security dealers and fire technicians write in to ask questions concerning what they believe to be a difficult problem. Some ask about fire alarms while others voice their concerns over security and access control. Most of the time the solutions they seek are simple; other times, not so simple.
This month, we’ll examine a couple of issues field technicians have written to me about the placement of projected beam smoke detectors and fire annunciators. (Note: Code references will be provided from NFPA 72, 2007 and 2010 editions. It’s important to provide both code references because most municipalities have yet to adopt the newer 2010 edition. Thus, at this time fire alarm installers and service techs are more likely to fall under 2007 or earlier.)
Projected Beam Smoke Detectors
These detectors are among the most difficult to understand where it comes to placement. According to Dave Winkler, system designer with Sentry Alarms of Binghamton, N.Y., “The manufacturers are so vague that the manual does not really help. Are there hard and fast formulas to help in locating the beams correctly? We’re using a single-ended System Sensor beam detector.”
A single-ended projected beam smoke detector uses an active light transceiver at one end and a reflective surface of some kind at the other. Compare this to a traditional two-ended detector that uses a light transmitter at one end and a light receiver at the other.
Winkler’s situation is not unlike many where a projected beam smoke detector can be used to cover a relatively large area. Common applications include warehouses; large, voluminous attics; long cathedral ceilings; and others.
“I’m working on a church sanctuary that’s 40 X 80 with 12-foot sidewalls and 22 feet to the peak,” he continued. “How do I figure the beam locations?”
Here is my reply to Winkler:
I’ll stick with 2007 NFPA 72 on this because most locales have not had time to adopt the new 2010. Section 184.108.40.206, titled Peaked, says that the first beam smoke must be installed 3 feet from the roof at the peak. This allows for stratification of course. At that point you would have to have two more, each within half the detection distance of each side wall.
In the case of the 6424 Projected Beam Type Smoke Detector by System Sensor, the effective detection distances are listed as 30 to 330 feet. That means you need to have each of the side units no less than 15 feet from the side walls. You will need three detectors for this application, which seems like overkill.
The 2010 version (Section 220.127.116.11) does not contain the 3-foot-to-peak rule. But the one thing that both editions do agree on is that you need to install a projected photo smoke detector according to the manufacturer’s instructions.
Not all manufacturers’ installation manuals are written in an ambiguous manner. In fact, there’s a fairly good explanation of how and where to install transceivers and reflectors in single-sided projected beam smoke detection systems out there, such as the Systems Sensor BEAM124(S) detector.
Fire Annunciator Placement
Some time back a fire technician who prefers to remain anonymous wrote in to ask about the placement of fire annunciators. In his situation, he was contracted to install a fully-addressable fire alarm system in a large industrial/office complex with multiple buildings.
His question was, “One of the buildings involves retail sales where the building is open to the public. Because we’re using a combination fire/burglar alarm panel, one listed by UL for commercial fire, we’d rather place the keypad in a protected area where members of the public cannot touch it.”
Inquisitive children are the most serious concern because of the various functions supported by an ordinary keypad. These functions include panic, hold-up, or duress; medical; fire alarm activation; plus, a variety of software-related functions. In some systems keypad function buttons also can be used to arm the system.
“The authority having jurisdiction [AHJ], however, says it must be in a readily accessible area of the building for firefighters when they arrive,” the inquiring reader added. “Do you have any information or suggestions on how to get the AHJ to change his mind?”
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