Fire technicians at any skill level can find themselves in a situation where they do not know the answer to a particular problem. This month, we will discuss a few of the more notable questions that have come from the field during the past year.

Sensitivity Determines Replacement

This past summer, Stuart Glickman of Safe Alarm Systems wrote: “I have heard photoelectric smoke detectors in residential systems should be replaced at least every 10 years. Is there any documentation regarding this or do these detectors actually have to be tested for sensitivity?”

He also wanted to know if there are other ways to check smoke detector sensitivity, other than a one-size-fits-all calibration tester. This type of test can cost upwards of $4,500.

After examining National Fire Protection Association (NFPA) Document 72, 1999 Edition, the only reference I was able to find concerning smoke detector replacement involves the failure of one or more automatic smoke detectors to pass the required sensitivity test. Section 7-3.2.1, NFPA 72 states, “Detectors found to have a sensitivity outside the listed and marked sensitivity range shall be cleaned and recalibrated or be replaced.”

Exception 1 states that field-adjustable smoke detectors can be adjusted within the listed sensitivity range, in addition to cleaning and recalibration. The other option when these others have failed, or the client deems it necessary, is replacement.

The only reference to the replacement of detectors I could find in NFPA 72 involves heat detectors (Reference Table 7-2.2.13.d) where fixed temperature, spot-type detectors are to be tested. Here, code requires that after 15 years of service, all heat detectors must be replaced with new units. Or a quantity of these detectors must be removed and tested on the workbench for proper operation.

In this case, two devices out of every 100 must be removed and laboratory tested. If any of these heat detectors fail the test, then additional detectors must be removed from the job site and tested in the same manner. Of course, heat detectors that are removed must be replaced with new ones.

Methods to Test Smoke Detectors

To address the same dealer’s concern about the relatively high cost associated with a one-size-fits-all calibration tool, let us first cover the three basic ways dealers can test their clients’ smoke detectors for sensitivity. They are:

1) A special tool specific to a given model and make detector, usually included with each detector.

2) Plug-in sensitivity tester specific to a given make and model detector.

3) A one-size-fits-all tester that can be used on anyone’s smoke detector.

The first method involves the use of a special go/no-go tool a fire technician inserts into the body of a smoke detector. When inserted in one direction, the detector will indicate a trouble condition, akin to when a smoke chamber has become dirty. When inserted the other way, the detector should go into alarm.

The downside to method two, a plug-in tester, is that although the cost is generally less than the one-size-fits-all model, the fire technician can only use it on one manufacturer’s line of smoke detectors. For dealers who expect to take over a competitor’s inspection work, you would have to have a test tool for every possible make/model you might encounter – which can be cost-prohibitive as well.

There was a day when dealers used a box tester that enabled them to insert the smoke detector in question for a general smoke test. That method is no longer valid as NFPA 72 now calls for all tests to be conducted with the smoke detector in place. In other words, a smoke detector is to be checked while it is mounted in its working location.

“The detectors shall be tested in place to ensure smoke entry into the sensing chamber and an alarm response” (NFPA 72, Table 7-2.2[g][1]).

The above three methods of checking smoke detector sensitivity are the most generally accepted methods in use today, but there may be others. Always check with the smoke detector manufacturer as NFPA 72 often defers to the manufacturing firm’s recommended method(s) of testing.

Mathematics of Sizing Up a UPS

A reader responded to my November column (“Averting Battery and PBX Hazards”) by requesting a little math to go with the sizing of an uninterruptible power supply (UPS) system. A colleague of mine, John Pecore, president of Stormin’ Protection in Pinellas Park, Fla., says 50VA are required on startup when sizing a new UPS.

“Then, here is the real trick. On a switch-mode power supply, which is what most computers have, you would be done with the calculations. Not with a PBX or interconnect equipment. They have a linear power supply.  Guess what? They pull one-third more VAs,” says Pecore.

Let’s expand on this concept. Calculate one-third of the VA value and add it to the total. If your PBX draws 6A at 115V, multiply this by line voltage (use 115VAC) and add 50VA on startup, as follows:

1) 115VAC X 6A = 690VA.

2) Add another 50VA for start up = 740VA.

3) 1/3 of 740VA = 246.67VA.

4) Add 740VA + 246.67VA = 986.67VA.

“This calculation provides a total of 15 minutes of run time once the electricity has failed. Now, if you want an hour of run time, you must multiply this figure by four,” Pecore adds. Observe, 986.67VA X 4 = 3945.68VA. Get the idea?

Know Your Fire Technology Terms

As the fire industry advances, so does the ratio between the use of multiplex vs. conventional fire technology. Because the proliferation of multiplex on the horizon is considerable, it is essential fire technicians understand the common terms employed by the NFPA when working with multiplex and conventional initiating device technologies.

I am often asked what is the best way to become familiarized with these terms. One way is to refer to the definitions set forth in NFPA 72, the National Fire Alarm Code, including the following found in the association’s print and CD-ROM-based materials:
Active multiplex system – multiplexing system in which signaling devices such as transponders are employed to transmit status signals of each initiating device or initiating device circuit within a prescribed time interval so that lack of receipt of such signal may be interpreted as a trouble signal.

Addressable device – fire alarm system component with discrete identification that can have its status individually identified or that is used to individually control other functions.

Analog initiating device (sensor) – initiating device that transmits a signal indicating varying degrees of condition as contrasted with a conventional initiating device, which can only indicate an on/off condition.

Initiating device circuit – circuit to which automatic or manual initiating devices are connected where the signal received does not identify the individual device operated.

Multiplexing – signaling method characterized by simultaneous or sequential transmission, or both, and reception of multiple signals on a signaling line circuit, a transmission channel, or a communications channel, including means for positively identifying each signal.

Signaling line circuit – circuit or path between any combination of circuit interfaces, control units, or transmitters over which multiple system input signals or output signals, or both, are carried.

Signaling line circuit interface – system component that connects a signaling line circuit to any combination of initiating devices, initiating device circuits, notification appliances, notification appliance circuits, system control outputs and other signaling line circuits.

Supervisory signal – signal indicating the need of action in connection with the supervision of guard tours, the fire suppression systems or equipment, or the maintenance
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