Fire alarm activation from 2 devices?

Hi, I work at an industrial facility with a double-interlocked pre-action fire protection system. In order for the riser pipes to fill with water, not only must air pressure drop (sprinkler head release), but the device solenoid must initiate. For most zones, those solenoids are also double-interlocked—they’ve been programmed so that two devices (smoke, heat etc) must go into alarm before the solenoid valve will release.

To reduce the number of false evacuations/alarms, I’m considering a possible programming change to our EST fire alarm system: reprogramming the fire alarm (horns/strobes) so that it is also double-interlocked (requires two devices to initiate before signaling the building alarm). I haven’t yet spoken to our AHJ, but I’m wondering if there’s any obvious code restriction that would prevent this change (i.e. NFPA says the alarm must initiate from any single ONE device). Also, does anyone know if there’s any precedent to that kind of double-interlocked fire alarm arrangement?


Anything can be done - with AHJ approval. And your local AHJ can override anything in NFPA. So I wouldn’t worry about satisfying code as long as you satisfy the AHJ. One thing to consider, he is probably not going to grant you that change just because it sounds like a good idea. You should demonstrate some hardship that happens when the alarm is activated (financial loss, overburdening the fire department, etc). Also, you didn’t specify what the degree of hazard your industrial facility. Do you make gasoline and matchbooks or concrete railroad ties - a higher degree of hazard may require a more immediate response. Have a good safety/evacuation plan in place before you present you case. In other words, have all your ducks in a row. If you are having problems with false alarms, make sure you are on top of maintenance. Having the fire alarm tested on an annual basis, cleaning detectors, checking sensitivity - all things that can help find problems before they are problems.

Now, is it possible - sure! We have a local mall that has total fire alarm coverage throughout (smokes, heats, duct detectors) including inside the tenant spaces. They were plagued with false alarms. Construction, water leaks, dirty devices, you name it. It becomes a problem evacuating a shopping mall every couple of weeks. And the fire department starts sending out fines. So they came up with a solution:

1.) All smokes, heats, and duct detectors will report to the FACP as a supervisory first. Mall security has 60 seconds to acknowledged the event via a button at the security desk. If they do not acknowledge the event in 60 seconds, the mall goes into full evac.

2.) After the supervisory is acknowledged with the button, they have two minutes to investigate the incident. If it is a fire, there is a manual pull station at the guard desk that will put the mall into full evac. If the two minute timer expires and they have not re-acknowledged the signal, mall goes into full evac. They can continue to acknowledge the signal as many times as needed.

3.) There is only one other pull station in the building, but any other pull station, waterflow, or kitchen hood activation will put the mall in an immediate evac alarm (there is no 60 second delay).

As far as I know, this has worked for them to reduce false alarms. So again, not knowing fully your situation, if you had on site 24/7 security, this could be something that might work for you.

“Cross zoning” used to be very popular for false alarm prevention when detectors weren’t intelligent, you should have no problems switching to that arrangement however the AHJ might require more devices to be added to have better coverage. I was in a large office building recently that had this set up, the catch was they had to have at least two smokes in every room so there were two devices to activate the alarm.

As you’re already aware, cross zoning is already a standard for releasing systems.

You may also look at just upgrading your smoke detectors, if they’re really old EST may have newer ones that are less vulnerable to false alarms.

Here are some other nuisance alarm prevention techniques. These suggestions already are included in NFPA 72. However they do require approval by the AHJ.

If you problems are mainly caused by smoke detectors after cleaning, sensitivity testing, or replacement you could try adding Alarm Verification to the system.

In system generated Alarm Verification the first activation of one smoke detector does not show an alarm on the panel. The system then resets that detector. A confirmation period starts in which if that detector alarms again the system goes into evacuation mode. Any time during this sequence if a second device of any kind activates the verification sequence is cancelled and the system goes into evacuation mode. If that detector or any other device does not activate during the confirmation period the system times out and restores to its normal standby mode. Some systems maintain a verification tally and/or make an event log entry so detectors activating frequently are flagged so they can be serviced or replaced.

If your facility and fire alarm panel are constantly attended by security personnel, you could apply to use Positive Alarm Sequence. Here is the description from NFPA 72 2007 and an on line article. Alarm verification cannot be combined with positive alarm sequence. Positive Alarm Sequence. Systems that have positive alarm features complying with shall be permitted if approved by the authority having jurisdiction. The signal from an automatic fire detection device selected for positive alarm sequence operation shall be acknowledged at the fire alarm control unit by trained personnel within 15 seconds of annunciation in order to initiate the alarm investigation phase. If the signal is not acknowledged within 15 seconds, notification signals in accordance with the building evacuation or relocation plan and remote signals shall be automatically and immediately activated. Trained personnel shall have up to 180 seconds during the alarm investigation phase to evaluate the fire condition and reset the system. If the system is not reset during the investigation phase, notification signals in accordance with the building evacuation or relocation plan and remote signals shall be automatically and immediately activated. If a second automatic fire detector selected for positive alarm sequence is actuated during the alarm investigation phase, notification signals in accordance with the building evacuation or relocation plan and remote signals shall be automatically and immediately activated. If any other initiating device is actuated, notification signals in accordance with the building evacuation or relocation plan and remote signals shall be automatically and immediately activated.* The system shall provide means for bypassing the positive alarm sequence.

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OK, thank you very much for the detailed replies. It sounds like Alarm Verification or the Positive Alarm Verification (replies 1&3) are established strategies for helping with this kind of problem. Thanks!