I was looking around on the physical plant website of the college I attend and I came across the specifications and standards regarding fire alarm systems (among many other things). I’m an engineering major so I have nothing better than to figure out how things work apparently. I found this statement to be fairly interesting:
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Activation of a resident room/suite smoke detector shall initiate all notification appliances within that suite only [i](usually just a sounder base and/or a strobe if in an ADA room)[/i] and shall indicate an alarm condition at the panel, annunciators and central monitoring. If the alarm is not acknowledged within 15 seconds and [b]verified[/b] within 180 seconds, then the system shall go into general alarm.
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What does verified mean in this case? The acknowledged in 15 seconds makes sense as there is 24/7 remote monitoring of all buildings on campus and can easily be acknowledged. Does this mean if the smoke or alarm hasn’t been cleared and the system hasn’t been reset within 3 minutes the general alarms will go off?
I was just wondering because the one year I was on campus someone on my floor burnt popcorn in their room and only their sounder went off. I started having a panic attack thinking we were having to evacuate the building at 11:30pm. Luckily, the problem was mitigated in a decent time besides the smell of burnt popcorn for the next 3 hours.
The feature described is actually Positive Alarm Sequence. Verified in this case means someone in a responsible position, like campus security, actually goes to the location indicated by the fire alarm system to personally investigate the situation and take appropriate action. Here is the “chapter and verse” from NFPA 72, 2007.
6.8.1.3 Positive Alarm Sequence.
6.8.1.3.1 Systems that have positive alarm features complying with 6.8.1.3 shall be permitted if approved by the authority having jurisdiction.
6.8.1.3.1.1 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.
6.8.1.3.1.2 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.
6.8.1.3.2 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.
6.8.1.3.3 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.
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.
Normally those are programmed so if only 1 smoke goes off in a suite all local alarms go off but the building alarm never activates. If any two smoke detectors go off, then the building alarm goes off.
In the code there’s a thing called “positive alarm sequence”, it’s activated when someone acknowledges the alarm within 15 seconds of it coming in. Once positive alarm sequence has been initiated, they have 180 seconds to verify the alarm and reset the panel, otherwise the building alarm will go off. If a second device goes off during the 180 seconds, the alarm automatically goes off.
Once the panel is reset, if the condition hasn’t cleared the smoke detector will go into alarm again and someone will have to start the positive alarm sequence again and reset it within the 180 seconds.
The system has to be set up for positive alarm sequence and you select which devices can be used for it (generally smokes). It’s not uncommon to find it in large event type centers though on publicly accessible pull stations, smokes, etc.
Luckily, the problem was mitigated in a decent time besides the smell of burnt popcorn for the next 3 hours.