"All the smoke alarms went off!"
Column #863 09/10/11
On The Level
Q. .My extended family rented a 14 bedroom beach house that contained about 25 hard wired smoke alarms. At 3:00 A.M. one night the alarms went off for about 10 seconds and stopped, waking everybody up. We couldn't find evidence of smoke so we all went back to bed presuming the cause had dissipated. Twenty minutes later it happened again for 10 seconds. Still no cause was evident, so back to bed a second time. About 20 minutes later it happened a third time for 10 seconds. To find the culprit alarm we began unplugging all of them until the faulty alarm went off individually on battery backup power. We then plugged in all the alarms, except the faulty alarm. Is there an easier way to solve this dilemma?
A. Just 25 smoke alarms in a house is for me one for the record books but having them all go off at once in the middle of the night must have truly been frightening. That you were able to identify the alarm that was causing the nuisance alarm sounding was as much good luck as it was your wise approach to the problem. Iím not so sure I could be that clear headed at 3 AM with all those alarms blaring in a house full of people.
My initial guess at the cause is that it might have something to do with the salt air at the beach and I know sometimes high humidity can make a smoke alarm sound. It could also be the age of the alarm. At a conference some years ago we were given a presentation on the various aspects of smoke alarm systems and one item that was passed out was the statistic that about 3 percent of smoke alarms are bad out of the box and by the time they get to be 10 years old about 30 percent are unreliable and by age 20 they are all suspect. Thatís not to say they absolutely wont sound in the presence of smoke but just there is an ever stronger possibility that they wont. I donít know if that formula still holds after all these years but I recommend smoke alarm replacement of any alarm 10 years old or older. But 25 alarms in one house is a lot of redundancy. The minimum I have seen in a dwelling was two-- a one level, one bedroom condo.
In considering age as a potential cause I researched the requirement for interconnecting them electrically so that when one sounds they all will and I found it in one of my old code books as a new entry in the 1992 edition. 19 years ago. The beach house may be older than 19 but the smoke alarms may have been added to satisfy the code for a rental license or an insurance requirement placed on the owner who reported the use as seasonal rental.
When smoke alarmsí batteries start to get weak the alarm beeps. The beep is designed to be annoying so that youíll do something about it, preferably replace the battery. I see far too many smoke alarms taken down and the battery pulled out to shut it up and the owners will always say ďIíve been meaning to get a new battery, but just havenít got around to it yetĒ. Ask a firefighter how many times they have gone to residential fires where the smoke alarms have been disabled and they will tell you many. The truly sad ones involve a fatality. The battery replacement timed with the turning the clocks back or forward is an good idea.
The worst case at the beach house you would have had to take them all down and start putting them back one by one to find culprit. That would have taken you until dawn. Also checking the main electric panel-- and in a house of that size there might be more than one panel-- you might find the circuit or circuits the smoke alarms are on which should be dedicated circuits.
An idea for future smoke alarm design might be to build in a signal, such as a small LED light, that would go on indicating which of the many interconnected smoke alarms is the one that initiated the alarm which would remain lit until reset. That would also help identify the location of a light smoke source or some other agent responsible for setting the alarm off. Iíll bet if someone invents such an initial alarm indicator for smoke alarm systems it wouldnít take more than two code cycles before it would become code-- probably about 2018.
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