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  Reply # 1379770 4-Sep-2015 14:05
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A little plug here for the New Zealand Fire Service: They attend 3,500+ house fires every year.  In over 80% of house fires that result in a fatality, smoke alarms were not installed or not working.  If you have a smoke alarm, and it goes off, get out of the house and stay out until you are 100% sure it's not burning down...

Most detectors are either ionisation or photoelectric types.  Research from AFAC (the Australasian Fire Authorities Council, of which the New Zealand Fire Service is a member) suggests that ionisation alarms are marginally better at detecting flaming fires in close proximity to the alarm, however the Fire Service recommend photoelectric alarms as these are significantly better at detecting smoldering fires, and also flaming fires that are not close to the alarm.  Photoelectric alarms are also less prone to false alarms caused by steam and cooking fumes - things that often cause people to remove the battery from their alarm, rendering it useless.

Most smoke alarms have a life span.  Australian Standard AS 3786 states that alarms must have a service lifespan clearly indicated on the base, and that the maximum service life is 10 years, so you should replace your alarms at least every 10 years.  While in service, the alarm should be tested monthly to ensure the alarm and battery are working, and the battery changed and the alarm cleaned with a vacuum cleaner annually.  Better yet, long-life photoelectric alarms don't require a battery change - though more expensive to buy they generally pay for themselves by preventing you having to buy 9v batteries, and also remove the 3 a.m. "flat battery beep".

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  Reply # 1380154 5-Sep-2015 10:36
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When they go off for no reason I usually take them to the garage, blow all the crap out of it with the compressor and then stick them back up. Usually dust but have had spiders etc.




Richard rich.ms



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  Reply # 1380731 6-Sep-2015 18:47
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Thanks everyone, lots of interesting replies, especially the ants.

Nobody got what I was thinking of though.

There was a case here a few years back.  It resulted in a fatality and was thus well investigated and reported.

A young woman was living in a shared housing arrangement. She had her own room and there was a smoke alarm in the room.

One day, the alarm went off for no apparent reason. She removed the battery. This much is known because her housemates reported this.

That night, her laptop power brick overheated and set fire to her room. With no smoke alarm to wake her. she died.

The fire service wheeled out their usual mantra that this situation shows the importance of having working smoke alarms. They also noted that it was deeply unfortunate that the woman's smoke alarm had failed just before the fire.

The same was said at the inquest into the death and was accepted by the coroner.

I do not think for one moment that the allegedly failed smoke alarm and the fire were unconnected.

A failing power brick. Getting steadily hotter. Driving volatile components (plasticisers?) out of the plastic case. Perhaps popping a capacitor. Finally causing the pcb material to char. All that will happen long before the power brick gets to the point of igniting something it its surroundings. The smoke alarm was warning of an incipient fire.

I was reminded of that by reports of a fire last week. There were no fatalities (other than cats) so it was not well reported.

Even if our fire service does not recognize the risk, if your smoke alarm goes off, check all electronic devices for overheating.

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  Reply # 1380734 6-Sep-2015 18:55
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richms: When they go off for no reason I usually take them to the garage, blow all the crap out of it with the compressor and then stick them back up. Usually dust but have had spiders etc.


Yes, had a spider evacuate a 5 story building before, impressive for its size.

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  Reply # 1388611 16-Sep-2015 16:11
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jpoc:

A failing power brick. Getting steadily hotter. Driving volatile components (plasticisers?) out of the plastic case. Perhaps popping a capacitor. Finally causing the pcb material to char. All that will happen long before the power brick gets to the point of igniting something it its surroundings. The smoke alarm was warning of an incipient fire.



I know of a case where a uni student came home with backpack full of text books, and emptied out the books, and piled them on top a standard extension cable.

After a few days, the pressure of the books forced the wires within the insulation to meet and char, causing a  resistance char, more and more current as the plastic charred, and the extension cord got hotter and hotter and eventually caused a fairly significant, but non-fatal fire in the student's bedroom.




My thoughts are no longer my own and is probably representative of our media-controlled government


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  Reply # 1388746 16-Sep-2015 22:21
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So far, in 8 years, ours have never gone off without cause.

They run off those expensive CR123 lithium batteries - the short dumpy ones - and are wireless.

They went off once not long after installation when we were still adjusting to 19th century heating and Er Indoors threw open the door on the woodburner after it had been shut right down overnight, filling the room with smoke. Opened doors and windows and then discovered how good the monitoring was as the local brigade turned out at 7.30 am on a Sunday...!

We've had the PIR sensors on the alarm triggered by spiders, but never the smoke alarms.

Even though our house has a concrete floor, concrete block walls and steel joists in the ceiling (i.e. it is not particularly flammable!) my reaction if it goes off will be to leave the building and await professional opinion, unless I know for sure it was me burning the toast.





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  Reply # 1388756 16-Sep-2015 22:53
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They are $5-6 new with 9V battery for the cheapest ones, we replace them every 2 years because it's so little money

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  Reply # 1388818 17-Sep-2015 08:56
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loceff13: They are $5-6 new with 9V battery for the cheapest ones, we replace them every 2 years because it's so little money


Yep, I recall this point was made in another thread when I was asking for advice regarding lithium 9 volts. My point there was, yes, that's a financially sound decision, but not particularly environmentally friendly - hence why I believe longer-life batteries are a more sound way to go. This two-yearly replace and dispose method would, I think, be even more of an issue for ionisation-based alarms.

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  Reply # 1388838 17-Sep-2015 09:29
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AFAIK $5-$6 units would be ionisation types. I have asked at places like Bunnings why they stack cheap ionisation types by the cash registers while the cheap photoelectric type are further away.

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  Reply # 1388860 17-Sep-2015 09:38
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This happened to me.  I got out my torch and walked around the whole house with it, looking for and sniffing for smoke.  Checked up in the roofspace too.  Nothing.

It was the middle of Winter and we lived in quite a non-airtight house.  It was a still night,  I think what'd happened was smoke from the neighbours houses had slowly drifted under the door and set it off.

After being sure we weren't about to burn down, I took the damn thing down and replaced it that weekend (we had others in the house)

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  Reply # 1389354 17-Sep-2015 22:11
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We have a old house with a high stud and one of the first things we did is put in some of those small new long lasting smoke alarms,  and so far "touch wood" we have had no problems with them accidently going off yet.

Because we have such a high stud we would rather have a the more expensive miniature Photoelectric Smoke Alarms that dont go off when ever there is a small puff a smoke from teh fire place,  or someones burnt the toast.  Than each time the wife burns her toast I have to go out side to the garage to get the ladder to silance the smoke alarm.

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  Reply # 1389379 17-Sep-2015 23:30
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Bung: AFAIK $5-$6 units would be ionisation types. I have asked at places like Bunnings why they stack cheap ionisation types by the cash registers while the cheap photoelectric type are further away.


My guess would be that they make more money on the ionisation than the photoelectric if both are fairly low priced. Ionisation detectors are typically cheaper to manufacture, their sensonrs are much simpler than the photoelectric detectors sensors.




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