FIRE ALARMS

The fire alarm people say yes. Apparently there is some radioactive material involved, that deteriorates over several years.

Fred

That would be smoke detectors .. Fire Alarms are the break-glass-pull-down thingies. John T.

Ionization smoke alarms tend to respond faster to the smoke produced by flaming fires than photoelectric smoke alarms. Photoelectric smoke alarms tend to respond faster to the smoke produced by smoldering fires than ionization smoke alarms.

Only the former have a radioactive element...

on 7/30/2020, Mercellus Bohren supposed :

Smoke detectors, or actual fire alarms? Smoke detectors have a shelf life.

John-

You got me! I have smoke detectors here, but they give off an alarm.

I wonder which Mercellus meant?

Fred

That would depend on what it actually is. Smoke detectors are supposed to be replaced at least every ten years. Some of the new ones have a lifetime battery in them now.

Gil

Whatever it is that is the basis for a 10-yr replacement period for ionization smoke detectors, it doesn't seem likely to be owing to the decay of the isotope. Am-241 has a half-life of 432.2 yrs.

has only lost 2% of initial activity. That wouldn't seem enough of a sensitivity loss to me.

I looked at a NFPA study that referenced a Dallas project that tracked new installations for a period of 10 years that claimed only 27% were still operational after that time.

However, it did not provide comprehensive data on the causes of the failures other than most were simply not replacing batteries or taken down when renters moved or otherwise destroyed. An apparent other failure mode of significance had to do with not cleaning -- I suppose if were in kitchen or the like grease buildup and all could do it, but again it didn't explain what needed cleaning or what the source of not being clean was.

But source decay wasn't listed at all and if it were the problem, none would be operational as all would decay at the same rate and have same relative source strength (presuming the initial population all of same vintage).

But easy to forget like a lot of things in life. Plus, time has a way of sneaking up on people.

trader_4 snipped-for-privacy@optonline.net wrote in news: snipped-for-privacy@googlegroups.com:

The reason for replacing the whole detecter every so many years is that most, if not all, can get dirty and become less efficient at detecting smoke and other particles over time.

Yes, you should have at least one of each kind and get new ones according to the recommended schedule.

But I wouldn 't necessarily get rid of the old ones. The one that came with my house, is AC powered and mounted to the upstairs hall ceiling, is 41 years old and still works, works well I think.

In addition to keeping it this long, I did another no-no. I opened it up and across the buzzer I put a relay that closes the circuit to a wire-pair that goes to the Fire input of my burglar alarm. So when the smoke alarm goes off it notifies the monitoring company.

This was really bad for a while when I made hamburgers in a skillet at the highest temperature and if I didn't turn off the burner when I removed the food, it set off the 18 volt siren outside my house (a couple times at 11PM) and the monitoring company called to see if there was a fire. (No fire engines yet.)

But by cooking the food two big "notches" less than the hottest, at about 80%, it no longer sets off the smoke alarm and all is good again.

Me neither.

Very interesting. Not surprised.

I meant smoke detectors, not fire alarms. I have a couple of smoke detectors and a couple of combo carbon dioxide/smoke detectors and they both started beeping. The two carbon dioxide/smoke detectors are wired together and to power on one circuit. The started beeping and I replaced the backup batteries. Turns out, both of the CO2/smoke detectors had to be replaced, after about 7 years.

On Thu, 30 Jul 2020 23:53:00 -0700 (PDT), Mercellus Bohren posted for all of us to digest...

That is correct they must be replaced according to the manufacturers specs. The sensors inside have a finite lifetime.

...

Looking at current spec sheets it seems more are related to the use of "tamper-proof" (and hence non-replaceable by design) batteries w/ a

I've still not found anything that indicates what, specifically is the failure mode of the device that would otherwise require replacement at

I did discover that apparently a lot of places have now decreed that ionization-type are not approved as standalone; only in conjunction with photoelectric type are they allowed by Code in those locales.

I suspect he meant carbon monoxide detector. These do have a finite lifetime.