tom wrote:
On Sat, 12 Feb 2005 06:57:57 GMT, "George E. Cawthon"
wrote:


wrote:

On Fri, 11 Feb 2005 05:06:39 GMT, "George E. Cawthon"
wrote:



wrote:


On Thu, 10 Feb 2005 05:25:23 GMT, "Bill Browning"
wrote:




They say to replace your CO alarms every 5 or 10 years. Why? If they still
test OK, why replace them?
Bill B.



imho:

I was told in my nfpa based training every 10, since a decade passing
brings new 'features' in the new products, and circuitry isn't tested
to last beyond a decade of use.

Might be a UL issue.

hth,

tom @ www.URLBee.com

That sounds almost like an old safety NCO that said a knot
in an electrical cord was bad because the electrons had to
speed around the corners and that made the wire hot.

Apparently your instructors fall into the same category. I
would be very leery of any of their personal descriptions of
how things work.

Some sensors have a limited lifetime. But many old smoke
detectors are based on a light sensor and there is no reason
that the circuit wouldn't last for decades. My original
smoke detector still works after nearly 30 years. I've got


For like 10 bucks, is it worth it? I mean if the smoke detector meant
to be replaced after 10 years(why now some come with 10 year batteries
so you just toss when the battery dies), you might be gambling with
lives.

Just say 10 bucks is cheap.



another 10 year old smoke detector (ionization type) which
is still so sensitive it goes off every time somebody make
toast.




later,

tom @ www.ChopURL.com

Who says it is meant to be replaced after 10 years? Not on


NFPA Does: http://www.chopurl.com?619




the unit. Not in the instruction manual. It is an ac wired
unit intended for long term use. Give it a test like the
instruction say and if it passes it is ok. Blindly
following some arbitrary rule for replacing the unit is not
only stupid but wasteful of resources. Test the damn thing.



Yes, but the site also says that over half of the
fires with deaths had no smoke alarms and that the
failure of the alarm to sound was most often the
result of a dead, disconnected, or missing
battery. So you are already down to less than 25
percent likelihood of failure if you have a smoke
alarm and it has a good battery.

The replacement every 10 years is based on a
rather faulty understanding of electronic failure
rate. The failure rate is nothing like a
continuous rate, but they base there
recommendation of 10 year replacement on a
continuous failure rate.

They indicated that an early test showed 1 failure
per 30 years of operation (no problem there).
They interpreted this as a 3% per year failure
rate with 30 % failure rate by 10 year. This
isn't likely because a steady failure rate is not
typical of electronic equipment. Everyone know
that electronic stuff suffers a high initial
failure rate and a low failure rate for a long or
very long period and a high failure rate near the
end of the lifetime. That's why you can buy a 30
year old radio or hi-fi and expect it to work. if
it doesn't fail in the initial year. If a smoke
alarm doesn't fail in the first month or two and
certainly the first 1-3 years, it will last long
past 10 years. Since the estimate is 1 failure
per 30 years, most failure (after initial
failures) would likely occur sometime after year
20 or year 25. And of course some would be still
operating at past year 35.