[Brian Gaff]

There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Brian

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"Stewart" wrote in message
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Does anyone know if it is possible to renew the battery in the FireAngel
WST-630 smoke detector?
I have taken the battery out and thank that I could solder a replacement
in provided it was the correct size.
I am reluctant to buy a new smoke detector as they do not last any time.
Thank you.

[Robin]

Smoke detectors use Americium with a half life of over 400 years so
after 10 years there is more than 98 per cent left. The replace "after
10 years" comes from risks of failure due to insects, grease, dust,
nicotine and other assorted gunk; and electrical failure - especially
where they are never tested (let alone tested with smoke).


On 20/04/2017 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Brian



--
Robin
reply-to address is (intended to be) valid

[The Natural Philosopher[_2_]]

On 20/04/17 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Whenever you say 'I think' Brian, one cringes. Patently you don't think.

Americium half life is ~400 years.

There will be no change in sensitivity worth a damn over 10 years.


Brian



--
"Women actually are capable of being far more than the feminists will
let them."

[[email protected]]

On Thursday, 20 April 2017 09:27:23 UTC+1, The Natural Philosopher wrote:
On 20/04/17 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Whenever you say 'I think' Brian, one cringes. Patently you don't think.

He must do. He manages to get it wrong 99.9% of the time.

Americium half life is ~400 years.

There will be no change in sensitivity worth a damn over 10 years.

[John Rumm]

On 20/04/2017 09:27, The Natural Philosopher wrote:
On 20/04/17 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence
detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope
decays
the efficiency goes down, so after about 10 years its probably
whatever the
sniffing equivalent is of deaf as a post.

Whenever you say 'I think' Brian, one cringes. Patently you don't think.

Americium half life is ~400 years.

What's the "half life" on modern electronics with cheap caps, and lead
free solder?

There will be no change in sensitivity worth a damn over 10 years.

There will be no change in radioactive emissivity worth a damn over ten
years, but that is not quite the same thing.

A more common problem is the alarms becoming over sensitive as they age,
and being more likely to give a false alarm. (and hence users disabling
them)

If one were to test them (with smoke, not the test button) from time to
time and they are not giving false alarms, then its reasonable to keep
them in service longer than the recommended duration. However for many
its just going to be simpler to replace them.

There is a resonable summary of the (rather limited) research done on
this he

http://www.safelincs.co.uk/why-shoul...ter-ten-years/


--
Cheers,

John.

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[Dennis@home]

On 20/04/2017 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope decays
the efficiency goes down, so after about 10 years its probably whatever the
sniffing equivalent is of deaf as a post.

Brian


The ionisation ones and the optical ones work better with different
types of fires.
You really want both types to give the best protection from both fast
burning and smouldering fires.
You may also want a temperature rise one too.
Some detectors combine all types but i would go for separate ones to
cover faults better.

It has nothing to do with cheapness.

[Dennis@home]

On 20/04/2017 09:27, The Natural Philosopher wrote:
On 20/04/17 08:55, Brian Gaff wrote:
There seem to be two different sorts of smoke detector, most of the el
cheapo ones use a radioactive source the ionise the air and hence
detect the
presence of smoke by the change in resistance so to speak. Others use a
laser beam system.
I think the problem with the radioactive ones is that as the isotope
decays
the efficiency goes down, so after about 10 years its probably
whatever the
sniffing equivalent is of deaf as a post.

Whenever you say 'I think' Brian, one cringes. Patently you don't think.

Americium half life is ~400 years.

There will be no change in sensitivity worth a damn over 10 years.

There will be but not because of the decay.
They all become clogged with dust, etc. over time.
Best bet is to fit a ten year battery one and chuck it when flat.