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Author Topic: Should you replace photoelectric smoke alarms every so many years?  (Read 4730 times)

TelephoneDude85

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Should you replace photoelectric smoke alarms every so many years?
« on: September 24, 2015, 09:51:59 PM »
I have a Vista 20P system, and recently picked up some new in box System Sensor photoelectric smoke/heat alarms and have 1 hooked to the system now. Do these need to be replaced every so many years like the stand alone smoke alarms do?

I know with the ionization alarms, they should be replaced every 10 years, but that's because the Americium 241 has a short half life and is no longer strong enough to reliably detect smoke. Photoelectric on the other hand is an LED and a sensor, plus some circuitry to make it work, so I can't see it needing replacement unless something failed with it, which would set a trouble code in the panel.

I'm thinking of replacing the various smoke alarms in the house with the System Sensor ones and having it tied into the panel. We did have hardwired ones installed when the electricians upgraded the service, but all of those failed within a year, so I went back to standalone ones.

Just wanted to make sure these System Sensor alarms are still useable, as they are older units, but still never used.

Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #1 on: September 24, 2015, 10:33:34 PM »
Every 10 years for any kind of smoke detector is a general rule... Most of them will have a date on them.

Your reasoning about the half life of Americium is wrong however:
Americium-241, with a half-life of 432 years, was the first americium isotope to be isolated.....

I think it's more as a safety thing in case something fails silently...

TelephoneDude85

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #2 on: September 25, 2015, 12:41:50 AM »
Thanks for the info. The half life thing came from a friend that is a science geek, and it kind of made sense. I thought the half life was around 400-500 years, couldn't remember. (Did a science project on Americium back in Jr High)

So 10 years from that date, or from install? really don't see what could go wrong on one that's been stored, but I'm not for sure either, that's why I'm asking on here.

I've also seen photoelectric detectors that were part of an alarm system that looked pretty old, yellowed plastics etc. and they were on systems that had routine maintenance done by alarm techs. (my work has some like that) Shouldn't it throw a trouble code if the detector goes belly up?

AlarmMike

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #3 on: September 25, 2015, 02:04:14 AM »
NFPA advises to replace ALL smoke detectors 10 years from date of manufacture.
To the world you may be one person, but to one person you are the world.
- Kidney transplant recipient 04/27/2011

Update_My_Alarm

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #4 on: September 25, 2015, 02:28:22 AM »
As Guyfromhe and AlarmMike posted, general rule is about 10 years from manufacture.  Same goes with CO detectors, but 6 years for those on the safer side.

The issue with photoelectric detectors is that the smoke detection chamber (particle chamber) collects particulates like dust over time.  This eventually reduces the sensitivity of the sensor and thus, renders the detector useless and should be replaced.  More intelligent detectors like 2WTA-B from System Sensor automatically adjusts sensor gain to combat the deteriorating conditions of the sensing chambers and once it passes some gain threshold actually signals a clean-me or maintenance signal to a controller.  You can even clean out the sensing chambers and reset the gains too without chucking out the whole detector.

The above is what I've been told anyway.  :-)

TelephoneDude85

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #5 on: September 25, 2015, 10:44:45 AM »
Ok, duly noted. I will take that advice. I can definitely see replacing CO detectors, as they seem to use a chemical reaction, and I'm guessing after awhile those chemicals could deteriorate and become less effective. I think the photoelectrics have the "clean me" feature, and the chambers are easily opened to do just that. Mine are in fact @WTA-B, but they do not have a date stamped like every other detector I've seen, unless it's an obscure format.


Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #6 on: September 25, 2015, 10:58:30 AM »
Depending on the sensor and the system it's working with you may or may not get a notice when something is wrong..

I think the default state of a PE detector is no light so if the LED dies it would never know.  Also components have a manufacturers rated useful life (MTBF - Mean Time Between Failure). This doesn't mean it will go bad after that period it means it's at a higher risk of it and the detector may or may not notice a component fault.

Being as these are life safety devices everyone errs on the side of caution vs. chance.

You will be long dead before the material can't ionize any more, that is not the failure method of most smoke alarms.

Like I said usually there is an expiry or manufacture date on a sticker or stamped into the plastic somewhere on the unit.   If it's an expiry that's when it's "done" of it's a manufacture then 10 years from that date it's probably even mentioned in the manual.  Even if you do it at 10 years from the install date you will _probably_ be fine but you are wading into murky waters again....


Just because something is recommended doesn't mean everyone will follow it...
People drive without licenses does that mean they will get into an accident for sure? NO
People don't have smoke alarms does that mean they will definitely die in a fire? NO
People use the same smoke detector for 30 years does that mean it's not working for sure? NO

If your not going to replace them you should at least be testing them very regularly (and properly with canned smoke, not by pressing the button) You should also be cleaning the chambers in the PE ones yearly/bi yearly per the instructions.

Some will throw errors (for SPECIFIC failure modes) some will not give any indication.  Other failure modes will go undetected.
10 years can yellow a case pretty bad depending on the environment... I would expect them to be following code pretty closely as they could get a big fine if the local AHJ inspects and finds them non complainant.


murphy62

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #7 on: September 25, 2015, 11:55:27 AM »
The default state of a PE detector can't be no light.  The light beam has to be there so the smoke can interrupt it.  A battery powered one may be pulsing the light at some interval, to prolong battery life, but the light has to be on to detect smoke.

Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #8 on: September 25, 2015, 12:09:15 PM »
I could be wrong about this (and I think I stated it in a poor way) but as far as I understand:

The LED is always ON but it's essentially hitting a wall (corner) and the detector sees no light when there is no smoke.

When smoke enters the chamber it refracts the LED light and causes it to bounce around the corner and into the detector, the smoke doesn't block the light or it wouldn't go off until it got ridiculously smoky.

Per this article: http://home.howstuffworks.com/home-improvement/household-safety/fire/smoke1.htm

So when I said the default state was no light I meant at the detector, not at the LED...

TelephoneDude85

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #9 on: September 25, 2015, 03:51:22 PM »
Really great info guys. I agree being that they are life safety, that you should go by industry/mfr. recomendations, regardless if it's in your own home or a customer's premises.

I've heard about the canned smoke thing too, as some older ones, it only tests the horn when you push the button, not the actual detection circuitry. (wasn't there a new requirement that required the test button to test the detection portion?)

This article says there are 2 kinds, ones that the smoke scatters the light beam and causes a sensor to "see" it, and one where the smoke blocks the beam and disrupts it. If you were monitoring the sensor closely, even light smoke would decrease the beam by a small amount, right? http://www.enggcyclopedia.com/2011/11/photoelectric-smoke-detectors-work/

Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #10 on: September 25, 2015, 04:07:16 PM »
On your own home you get to be concerned for your own/family's life and if it's a customer you have to be worried about litigation for screwing it up.

Some of them will trip the detection circuit some just test the buzzer, none of them actually test if it can actually see/detect smoke.... Canned smoke will test the detection capabilities, the circuitry and the buzzer at the same time and a $9 can will last you years.

I always do a full system test (burglary and fire) including comms once a year with canned smoke at each of my monitored and unmonitored detectors, sometimes twice a year.

I'm sure all kinda of designs exist but the ones I have opened to clean have all had the sensor around the corner from the source...

TelephoneDude85

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #11 on: September 25, 2015, 04:29:33 PM »
On your own home you get to be concerned for your own/family's life and if it's a customer you have to be worried about litigation for screwing it up.

Some of them will trip the detection circuit some just test the buzzer, none of them actually test if it can actually see/detect smoke.... Canned smoke will test the detection capabilities, the circuitry and the buzzer at the same time and a $9 can will last you years.

I always do a full system test (burglary and fire) including comms once a year with canned smoke at each of my monitored and unmonitored detectors, sometimes twice a year.

I'm sure all kinda of designs exist but the ones I have opened to clean have all had the sensor around the corner from the source...

Yes, when people's safety is involved, cutting corners is not an option. As for the canned smoke, I've seen it at a firefighting supply house, so I may just get some from them, that way I KNOW my system(s) are working. I think the detectors I have are the around the corner beam too, but I have seen pics of some that span a ceiling, a transmitter at one end, and a receiver at the other, don't know if those are still common, it was in a firefighting book from early 2000's

Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #12 on: September 25, 2015, 05:56:16 PM »
I got mine at a local fire safety shop... It's super expensive here (I think I paid $25 for it) and you will pay a small premium buying it in a retail store.  All the ones I found online the shipping made it just as expensive as getting it locally. If your in the USA you can often get it shipped for free.

I use the "Smoke Check" brand with the small red cap, works on all my PE and ionizing detectors just fine.

I've never seen an open air detector like that but it wouldn't surprise me if they are around somewhere.


AlarmMike

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #13 on: September 25, 2015, 09:37:04 PM »
Note regarding canned smoke...

Make sure you follow the detector manufacturer's recommendations regarding testing the sensor, especially regarding the use of canned smoke.  Canned smoke MAY leave behind a residue, diminishing the sensitivity.  Often times there is a prescribed distance from which to spray the "smoke".
To the world you may be one person, but to one person you are the world.
- Kidney transplant recipient 04/27/2011

Guyfromhe

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Re: Should you replace photoelectric smoke alarms every so many years?
« Reply #14 on: September 26, 2015, 02:06:09 AM »
I thought the whole idea behind using canned smoke was to avoid residue build up on the sensor...

The can has directions about distance from the detector to spray from and length of spray, I don't recall seeing anything in my detector manual about it, I would imagine it would depend on the formula of the "smoke"...

I've been following the directions on the can and cleaning the sensors regularly anyway and I haven't noticed any issues.

 

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