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Smoke detectors

Rat

Not bored. Never bored.,
Rat
Joined
May 19, 2003
Messages
10,629
Location
Leicester, UK
At my parents' house, there was a smoke detector in the living room. If you burnt toast or bacon in the kitchen (two rooms away), the alarm would go off. And quite rightly, too. In the last house I lived in, there was one in the living room (one room from the kitchen) that went off every time you cooked anything. After that, I decided I'd rather be one of those people that died because their smoke alarm had no batteries, rather than cancelling it several times a day.

However, as any smoker can attest, tobacco smoke does not appear to set them off. Or dope, for that matter. In my parents', every Friday and Saturday night, after the folks had gone to bed, I'd have several mates round. Everybody would smoke, there'd be dope going round in massive quantities, and we'd even be doing buckets on occasion. But never once did this set off the smoke alarm, even when the air was visibly thick with smoke.

My first thought was fat/oil smoke, but the toast did away with that theory. Obviously, also, fags, dope, toast, and bacon are all organic materials. If you go on a train in this country now, an announcement informs you that smoking is forbidden, and that this includes the end-of-carriage vestibules, and the toilets, which include smoke detectors. Is this just a scare tactic?

So, is this just a matter of volume (unlikely, considering), or are there different types of smoke that set off alarms? And is the train thing just a scare tactic, or do the trains have a different type of smoke alarm, which can detect tobacco smoke?

Cheers,
Rat.
 
Thanks for the speedy reply. That answers my second question. So, how the difference in the detection between dope and toast. My, how well the two go together....

Cheers,
Rat.
 
Hmmmmmmm.

The first question is a good one. My first guess would be that the level of smoke goes up gradually with cigs(fags..whatever) and that the level of smoke goes up much faster when you burn toast. The smoke detectors work by detecting the interference of the smoke with the emissions of a radioactive isotope. (Unless something new comes around, like the link above.) I'm thinking a gradual increase might 'fool' the detector.


But I could be full of $h!t, too.
 
hmmmm.... when my grandparents were alive they did tend to set of the smoke alarms in my dad's house. That was perhaps because it was clear BEFORE they arrived... and they were human smokestacks.

When my grandfather died my aunt (dad's sister), my grandmother and a couple of my late uncle's grown children (my uncle was the youngest of the siblings and died first from cancer) stayed with my dad. My dad temporarily disconnected the smoke alarms... and spent most of the duration of their visit sitting on the porch outside because he was the only of the the group who did not smoke (well, him and my step-mother who spent many years learning to quit).

My dad quit smoking cigars in the mid-1960's when his dentist found the beginnings of mouth cancer. My grandmother quit smoking a couple years after my grandfather died... her new boyfriend did not like the smell of cigarettes.
 
"...and we'd even be doing buckets on occasion. "- Rat.

Bearing in mind the ever present threat of nannywatch software to the JREF mission, could you possibly explain the above remark?

Exactly what were you doing with (in?) the buckets?
Were they plastic or zinc?
Did they suffer corrosion afterwards?
Were there many casualties?

On topic- I find grilling bacon is the easiest way to set off detectors. Whether this also applies to aircraft toilets is beyond the scope of my current research.
 
Besides the IR detectors (those were smoking, not smoke, detectors) in the other post, there are two main domestic types used: Ionisation (using a radioactive source and high voltage in a chamber) and photoelectric (using an emitter/detector pair detecting light scattering or obstruction). The ion type detect more of invisible combustion products, while the PE type detect visible particulates of smoke. All can be designed with different sensitivities and time constants (for self-zeroing and background canceling) according to application needs.

Dave
 
In my experience ionisation detectors are over sensitive to cooking fumes. I fitted an optical detector which has virtually eliminated false alarms from cooking.
(I say vitually because my son tells me he managed to set it off when I was on holiday)

I can't remember which way it is, but I think ionisation detectors respond better to smouldering fires, and optical to faster growing fires.

Dave
 
Smoke detectors have some Americum inside.

This is (AFAIK) the only man made, and the only transuranic element that you can buy in Walmarts or Woolworths.
 
But keep science in perspective. It is doubtful that dope will be smokinng itself when you go to sleep. Buuuuut...it's conceivable you could decide to do a load of clothes drying upon retiring. And one night my 2 detectors went off when my dryer caught on fire (smoke) One detector was right outside the laundry area and the other was in my bedroom. I sat right up in bed, upon hearing the alarms, and knew right away, from the smell, what had happened. At first I was gripped by fear, like, "Where's the fire?" I ran to the laundry room only to find nothing there but smoke and smell, thank goodness. The next day I took the dryer apart. The idiot. They put the element way near the bottom of the dryer where the lint can collect!
 
Stayed in a holiday cottage once. Smoke detector on kitchen ceiling. Middle of the night , awakened by beeping. LED on detector flashing.
Checked for smoke, fire, impact craters. Nothing. Beeping had stopped.
Back to bed. Twenty minutes later. Same story.
Disgruntled, removed detector and read teeny print...Americium source...blah, blah.. removed battery. Back to bed.

Twenty minutes later, beep...beep.

Out of bed, seething, open back door, stuff detector in coal shed, wondering in a vague, 2am way about the power output of a radioactive source which could drive a beeper even with no battery... must be a capacitor in there... back to bed. Cold shouldered by seriously annoyed Her Ladyship.

Twenty minutes later...

It was the low battery warning in her cellphone.
 
Soapy Sam said:
Stayed in a holiday cottage once. Smoke detector on kitchen ceiling. Middle of the night , awakened by beeping. LED on detector flashing.
Checked for smoke, fire, impact craters. Nothing. Beeping had stopped.
Back to bed. Twenty minutes later. Same story.
Disgruntled, removed detector and read teeny print...Americium source...blah, blah.. removed battery. Back to bed.

Twenty minutes later, beep...beep.

Out of bed, seething, open back door, stuff detector in coal shed, wondering in a vague, 2am way about the power output of a radioactive source which could drive a beeper even with no battery... must be a capacitor in there... back to bed. Cold shouldered by seriously annoyed Her Ladyship.

Twenty minutes later...

It was the low battery warning in her cellphone.
Click to expand...

Pretty good!

But I was kind of waiting for the punchline to be that "...Chucky showed up". :D
 
Dave_46 said:
In my experience ionisation detectors are over sensitive to cooking fumes. I fitted an optical detector which has virtually eliminated false alarms from cooking.
(I say vitually because my son tells me he managed to set it off when I was on holiday)

I can't remember which way it is, but I think ionisation detectors respond better to smouldering fires, and optical to faster growing fires.

Dave
Click to expand...

Actually, it is the other way about. Ionisation detectors are notoriously unreliable when it comes to detecting smoldering fires, failing to go off about 85% of the time.

A couple of sites with a strong point to make are these:

http://www.joinourcrusade.com/index.php
http://www.firecrusade.com/index.htm
 
Why does my alarm go off when I boil pasta? My pans are as clean as I can make them!
 
TheBoyPaj said:
Why does my alarm go off when I boil pasta? My pans are as clean as I can make them!
Click to expand...
You remembering to put the water in the pan?

Cheers,
Rat.
 
The Whether Man said:
Actually, it is the other way about. Ionisation detectors are notoriously unreliable when it comes to detecting smoldering fires, failing to go off about 85% of the time.

A couple of sites with a strong point to make are these:

http://www.joinourcrusade.com/index.php
http://www.firecrusade.com/index.htm
Click to expand...

Yes, you are correct, grovel grovel. That will teach me to check first. In defence, I did use weasel words "I can't remember which way it is...". but I got it wrong.

I looked at the websites, and he seems to have a bit of an issue with someone, doesn't he.

I don't know the procedure for writing standards in the US, but in the UK all interested parties are involved in the drafting committee (in theory), so the standard should be OK (more or less).

When there is a standard test for a product, then the product will always be designed to pass the test. The trick is to get the test right. The opinion on those websites seems to be that they didn't.

Also, ionisation detectors are cheaper than optical, so it seems inevitable that they will be used more often than perhaps they should.

Dave
 
TheBoyPaj said:
Why does my alarm go off when I boil pasta? My pans are as clean as I can make them!
Click to expand...

Its probably something technical like the particle size of the water droplets causing it to alarm, but I don't know for certain.

Yesterday evening the leader of the opposition (Mrs Dave) was cooking some gammon, and the ionisation detector about 12m away through two doorways went off, while the optical detctor about 3m away in the same room didn't. I think I did right in changing that one to optical.

Dave
 
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