BS: CO detector - false positive?

Subject: BS: CO detector - false positive?
From: Penny S.
Date: 21 May 09 - 05:21 PM

This may be completely off the wall. After a friend's mother had a bout of CO poisoning, and I had episodes of drowsiness, the friend suggested I got a CO alarm myself. Since I don't combust anything, fully or partially, except the odd candle, I got the sort of spot detector that goes through a colour change. I put one in my car, one by my bed, one in the living room, and one on my fridge-freezer.

A little while ago, shortly before the use by expiry date, and during a spell of temperature inversion, the colour changed on the two in the living room and the kitchen, in the case of the fridge-freezer very strongly. Thinking that I had had a leak in from the neigbours below, the flue not working because of the weather, I asked them if they had a detector, which they did not, and alerted other neighbours to the possibility of leaks between properties. And opened the windows.

Today I had a visit from a fridge engineer, as the fridge wasn't working properly, and he told me that there was a leak of refrigerant - he did not tell me what it was, though I've seen the word pentane about somewhere. He said it was one which needed to be removed and sequestered as in the case of CFCs. He said pentane was the insulator. He also said the refrigerant would not affect the CO detector, which is now pale again, and a new one has shown no effect.

The time scale is about right for when the fridge went wrong. Is it possible that leaked pentane (and I'm pretty sure that the refrigerant is a flammable gas, because I remember feeling some concern when I bought the thing) could partially oxidise while hanging around in the air? I know methane oxidises in the atmosphere, but I don't know the steps it passes through on the way to CO2 and H2O.

Or could escaped refrigerant discolour a detector?

I really don't like the idea of escaped hydrocarbons round my kitchen.

Penny

Subject: RE: BS: CO detector - false positive?
From: jeddy
Date: 21 May 09 - 06:37 PM

i don't know anything about your' problem but i do know that battery powered ones don't work. we had one in our caravan and it kept going off for no reason. could the colour change have come from something as mundane as burt food or steam? sorry i couldn't help

Subject: RE: BS: CO detector - false positive?
From: JohnInKansas
Date: 22 May 09 - 06:47 AM

It may be different where you live, but in the US so far as I've heard, in all "mechanical" refrigerators intended for home use the refrigerant is a Freon® gas that is not "flammable." If your refrigerator is electric, and hums when it runs, that is most likely what you have.

The exception is for "convection cycle" refrigerators, used most commonly in recreational vehicles, running from "bottled gas," but with a very few using natural gas in homes. In RVs, the fuel is most likely propane here, but might be butane elsewhere. In these, the refrigerant is generally ammonia, which is, for all practical purposes, not flammable. Since refrigerators of this kind use a burning gas for power, a significant decrease in refrigerating efficiency could cause the burner to operate continuously, and more than normal CO would be produced.

Ammonia is also used as the refrigerant quite commonly in mechanical refrigeration units, but in most US areas is prohibited for "residential use" and is found only in "industrial strength" units, as for the freezer cases at supermarkets.

Any fluid that evaporates at normal ambient pressure and can be made liquid by compressing it can be used, at least theoretically, as a refrigerant. Early refrigerators (a half century or more ago) used a wide variety of refrigerant materials, but I haven't heard of a mechanical one using anything other than Freon (CF12 previously, now banned, and CF34, CF35 CF135, or CF125 etc in currently "legal" ones.). The only "gas" refrigerators in use here so far as I've heard are ammonia cycle ones.

If your refrigerator uses a gas for a fuel rather than having an electric motor/compressor, the constantly burning flame could have raised the CO level. The "flame" required in a home refrigerator usually is smaller than a gas burner on a cooking stove, and it is not commonly necessary to provide a separate "chimney" for venting.

"Pentane" is a hydrocarbon slightly heavier than propane or butane, and is a common component in "natural gas" - or in "liquified natural gas" (LNG) or "liquified petroleum gas" (LPG) that people use from a big tank in the back yard in lieu of a pipe to the supplier. Most people here call it "the propane tank" regardless of what gas is actually in it. Your reefer tech may have used the term "pentane" to refer generically to gas you burn, for the refrigerator or for cooking, heating, or hot water etc. Few here would use that term, but it may be fairly common usage elsewhere in the world.

The levels of CO detected by "color change" stick-ups usually are very low, so that you'll have plenty of time to notice an increase and take appropriate action. Electric/electronic devices with audible warnings can be set to trigger at somewhat higher (less sensitive) levels, since you get an immediate (and sometimes very insistent) warning and don't have to rely on someone happening by and "reading the color."

Since CO is "heavier than air" the sensors, of either kind, should be placed near floor level for maximum sensitivity/safety; but in areas where there is little air circulation too close to the floor may cause lots of seemingly "false alarms." Some CO is almost always around (if anyone is breathing), and in a "stagnant air" condition it will settle to the bottom. Manufacturer's recommendations on locations should be followed, for the device you're using. If the mfr doesn't give fairly specific instructions you should get a better kind of detector.

Some electronic CO detectors, like the Propane detectors required in US RVs, emit "test chirps" regularly, to assure you that they're working. I should be quite easy to tell the difference between these little "chirps" and the loud and insistent "warnings" if the device actually is triggered. In most cases if a good quality detector, properly installed, is giving excessive warnings, I'd be inclined to find out what's wrong with the environment rather than just blaming the detector. (A brief RTFM session to assure proper placement might also be in order?)

John

Subject: RE: BS: CO detector - false positive?
From: GUEST,Jon
Date: 22 May 09 - 06:57 AM

As far as I know, John, it depends on the age of the fridge in the UK. Newer ones do not use Freon or similar (Wikipedia suggests to me that is a CFC and we now use HCFCs whatever they are.)

Subject: RE: BS: CO detector - false positive?
From: JohnInKansas
Date: 22 May 09 - 09:48 AM

Jon,

The old Freon (there were a couple of dozen variants, with only one or two commonly used) was CFC. The newer ones generally are HCFCs, and here the Freon name is still attached, but with different numbers following.

The CFC (Chloro-Fluoro-Carbon) would be more accurately abbreviated as a ClFC but usage has been established otherwise. The HCFC, for Hydrogenated-Chloro-Fluoro-Carbon, replaces some of the Chlorine and/or Fluorine side molecules with Hydrogen, which allows the molecules to revert to "benzine ring" structures that reduce volatility and chemical activity, so that the breakdown products are less "ozone destructive." [Don't quote me to the chemists, but that's the rough idea.]

Since "Freon" is a trade name, the UK may be using a generic name (chemical name) more commonly than is done in the US, but the "Freon guys" are still about the only ones making "whatever it is that's legal" here.

There probably are still a number of old refrigerators here still running with "old Freon" in them. There was a transition period during which they could be recharged, if necessary, with the old Freon; but no new "old Freon" could be manufactured. During the transition, I've seen what used to be advertised as a "thirty dollar bottle" of CF12 for sale for $225, but it's unavailable at any price now and probably illegal to use.

I believe that currently it's illegal to recharge anything with the old stuff now. The unit has to be converted to one of the new refrigerants (usually still a Freon here).

Even "scrapping" one of the old ones requires that the old Freon be removed by a licensed person and contained for disposal. Just dumping an old 'fridge without removing the stuff, usually Freon 12 or CF12, is technically a Federal crime. (And the Federal fine for using the old Freon(s) with the wrong numbers for much of anything starts at about $10,000 per incident, the same as for barbecuing a spotted owl or for possessing an eagle feather.)

John

Subject: RE: BS: CO detector - false positive?
From: GUEST,Jon
Date: 22 May 09 - 10:11 AM

I'm pretty sure you can't "just scrap" one here either, John.

We had to replace a freezer last year. We took the pay (I don't think it was that much) to take the old one away option. Another option where I am (North Norfolk) is to pay the council to collect and dispose. I think most items, eg. microwave, washing machine, etc. are £15 but I've a feeling a fridge is more expensive.

Subject: RE: BS: CO detector - false positive?
From: GUEST,leeneia
Date: 22 May 09 - 01:45 PM

Penny, there is only one way to address this issue. Call the company which made the detectors, ask for Customer Service, and get an informed response.

I did this when my CO detector went off several times. Turned out it was caused by power outages from a cluster of thunderstorms.

Subject: RE: BS: CO detector - false positive?
From: Penny S.
Date: 27 May 09 - 06:17 AM

leenia, thanks - I'll do that.

It was not mounted near the floor, but at about 4ft 6in, so pentane, unless released close to it, (it was just round the corner from the top of the heat exchanger) should not have reached it. Pentane is written somewhere about the fridge. I can't believe they would leave a flammable gas in the insulting foam.

Whatever the gas was, it needs controlled removal, as in the case of CFCs.

No colour changes of late, anyway.

I am waiting for the new fridge. Delivery window from 7am to 2pm. I am five minutes from the shop, so got up REALLY early. But last time I had a delivery at 5 past 7, it didn't involve a removal, so of course they will come at 5 to 2. But I can't be sure. So I can't do anything....

Penny

Subject: RE: BS: CO detector - false positive?
From: Penny S.
Date: 27 May 09 - 12:24 PM

10 past 12. And then the door fell off. So I had to wait again. But, despite not having a slot till Friday, the engineer could come this afternoon, so I'm cold again.

The patch company say that refrigerant gasses could discolour the patch. Also that CO can travel as far as two floors from its source in a block of flats. Beware.

Penny

Subject: RE: BS: CO detector - false positive?
From: Q (Frank Staplin)
Date: 27 May 09 - 08:58 PM

Good article on CO detectors;
CO detection
Canadian, but applies to all in-home detectors sold in N. Am.

This thread sounds like hydrocarbon gases and CFC's are being confused with CO by some people. CFC's here have a very strong odor (added) so a leaking fridge is immediately detected.

The gas company checks for HC-leaks here (natural gas) every time the meter is checked; an Underwriters Lab CO detector is required here, as well as the usual smoke detectors.
I remember propane tanks for heating, many years ago when I was a student living in a converted garage, but haven't seen any for years, so can't give any advice.

Subject: RE: BS: CO detector - false positive?
From: GUEST,Jon
Date: 27 May 09 - 09:48 PM

Q, Gas heating in the UK is usually from the gas main and "natural gas". An alternative where this is not available is a big tank and LPG. Portable heaters may use butane (the blue cylinders over here) but I don't think the propane (orange/red) are used indoors.