Gas detectors?

Does anyone know if there are any affordable domestic detectors along the lines of "someone's turned on the gas on the cooker but forgot to check it ignited"?
I'm not overly clued up on this sort of thing but I'd imagine it'd be some sort of passive device as an electric powered gas detector sounds like a no-no - I've seen pads that change colour for co2 but not for natural/domestic gas.
Thanks in advance, Paul
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paul <at> spamcop.net

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http://www.fluesystems.com/gas_sniffer /
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BigWallop

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Paul Hutchings wrote:

If you do the calculations about the room volume, air changes per hour and the gas rate you'll find that leaving a cooker ring on but unlit is unlikely to generate explosive concentrations. [But I wouldn't tempt fate on purpose]. For burners with larger gas rates and/or where gas is likely to build up in enclosed spaces like ovens, some sort of flame failure device is included.
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Ed Sirett - Property maintainer and registered gas fitter.
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AIUI the standard way to check for a combustible mix of gasses is by using two electrically heated wires in a balanced circuit (e.g. Wheatstone Bridge) - one is exposed to the gasses under study, the other is the "control". A combustible mix on the former causes it to heat differently thus unbalancing the bridge. I doubt they could be made *very* cheaply, though undoubtedly there are other methods these days! Maplin used to sell a matched pair... oh, I see they still do. FM87 at 9.99 - may be worth a shot if you're any good with electronics; there's a basic circuit in the catalogue.
Used to have an electrically powered combustible mix detector at a place I used to work, but it was something "industrial" and rather expensive-looking.
Three alternatives spring to mind: 1: teach every member in your household what unlit gas smells like. It's a horribly pervasive smell and easily detected by most people well before it gets anywhere near a dangerous level, even with a cold. Not much good when you're all asleep, but this is what night-time routines are for. The other two suggestions are slightly less conventional :-)
2: train your dog to smell gas. Never actually heard of it being done, but there's no reason why it shouldn't be. "Hearing" and "Seeing" dogs for the deaf and the blind are capable of drawing attention to all sorts of things. In fact, it's possible that some hearing dogs are already trained to listen for unlit gas burners... I'll have to ask the sis-in-law.
3: buy canaries and keep them near potential gas sources. Arrange some kind of sensor system so that if they keel over and fall off the perch an alarm is activated.
Hwyl!
M.
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Martin Angove (it's Cornish for "Smith") - ARM/Digital SA110 RPC
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Any Chandlers or boating magazine - small 12VDC units are very popular in boats which use Propane/butane for cooking.
http://www.calormarineshop.co.uk/acatalog/Pilot_Gas_Detectors.html http://www.calormarineshop.co.uk/acatalog/SF_Detection_Gas_Detectors.html http://www.calormarineshop.co.uk/acatalog/omnitron_gas_detectors.html
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Peter Parry.
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