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Can smoke detectors really detect methane?

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Can smoke detectors really detect methane?

Old 7th Nov 2015, 16:08
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Can smoke detectors really detect methane?

If so, what else? From Aviation Herald;

"A Singapore Airlines Boeing 747-400 freighter, registration 9V-SFI performing flight SQ-7108 from Adelaide,SA (Australia) to Kuala Lumpur (Malaysia) with 4 crew and a cargo of 2,186 sheep, was enroute at FL320 about 400nm south of Denpasar (Indonesia) when the crew received a smoke indication in a cargo bay, descended the aircraft to FL250 and diverted to Bali Denpasar for a safe landing about 45 minutes later. Emergency services did not find any trace of fire, heat or smoke.

The smoke indication was identified to be the result of exhaust gasses and manure produced by the sheep.

The aircraft was able to depart again after about 2.5 hours on the ground in Denpasar and reached Kuala Lumpur about 2.5 hours later."

Incident: Singapore B744 near Denpasar on Oct 26th 2015, sheepish smoke indication
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Old 7th Nov 2015, 18:54
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If I recall my old cargo days correctly the book said smoke detectors may provide false warning if there's too much sheep sh!t and farts around.
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Old 7th Nov 2015, 19:28
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Extremely unlikely and a candidate for Snopes.

The methane molecules are too small to be "seen" by the detectors. A less gullible explanation would revolve around dust or fleas.
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Old 7th Nov 2015, 21:55
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With an ionization type smoke detector it's more a question of whether the emitted gases in question reduce air ionization to a similar degree as smoke does.


westhawk
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Old 7th Nov 2015, 22:42
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Are ionisation type detectors still used on aircraft? The standard cargo smoke detector just uses a beam of light and a light sensor (photo cell). An air sample is sucked through the detector and smoke increases the amount of light reaching the sensor.



It's not unknown that excess moisture in the air (due to various factors, including animal waste products) causes condensation on light emittors/sensors and causes the cargo fire test to fail. However, for a smoke alarm, two sensors need to be affected.
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Old 8th Nov 2015, 01:06
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Spraying the cargo hold with insecticide will often trigger the smoke warning.
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Old 8th Nov 2015, 02:36
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From past experience it would seem the cause is a build up in humidity. Recall an aircraft having to turn back with a similar problem in Australia.

http://www.skybrary.aero/bookshelf/books/2086.pdf
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Old 8th Nov 2015, 07:57
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Are ionisation type detectors still used on aircraft?
Ionization type detectors are flying all over the world on a variety of different aircraft types right now! But photoelectric types are much more commonly used these days, especially in more recently built airplanes. Each type of smoke detector sensor has it's advantages and disadvantages.

Boeing uses both technologies in some aircraft. However it appears from the info on Boeing's website that the 747-400F uses photoelectric sensors exclusively.

The wave of the future as far as optimal smoke detector performance is concerned appears to be with integrated multi-sensor detection systems utilizing 2, 3 or more detection technologies.
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Old 8th Nov 2015, 18:54
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Methane

You can certainly buy a light, low power consumption, methane detector if you want one.

I once had a chat with someone who designs them.
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Old 8th Nov 2015, 21:18
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Ionization type detectors are flying all over the world on a variety of different aircraft types right now!
Thanks. I remember them being in 747 Classic and 747-400 lavatories, but wasn't sure if environmental regulations had changed (with respect to radioactive materials). I see they are still fitted to 777 lavs (according to internet sources).
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