Yes I remember what happened to Fanny Cradocks boat.

I'm thinking he just squirted some near the sensor, as otherwise the room
is probably either blown up or incapable of sustaining life!
I forget the explosive mixture ratio now but its surprisingly low in the
flammable gas.
Brian

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"Brian Reay" wrote in message
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On 18/02/2020 12:39, Jim GM4DHJ ... wrote:
why does raw butane set off an ionising smoke detector ?

I'd be surprised (and worried) if it got near to one. Butane is denser
than air and tends to 'settle' near the floor. If there is enough in the
room that it reaches the smoke detector (which is normally mounted high
up), there is a LOT of Butane around.

I assume this is in your caravan? You should have 'vents' in the floor,
especially where there is Butane equipment (ie possible leaks). The idea
is, any Butane which has leaked 'sinks' out of the vents. That is why LPG
and Boats can be a problem- you can't have vents! Boats should have LPG
detectors but I'm not sure how they work.