Thinking about it now I should have expected it . Two years ago when I collected my present van the previous owner had just refilled both gas bottles as now almost empty I went to the garage today for refilling never having had experience of doing this the very friendly girl who was serving fuel told me that they preferred to do it for me, she then connected pump etc then walked away to serve next customer while gas was being pumped into my cylinders when full she came back to disconnect there was a whoosh of gas very like a compressor blowing of I must have leapt three feet into the air as was totally not expecting any sort of noise,Have to say the lady attendant was laughing fit to burst and said it always does that. I must be getting nervous.
