I heard several loud explosions over a period of 10-15 minutes or so. I have never heard a petrol station or gas cylinder explode so I am guessing it is that? Does the initial explosion have several repeating explosions? I had a search and couldn't find an answer that fitted exactly. I have recorded it and put on youtube but if there is a simple explanation, no point linking it (plus then I can delete it so I don't look as nub as I am). Cheers.