This one is from Echoes FAQ list
http://www.meddle.org
On opening night at the Sports Arena, Los Angeles, California, February 7, 1980 curtains at the top of the stage caught fire when pyrotechnics were set at the start of ``In The Flesh?'' Sound engineer James Guthrie heard a crackling sound in his headphones and attempted to isolate where the sound was coming from. The sounds Guthrie heard were roadies who were attempting to extinguish the fire as Waters and Gilmour were dodging small chunks of flaming curtain falling from the top of the stage. When the fire became too much to handle Waters stopped the show at the start of ``What Shall We Do Now?''
Waters:
Hold it a minute! Whoa! Whoa! Whoa! Whoa! Whoa! Stop! Stop! Stop! Stop! Stop. Stop the film. We've decided that the best thing would be to put this fire that we have up here out. We'll scroll back to the beginning of that bit there and we'll carry on when everything's under control. Sorry but that's the best thing to do...
After a pause...
Waters:
One. Two. Wasn't that exciting? Ok, well as soon as we can [...] the house lights we'll go back to that bit in the story where the moon was out, the clouds were going across the moon. We'll go back to that bit in the story where the moon was out and the clouds were going across the moon. You remember the bit where there was a moon with clouds going across it? You remember that [...]. Ah, that's the bit okay? Thank you very much for waiting.``
Many in the crowd thought the flames were a part of the show. Considering Pink Floyd's reputation for theatricality the idea didn't seem that far-fetched.