Weber Kettle + charcoal + lighter fluid. Soak, light, then cover.
Simmer about 15-20 minutes.
Remove cover and LARGE fireball erupts.

My guess is that with the lid closed the lighter fluid vaporized, but there was insufficient oxygen for combustion ( in technical terms the atmosphere was above the upper explosive limit), which condition was corrected when the cover was lifted.

Happened at a friends house 20 years ago, and the memory is vivid.

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1982 300SD " Wotan" ..On the road as of Jan 8, 2007 with Historic Tags