This is TEPCO video  of the #4 fuel pool at Fukushima Daiichi just after midnight last night, June 14, 2011.
It is on fire by 00:46.
There is an explosion at the back of the structure which is captured in frame 1:05.
There is a flash of Cherenkov radiation  visible – at least to me – from the back of the structure between frames 1:05 – 1.07.
There is more fire and smoke at 1:31, 1:36, 1:46 and the fuel becomes energetic at 2:12. A transient criticality event  appears to have been achieved at ~1.07 although not many other people seem to see it. Fission events occur at the point of the flashes.
The fuel pool HAS disintegrated into yet another disaster. Anyone even remotely near Fukushima Daiichi with a metallic taste in their mouth should seek medical attention.