My fifth-form teacher did something similar, only with about 5 pounds of white phosphorus. This was in the late 70s/early 80s, when the powers that be were cracking down on interesting lessons by banning all the stuff that was easy fun. For some reason he had amassed a really huge amount of WP, way more than was necessary for normal experimentation and demos in class.

He had to dispose of it, and being the sort of guy he was (quite a lot of fun, generally), he decided the best way was to go round the back of the chem block and build a small fire, then dump the WP on it and retire to a safe distance.

It worked, all right.

When the fire brigade finally turned up, the entire school campus was effectively hidden from enemy observation behind the largest cloud of white smoke you've ever seen. It could be seen for miles, and was so opaque visibility was about two feet. Took hours to dissipate.

All in all very funny, but the authorities weren't totally impressed.

pca