I used to have fun in the 70s seeing what kind of mayhem various tubes could make. The 21FJ was most impressive if laid face-down, and a spark plug or other harder-than-glass object was thrown at it to strike it right in the middle of the bell. ka-BOOOOOOOOM! The debris field would be about 10'. The front of the tube always held together. On a 21CY or FB, the front would crack apart but not fly anywhere. If you wanted flying glass, a 7JP4 was the way to go! Those are pyrex hardeded glass, and when tossed over the fence into the cement canal, the glass shards and a cloud of sparkling phosphor would go at least 15' in the air. 21" and 27" black & white tubes did quite well too. SHHH; don't say anything but a CBS 19VP22 can make a nice crash if struck right in the middle. The metal flange holds the tube together, but the face plate shatters and sucks right through the shadow mask.
Not that any of us want to hear this report nowadays in 2005, but it was fun and nothing wasted in the 70s when this "science experiment" took place.... Ofcourse I wouldn't DREAM of doing that now, except I'd like to do it to a few of those wonderful Zenith A68ACT00X 27" tubes that left the factory with a short-to-be
Charles