Worst personal injury accident? Ran the steel cutter in my Dremel across the nail on my left thumb while it was going about flank speed... It clipped the edge and buried itself under my nail... Ouchie...
Worst screw-up that could have resulted in total loss of house & home? About 35 years ago I poured some resin "water" for a Monogram Kingfisher (yeah, it was an old kit then, too) diorama and wanted it to cure a bit faster than the last pour, so I doubled the amount of hardener, and headed downstairs to eat lunch... All of a sudden I heard m' mom screech from upstairs and ran up there to find the entire upstairs completelt dark with soot, impossible to see, and made my way into room where I discovered the merry little bonfire of my dio, model, and desk on fire...
The catalyst I used too much of caused the resin to generate so much heat that it set the model, and consequently the desk, on FIRE!
Luckily, the only real damage was to my room and the hallway from soot, but it coulda been a helluva lot worse... Oh, yeah... And I was grounded from using chemicals in my room, too... Or anywhere else, for that matter...