when I did resistant materials tech I was always getting hurt but never with a hammer, the ammount of times I sanded my finger tips (I did an entire project using just wood and sanders of different types; belt, disc, paper) near clean off or cut myself on a chisel or saw. Worst cut I ever got was with a hegmasaw (sp) I took it straight across my thumb. the reason for it being the worst was purely cause it ruined my project wood and set me back by 8 hours of sanding and smoothing.