Was there not a chain guard ...........
I had that happen to me a few years ago too, here's the aftermath
http://i252.photobucket.com/albums/hh14/kart11/chain failure/009a_zps4532e54b.jpg
http://i252.photobucket.com/albums/hh14/kart11/chain failure/005_zpse3ce9a5d.jpg
http://i252.photobucket.com/albums/hh14/kart11/chain failure/009_zps50bf57e2.jpg
http://i252.photobucket.com/albums/hh14/kart11/chain failure/008_zps312fe949.jpg
http://i252.photobucket.com/albums/hh14/kart11/chain failure/007_zpsa889bfb4.jpg
http://i252.photobucket.com/albums/hh14/kart11/chain failure/006_zpsa8de0aa7.jpg
Mine was actually the result of my animal blowing up
ok now how can one avoid this mishap....That looks like it hurts.