We've had two in our agency (70 officers) in the last 15 years.
(1) A new officer who got the field strip sequence wrong and "cleared" the chamber with a loaded magazine in place before dry firing, almost shot a fellow officer.
(2) A Captain, nice guy but a klutz, who "holstered" his weapon in his hip pocket with his finger on the trigger, shot himself in the calf.
It can be successfully argued that (1) wouldn't have happened with a gun that you didn't have to dry fire to take down and (2) wouldn't have happened if the gun had a long heavy D/A or engaged manual safety.
Be that as it may, the Glock, like any tool, is only as safe as the user and bad things happen if you don't handle it properly.