Apparently.. the "professionals" either aren't so professional or just plain careless.
http://www.kpho.com/education/16341159/detail.html
NEW BEDFORD, Mass. -- A firearms instructor in southern Massachusetts has been assigned to other duties after his gun accidentally went off while he was teaching a class on weapons safety.
Officials said the Glock handgun discharged while Maj. Donald Lamar was demonstrating to Bristol County deputy sheriffs how to safely holster the weapon. The bullet ripped a hole in Lamar's pants but missed his leg and foot. Sheriff Thomas Hodgson said the officer made a "gross error in judgment" by not emptying the weapon before the class last week.
Lamar, a certified firearms instructor since 2005, was transferred to another division and will not carry a firearm while the incident is being investigated.