Firefighters have known for years that burning small arms ammunition produces a very low level of danger to firemen. This is from the SAAMI paper, "Facts About Sporting Ammunition Fires":
Ammunition fired in the open, not enclosed in a gun's chamber, discharges with such inefficiency that the projectile will not even penetrate an ordinary fiberboard shipping container panel at very close range. When not strongly and tightly confined, smokeless propellant powders burn relatively slowly and do not explode as we know they do when fired in a gun. Pressure within a cartridge case must build up to several thousand pounds per square inch to cause the cartridge to discharge as it does in a gun. Unless it is tightly confined, as in a gun chamber, no ammunition shell case will withstand the growing pressure of gases generated by burning propellant powder without bursting before the bullet or shot is expelled with violence or velocity.Casings propelled by this type of action would likely have to impact exposed skin or eyes to have any effect. Actual injuries from such fires are so rare as to make the news, even if the injury is so minor as to normally go unreported. Thus, this news from sandiego.com:
A firefighter was struck by a casing fragment and sustained a minor injury, Rodriguez said. He was treated at the scene and released back to duty.Treated at the scene and released. This sounds like a band aid to me. Firefighters, as government employees are carefully monitored; injuries are required to be reported because of the potential for workman's compensation and potential pension effects. To be treated at the scene and released means that the injury was exceedingly minor.
©2014 by Dean Weingarten: Permission to share is granted when this notice is included.
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Update: As a wise friend reminded me, there are not enough details to let us know what really happened. I have never heard of unconfined ammunition exerting enough force to "fragment" cases; the "fragment" is not identified, and it is only an on scene report.
One Internet forum source reported that he had experience of a fragment that barely punctured the skin at a range of less than five feet from a .22 rimfire case. He concluded that any other cases were too sturdy to fragment.