In June 2008, a cylinder was dropped, and its top valve hit a concrete platform.
The impact of the cylinder valve on the concrete caused the threads on the screw connection, which held the valve on the cylinder, to fail, resulting in complete separation of the valve from the cylinder.
The cylinder’s internal pressure was 600 psig.
The combination of pressure and size of the cylinder hole caused it to discharge its contents rapidly, and it flew through the air like a rocket.
Lessons Learned
Treat every cylinder as capable of becoming a projectile if dropped and the top valve sheared off,
Be aware of any compressed gas cylinders in your facility which do not have provision for protective caps, and handle them with particular care
Ensure that contractors handle cylinders safely.
Source http://www.aiche.org/CCPS/Publications/Beacon/index.aspx