To my knowledge Sankey kegs do not not have PRV.That is true that Sanke couplers have a PRV, but we pressurise through the coupler. The guy who died with the plastic keg was using it on a sanke stand, which was set at a pressure that a sanke could take.
It is the keg dispensing coupler that has it.
The keg couplers used for filling and cleaning do not have PRV.
14.9 Psi in pressure vessel is still a lot of pressure.
I tell you this from my own experience.
I was cleaning 15 BBL bright tank.
I was depressurizing it from bottom port.
When tank had about 1-2 psi pressure (by pressure gauge) I decided to open a 4" top port.
Lucky me that my head was not over the port because 4" end cap shot up like a bullet.
It is not a lot of fun when there is 4" piece of metal flying around you.
Needless to say I make sure that there is no pressure before I open any pressure vessel now.
A little pressure over a large area equals a big force.