We have a filling spec. when filling our Fire Depts airpack bottles from our cascade filling station, that limits us to a certain psi per minute fill rate. Some cascade systems also utilize a water curtain to keep the bottles cool.
It's kinda funny to think of the safety precautions taken when filling those 4500 psi bottles, sliding each into a steel cylinder that would contain it should it rupture and then closing the steel door to the chamber that houses all that. Yet we fill these 3000 psi cylinders on our guns out in the open. I'd say, determining what the manufacturers recommended psi per minute fill rate is for your guns cylinder and not exceeding that is probably good practice.
