The rated pressure is for water, and the rating assumes the pipe is in perfect condition. And no, constant vs shock pressure doesn't make it safer. If you nick

The rated pressure is for water, and the rating assumes the pipe is in perfect condition. And no, constant vs shock pressure doesn't make it safer. If you nick it, drop it on something, etc - the rating no longer applies. Over the years numerous shops have used PVC pipe "because the compressor only goes up to 100psi and the pipe says 250", that sort of thing...and had the pipework explode and injure/kill people. ~100 psi in a PVC pipe is enough to tear through a sheet of drywall and then fatally injure someone.