Safe is a good practice, but keep in mind the amount of stored energy is ridiculous even at lower-ish pressures. A couple years ago, a friend's kid had gotten a 60 gallon horizontal from a local auction, and found an appropriate sized compressor head for it. It was working fine for a couple years...until it didn't. I'm not sure what the whole setup weighed on that (probably 500ish pounds), but when the tank failed it attempted to go into low earth orbit. The bottom is where it let go, the entire tank blew out at about 120 lbs, and the complete compressor shot up high enough to break 2 2x12 rafters. Fortunately no one was standing by it at the time. Somewhere I have pictures of the aftermath.