I'll come back to you on this! Much of what PADI recommends tends to be out of date, so I'm more concerned to find what DAN's current recommendations are. I'm damned if I can find them on either the Americas website or the Europe one. Lots of references to it, no actual print. I certainly don't remember 1000ft, though I'm not going to say more until I can find definitive information.

In any case, the rule (per DAN) is not 18 hours. It's 12 hours for moderate diving and 24+ hours for deco diving. I thought it used to say 18 hours for non-deco repetitive diving, but I haven't been able to find that either.

Other readers of this semi-private discussion (I won't call it dispute - Elbert and I know each other too well for that - should note that whatever the numbers are, it's a grey scale and not black and white. It's not safe to go to 999ft and dangerous to go to 1001ft. A lot depends on the individual - his (her) fitness, general health, state of hydration (the biggest single factor in all of this), and history. If you're accustomed say to flying to 2000ft after diving and have never had a problem, well it's probably OK for you. It doesn't suddenly become dangerous because DAN or PADI or anyone else brings down the maximum recommended altitude. Equally, if you're a novice looking for guidance it pays to listen to what people say and then be conservative, in this and in all matters diving.