I haven't got a clue, but "back of the fag packet" calculations say that the pressure difference between 500ft and 1000ft is around 0.5 inch of mercury which is 1/60th of the atmosphere.
One atmosphere is 33ft of water, 1/60th of this is around 6 inches of water. So the pressure difference on a human when you fly at 1000ft as opposed to 500 ft is less than the height of a small wave your divers have been swimming under. The lawyers may see it differently.