Repetitive Dive

Any dive made while residual nitrogen from a previous dive is still in the body, requiring shorter limits or longer surface intervals.

A repetitive dive is any dive begun while your body still carries residual nitrogen from an earlier one, conventionally within about 6 hours on tables, or whatever your computer still shows as tissue loading. You do not start the second dive clean: your tissues are partially charged, so the no-decompression limits for the same depths are shorter than on the first dive of the day. Ignoring this is one of the classic routes to decompression sickness.

Tables handle repetitive diving through pressure groups: the first dive assigns you a letter, the surface interval improves it, and the result converts into residual nitrogen time added to your next dive. Computers do the same job continuously and invisibly, tracking theoretical tissue compartments between dives, which is why you must not share or swap computers mid-day. Two or three dives per day is routine on boats and liveaboards when the surface intervals are respected.

Practical habits for repetitive days: make the deepest dive first and plan each subsequent dive shallower, stretch surface intervals rather than compress them, stay hydrated, and keep an eye on the no-fly time your computer accumulates for the trip home. If any dive of the day pushed limits or involved a fast ascent, the conservative move is to lengthen the next interval or sit the next dive out entirely.