Deep dive

In recreational terms, a dive beyond 18 m, down to the 40 m limit; deeper water means narcosis, short no-deco times, and fast gas consumption.

In recreational diving, a deep dive is generally any dive beyond 18 m (60 ft), extending to the recreational limit of 40 m (130 ft). Depth is where the physics bites: at 30 m the ambient pressure is 4 atmospheres, gas is consumed four times faster than at the surface, colors wash out to blue-gray, and nitrogen narcosis begins to blunt judgment for many divers, sometimes noticeably by 30 m.

The dominant constraint is the no-decompression limit, which shrinks fast with depth: roughly 20 minutes at 30 m and under 10 minutes at 40 m on typical computer settings, compared with around an hour at 18 m. Deep dives therefore run as a short, planned bounce to the deepest point first, then a progressive ascent, with careful gas planning, a controlled ascent rate of 9 to 18 m per minute depending on agency, and a 3 minute safety stop at 5 m.

Training matters: the deep portion of the Advanced Open Water course introduces 30 m, and the Deep specialty extends to 40 m with narcosis checks and gas math. Beyond 40 m is technical diving territory with decompression and different gases, not a place to drift into on air. Plan gas with rock-bottom reserves and treat any narcosis symptoms as a cue to ascend a few meters.