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Decompression: what the no-stop limit actually means
Every dive is a decompression dive; in some you can ascend directly and in others you can't
People talk about "no-decompression dives" as if some dives existed where the body doesn't decompress. There's no such thing: the moment you start ascending, your body is decompressing. What changes is whether you can do it with a continuous ascent or whether you're required to stop along the way.
In this article you'll understand what the no-stop limit means, how tables and computers calculate it, why ascent rate is a critical parameter, and what the safety stop actually does.
It's the set of rules that separates a normal dive from a decompression accident, and the three that matter most (rate, stop, and margins) depend entirely on you.
The no-stop limit
In the article on dissolved gases you saw that the body absorbs nitrogen during the bottom phase and eliminates it during the ascent, and that the problem shows up if pressure drops faster than the gas can leave in an orderly way.
The no-decompression limit, often shortened to NDL, is the maximum time you can stay at a given depth and still ascend continuously, at a controlled rate, with no mandatory stops along the way.
That limit shrinks drastically with depth, and not linearly: at shallow depth it can be hours, while at depths near the recreational limit it's counted in just a few minutes. The reason is the usual one: higher pressure means higher nitrogen partial pressure, and so faster absorption.
Exceeding that limit doesn't turn the dive into an accident, but it changes its nature: it now requires mandatory decompression stops, with everything that implies for gas, planning, and training. Planned-decompression diving is a technical discipline with its own training, and it isn't part of standard recreational diving.
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