No-Decompression Limits Table (Air)

A no-decompression limit is the longest you can stay at a given depth and still ascend directly to the surface, at a normal rate and with a safety stop, without a mandatory decompression obligation. The figures below are the PADI Recreational Dive Planner, air, no repetitive dive values. They are one agency's numbers from one decompression model, and they are printed here so you can see the shape of the curve, not so you can plan a dive from them.

What are the no-decompression limits by depth?

The table gives the published limit, the same depth in metres, the ambient pressure at that depth, and the multiplier that pressure applies to your gas consumption. The final two columns are the part most tables leave out: how long an aluminium 80 actually lasts at that depth, and which of the two limits binds first.

The Al80 duration column assumes a full aluminium 80 holding 77.4 cubic feet at 3,000 psi, a dive that ends on 500 psi, which leaves 64.5 cubic feet usable, and a respiratory minute volume of 0.6 cubic feet per minute. It also assumes the whole dive happens at the stated depth, which no real dive does. Treat it as the same kind of square profile approximation as the no-stop column, so that the two columns are being compared on equal terms.

Two things fall straight out of that comparison. First, on everything shallower than about 80 feet, gas is the binding limit and the table is nowhere near relevant. At 50 feet the printed no-stop limit is 80 minutes and the cylinder is empty at roughly 43. A diver worrying about the table on that dive is worrying about the wrong number entirely. Second, deeper than that the relationship inverts and the no-stop limit becomes the constraint, which is exactly the depth band where divers reach for nitrox.

The 140 foot row is included for completeness of the published table only. Recreational training limits stop at 130 feet, and the 8 minutes shown at 140 is not enough time to descend, do anything, and ascend, which is the arithmetic way of saying that depth has stopped being recreational diving. Working past it is planned decompression, a different activity with different equipment, gas and training, outlined in the technical diving explainer.

Why do published limits differ between agencies?

Because a no-decompression limit is a model output rather than a measurement. Decompression models divide the body into hypothetical tissue compartments, each with its own half time for taking on and releasing inert gas, and then apply rules about how supersaturated a compartment can become before bubbles are predicted to form. Choose a different number of compartments, different half times or a different supersaturation criterion, and the same profile produces a different answer.

None of the competing answers is fraudulent. They are different defensible readings of the same incomplete physiology. Buhlmann derived models with gradient factors, reduced gradient bubble models and the various proprietary agency tables all come from real work, and they disagree because the underlying science genuinely underdetermines the answer. The Buhlmann versus RGBM comparison works through what the two families actually do differently and where the practical divergence shows up on a real profile.

This is why the instruction to follow your own computer is not a legal formality. Your computer is running one model consistently across your whole day of diving, tracking your actual depth history rather than a square approximation of it. Mixing sources, taking a longer bottom time from a table and a shorter surface interval from a computer, discards the internal consistency that made either of them trustworthy.

Why does a computer usually give more time than the table?

Because a table has to assume the worst thing you might have done, and a computer knows what you actually did. A table prices your whole dive as though every minute of it happened at the deepest point you touched. Reach 100 feet for two minutes at the start of a dive and then spend the next 35 minutes at 45 feet, and the table calls that a 100 foot dive with a 20 minute ceiling, while the computer prices those two minutes at 100 feet and the rest at 45.

That extra time is real, and it is the main practical reason computers displaced tables. It is also the source of the most common misunderstanding about them. The additional minutes are credit for having dived a shallower profile, not a larger allowance to spend at depth. A diver who reads 40 minutes of no-stop time at 45 feet and then descends back to 100 will watch that number collapse in seconds.

Comfort with reading that live is a skill worth building deliberately. On a simple unit such as a Suunto Zoop Novo the remaining no-stop time sits on the main screen next to depth, which is precisely where a new diver should be looking every few minutes. On a Shearwater Peregrine the same figure is configurable alongside a graphical tissue loading display, which shows the direction the number is moving rather than only its current value. Either way, the number to watch is the one on your wrist. The dive computer roundup covers what each unit displays and how legibly.

What are the ascent rules that go with these limits?

A no-stop limit is only valid if the ascent that follows it is the one the model assumed. Three numbers define that ascent, and they are as much a part of the limit as the bottom time is.

Thirty feet per minute is slower than it sounds. It means taking a full minute to cover the distance from 60 feet to 30, which feels like hovering to anyone who has not practised it. The common failure is not a deliberate fast ascent but an unnoticed one: a slightly overinflated BCD at depth expands on the way up, the diver rises faster, the expansion accelerates, and the last 20 feet arrive very quickly. That is a buoyancy control problem wearing an ascent rate costume, and it is treated in the buoyancy and weighting guide.

The safety stop is not a decompression obligation and skipping one because you are low on gas is a legitimate call, but a dive that regularly leaves you without the gas for three minutes at 15 feet is a dive planned wrong rather than a stop you can drop. Reserve for the stop is part of what the gas planning calculator sets aside.

How does nitrox change the picture?

Nitrox lowers the fraction of nitrogen in the breathing gas, so at any given depth your tissues load nitrogen more slowly than they would on air. The way to see the size of that effect is to compute the equivalent air depth of the mix and read this table at that shallower depth instead. EAN32 at 100 feet loads nitrogen like air at about 82 feet, which moves you from the 20 minute row to a considerably more generous part of the table.

The trade is a ceiling that air does not have. EAN32 tops out at 111 feet at the 1.4 ata oxygen working limit, EAN36 at 95 feet, and going past those is a different and less forgiving kind of risk than going past a no-stop limit. The nitrox MOD chart has every mix, and it is worth reading alongside this one rather than instead of it: nitrox trades a nitrogen limit you can ascend away from for an oxygen limit you cannot.

A practical note on both. Whatever you plan, write it down before you get in the water. A folding wrist slate carrying the planned maximum depth, the planned bottom time and the turn pressure is the cheapest piece of dive planning equipment there is, and it settles the arguments that otherwise happen at depth using hand signals.

What actually causes decompression sickness within the limits?

Staying inside a no-stop limit reduces risk. It does not eliminate it, and decompression sickness after a dive that respected every published number is well documented. The model describes an average, and no diver is the average. Dehydration, fatigue, cold at the end of a dive, hard work at depth, a rapid ascent, a missed safety stop, altitude after the dive, and flying too soon all shift the odds in ways the model on your wrist never sees.

That is an argument for margin rather than an argument for despair. Ending a dive with time still on the clock, ascending slower than the maximum rate, extending the safety stop when gas allows, taking longer surface intervals and diving the deepest profile of the day first are all free. None of them require different equipment. All of them make the numbers in the table less load bearing, which is exactly where you want them.

Related charts and tools

• Air consumption by depth, the limit that usually binds first
• Gas planning calculator, for rock bottom and turn pressure
• Nitrox MOD chart, the ceiling that comes with longer no-stop times
• Buhlmann versus RGBM, why two computers disagree
• Best dive computers, the only source that supersedes this page