How Deep Can You Scuba Dive? Limits by Certification, Gas and Narcosis

How deep can you scuba dive?

Recreational scuba stops at 40 m (130 ft). PADI calls 40 m the deepest you can go in recreational diving, on air and without decompression stops, and NAUI says its standards limit nontechnical recreational divers to the same depth. Your own limit is usually shallower, because it follows your card. After PADI or SSI Open Water it is 18 m (60 ft). Advanced Open Water raises it to 30 m (100 ft), and a deep diver specialty to 40 m.

The 40 m line is not only a sport diving convention. The US Navy Diving Manual sets 130 fsw (40 m) as the normal working limit for open-circuit scuba and 190 fsw (58 m) as the maximum working limit. It names increased air consumption at depth, nitrogen narcosis and exposure as significant limiting factors. Those factors, plus oxygen toxicity and shrinking no-stop time, are what the rest of this page puts numbers on. If narcosis is what brought you here, symptoms and onset depth are covered in our nitrogen narcosis guide.

Below 40 m you are in technical diving, with helium mixes, planned decompression and far more gas. The scuba depth record is 332 m, but that is an expedition, not a dive plan.

Depth limits by certification level

Each agency writes the depth into its own standards, and the numbers line up closely. The table gives the maximum depth for each card as the agency publishes it. PADI adds that some locations have further restrictions on depth, so a dive centre or a local rule can be stricter than your card.

Two differences are worth knowing. CMAS and BSAC start at 20 m rather than 18 m, and both tie the depth to the level of your buddy. BSAC also qualifies Sports Divers for dives that need in-water decompression stops, while PADI describes its 40 m Deep Diver limit as diving without decompression stops. BSAC also goes further on air than the other agencies in the table: its safe diving guide recommends 50 m as the maximum depth for air, and its Deeper Diver course takes Dive Leaders with decompression training to 50 m.

A card for 30 m says you have done a supervised dive there, not that you are at ease there. What the Advanced course does and does not prove is covered in is Advanced Open Water worth it.

Narcosis: the first limit you notice on air

Narcosis usually shows up well before any hard limit. DAN says it is generally felt at around 24-30 m (80-100 ft) on air or nitrox. BSAC says it becomes increasingly noticeable beyond 30 m, and Clark's 2015 review states that breathing air deeper than 30 m (4 bar absolute) will invariably cause it. The US Navy manual is the most relaxed of the four, placing the usual onset on air at about 130 fsw (40 m), very prominent at 200 fsw (61 m) and disabling deeper.

The spread matters more than any single figure. Narcosis grows with depth and differs between divers and between dives, so at 40 m on air every diver is somewhat impaired at the moment the dive needs the clearest planning. Clark puts the practical narcotic limit of air at about 90 m, then adds that at such depths oxygen toxicity would likely cause convulsions and drowning first. Oxygen, in fact, sets a much shallower floor than that.

Oxygen: why air has a hard floor at 56.6 m

Oxygen turns toxic under pressure, so every gas has a maximum operating depth (MOD). DAN describes 1.4 bar of oxygen partial pressure (ppO2) as the widely accepted limit for the working phase of a dive, and says most training organisations accept 1.6 at rest during decompression. BSAC's gas recommendations also cap ppO2 at 1.4 at the target depth. Beyond the limit the risk is central nervous system oxygen toxicity. The US Navy manual says it can occur whenever ppO2 exceeds 1.3 ata in a wet diver, and its symptoms include convulsions that the manual calls potentially life-threatening.

Air is 21% oxygen. Our nitrox calculator uses MOD = (ppO2 limit ÷ FO2 - 1) × 10, rounded down to 0.1 m. For air that gives 56.6 m at 1.4 bar and 66.1 m at 1.6 bar. The US Navy manual puts air at 1.6 ata at 218 fsw, about 66 m, so the two agree. At 40 m air is still only at 1.05 bar, so oxygen is not what stops a recreational air dive at 40 m. Narcosis, gas and decompression are.

Nitrox works the other way: more oxygen, shallower MOD. Worked example for EAN32 at a ppO2 of 1.4. Divide 1.4 by 0.32 to get 4.375, subtract 1 to get 3.375, and multiply by 10 for 33.75 m, which rounds down to 33.7 m. At 1.6 bar the same mix reaches exactly 40.0 m, so an EAN32 diver at 40 m is already at the decompression-stop limit, not the working one. You can run your own mix in our nitrox calculator.

Gas and no-stop time shrink as you go deeper

Depth multiplies every breath. Absolute pressure is depth ÷ 10 + 1 bar, so at 40 m each breath takes five times the gas it would at the surface, and PADI lists air consumption next to no-stop time as the two main limits on a deep dive. The table uses our tank duration formula for a 12 L cylinder filled to 200 bar, with 50 bar kept in reserve, and a surface air consumption (SAC) of 20 L/min. Minutes are rounded down and count only the time spent at that depth.

No-stop time falls faster than gas does. On the DECO 2000 table used in CMAS training, the no-decompression limit drops from 140 minutes at 12 m to 15 at 30 m and 9 at 39 m. In this example, from 24 m down the table ends the dive before the cylinder does. Other tables give other numbers: PADI's blog quotes 56 minutes at 18 m and 20 at 30 m. The trend is the same in all of them, and our no-decompression limits guide explains why the tables disagree.

The gas also gets harder to breathe. NAUI notes that at 40 m it is five times as dense as at the surface, which cuts maximum voluntary ventilation to about 50% of its surface value and makes carbon dioxide harder to clear. BSAC, using research by Anthony and Mitchell, treats 5.2 g/L as a recommended gas density and 6.3 g/L as the upper limit, beyond which CO2 retention becomes significantly more likely. In BSAC's table, air is at 5.1 g/L at 30 m and reaches 6.3 g/L at 40 m.

How deep do technical divers go?

Below 40 m, divers change the gas. Helium is not narcotic, and DAN says it has become standard practice to add it for dives deeper than about 45-50 m (150-165 ft), with some divers using it from 24 m (80 ft). BSAC's example mixes show how the helium share climbs with depth: trimix 23/40 for its 50 m Sports Mixed Gas course, 20/50 for 60 m and 15/65 for 80 m. BSAC recommends 100 m as the maximum depth on helium-based mixes, for divers trained and qualified to use them.

These dives come with planned decompression, several cylinders and much more gas planning. PADI says its technical dives are typically longer than recreational ones, can be deeper than 40 m (130 ft), and use special equipment, dive planning procedures and specialised gas mixtures. How helium changes narcosis, and how a mix is chosen for a target depth, is covered in why divers use helium in trimix.

How deep can a human dive on scuba? The record

The Guinness World Records mark for the deepest scuba dive in sea water is 332.35 m (1,090 ft 4.5 in). Ahmed Gabr of Egypt set it in the Red Sea off Dahab on 18 September 2014. Guinness reports that he reached the depth in about 12 minutes and needed nearly 15 hours to get back to the surface. The previous record, 318.25 m, was set by Nuno Gomes in 2005, also off Dahab.

The record has been questioned. In the summer of 2020 Guinness received anonymous claims about irregularities in the gas, the instruments, the rope angle used to calculate the depth and the depth tags. After its review Guinness said it was satisfied that Gabr reached 332.35 m and continues to recognise him as the record holder. Either way, a dive like this tells you what one prepared team achieved once, not what scuba can routinely do.

Planning a dive near your depth limit

Your card sets the maximum. The depth you actually dive should come from the plan for that day, and the agency standards suggest a few habits:

• Agree the maximum depth before you get in, and turn the dive there. PADI reminds divers that local rules can be stricter than the card.
• Add depth in steps. BSAC's Sports Diver course works down to 40 m in 5 m increments, and CMAS asks Two Star divers for three extra dives at 30-40 m before diving to 40 m.
• Check the no-stop limit for the depth you reach, not the depth you planned. On DECO 2000, going from 30 m to 33 m cuts it from 15 to 12 minutes.
• On nitrox, analyse every cylinder and know its MOD. The US Navy manual requires the mix in each scuba bottle to be analysed before every dive.
• Plan reserve gas for the deepest point. A problem at 40 m uses gas five times as fast as the same problem at the surface.