Question 1

What is a No-Decompression Limit (NDL)?

Accepted Answer

The No-Decompression Limit (NDL) is the maximum amount of time a diver can spend at a specific depth without requiring mandatory decompression stops during ascent. Staying within your NDL allows you to ascend directly to the surface (with a recommended safety stop) without risking decompression sickness. NDL varies by depth and gas mixture, typically ranging from a few minutes at deep depths to several hours at shallow depths.

Question 2

How does Nitrox extend NDL compared to air?

Accepted Answer

Nitrox (enriched air) extends NDL by replacing some nitrogen with additional oxygen. Since oxygen is metabolized by the body while nitrogen accumulates as bubbles, breathing a higher-oxygen mix reduces nitrogen absorption. For example, at 30 meters, EAN32 might give you 40 minutes NDL versus only 20 minutes with air—a significant improvement that allows longer bottom times or shorter surface intervals.

Question 3

What is the NDL for air at 30 meters (100 feet)?

Accepted Answer

Using standard recreational dive tables (PADI/RSDAT), the NDL for breathing air at 30 meters (100 feet) is approximately 20 minutes. After this time, you would need to perform mandatory decompression stops during your ascent to safely release accumulated nitrogen. This is one of the main reasons divers use Nitrox for longer dives at depth.

Question 4

Why do NDL times decrease as depth increases?

Accepted Answer

NDL decreases with depth because ambient pressure increases, causing nitrogen to dissolve into your body tissues faster. At 10 meters (2 bar), your body absorbs nitrogen twice as fast as at the surface (1 bar). The relationship is exponential—deeper dives require much shorter bottom times to stay within safe nitrogen limits, which is why dive computers and tables show decreasing NDL as depth increases.

Question 5

Are NDL tables accurate, or should I use a dive computer?

Accepted Answer

NDL tables provide conservative estimates based on worst-case assumptions and don't account for factors like water temperature, exertion, or individual physiology. Dive computers are generally more accurate because they continuously track your actual nitrogen absorption in real-time, often allowing slightly longer NDLs. However, tables are excellent for planning and understanding the fundamentals of dive time limits.

Identifier	MOD (PpO2 1.4)	MOD (PpO2 1.6)
Air	57 m	66 m	NDL table MOD info
EAN 22	54 m	63 m	NDL table MOD info
EAN 23	51 m	60 m	NDL table MOD info
EAN 24	48 m	57 m	NDL table MOD info
EAN 25	46 m	54 m	NDL table MOD info
EAN 26	44 m	52 m	NDL table MOD info
EAN 27	42 m	49 m	NDL table MOD info
EAN 28	40 m	47 m	NDL table MOD info
EAN 29	38 m	45 m	NDL table MOD info
EAN 30	37 m	43 m	NDL table MOD info
EAN 31	35 m	42 m	NDL table MOD info
EAN 32	34 m	40 m	NDL table MOD info
EAN 33	32 m	38 m	NDL table MOD info
EAN 34	31 m	37 m	NDL table MOD info
EAN 35	30 m	36 m	NDL table MOD info
EAN 36	29 m	34 m	NDL table MOD info
EAN 37	28 m	33 m	NDL table MOD info
EAN 38	27 m	32 m	NDL table MOD info
EAN 39	26 m	31 m	NDL table MOD info
EAN 40	25 m	30 m	NDL table MOD info

Scuba diving No-Decompression Limits (NDL) tables

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