Scuba No-Decompression Limit Table

What a No-Decompression Limit Is

Every breath you take underwater loads nitrogen into your tissues. The deeper you go, the higher the pressure, and the faster nitrogen dissolves into your blood and tissues — this is Henry's law doing its quiet work. As long as you ascend slowly enough, that nitrogen off-gasses harmlessly through your lungs. But stay too long at depth and your tissues absorb more nitrogen than a direct ascent can safely release. At that point you would need decompression stops — mandatory pauses on the way up — to avoid decompression sickness.

The no-decompression limit (NDL) is the maximum time you can spend at a given depth and still ascend directly to the surface (with a normal ascent rate and safety stop) without required deco stops. It is the single most important number in recreational dive planning, and it shrinks fast as depth increases: 55 minutes at 60 feet becomes just 10 minutes at 130 feet. Memorize the shape of that curve before you memorize any number.

Important framing: this page is a simplified recreational reference. Real dive planning uses your training agency's full tables or a dive computer, accounts for repetitive dives and surface intervals precisely, and is taught — not read. Nothing here replaces certification.

The Reference Table

Two patterns to internalize. First, the limit roughly halves every 20–25 feet past 60 feet — depth is brutally non-linear. Second, below about 60 feet your air supply usually ends the dive before the NDL does; above 80 feet the NDL increasingly becomes the binding constraint. Good divers plan around whichever comes first.

Why Limits Shrink With Depth

At the surface your body is saturated with nitrogen at 1 atmosphere. At 33 feet the pressure doubles to 2 atmospheres, and nitrogen loads roughly twice as fast; at 99 feet it is 4 atmospheres. Different tissues absorb at different rates — blood fast, fat and joints slowly — which is why the full tables track multiple "compartments." The simplified table above bakes all of that into one conservative number per depth. You do not need the physiology to dive safely; you need to respect what it implies: depth is the dominant variable, and small depth increases cost large time decreases.

Surface Intervals in Plain English

Between dives, your body off-gasses nitrogen — but slowly. A surface interval is the rest on the boat or beach between dives, and it directly buys back bottom time on the next dive. The practical rules:

• Minimum 60 minutes between recreational dives is the common guidance; longer is always more conservative.
• A short interval after a deep dive leaves significant residual nitrogen — your second dive's limit is shorter than the table says. This is exactly what full tables and computers calculate.
• Plan the deepest dive first. Going deep after shallow ("reverse profiles") is discouraged because the models handle it poorly.
• Hydrate, stay warm, and avoid alcohol between dives — dehydration and cold are believed to increase decompression stress.
• No flying after diving: 12 hours minimum after a single dive, 18+ after multiple days — the cabin's lower pressure is an unplanned ascent.

Air Consumption Basics

Your SAC rate (surface air consumption, in cubic feet or litres per minute) measures how fast you personally breathe down a tank. New divers often run 0.8–1.0 cu ft/min; experienced relaxed divers reach 0.5–0.6. Depth multiplies consumption: at 66 feet (3 atmospheres) you burn air three times faster than at the surface. The estimator above combines tank size, SAC, and depth — and the lesson it teaches is consistent: plan the dive on air, treat the NDL as the ceiling. The standard gas rules: turn the dive at a pre-agreed pressure, keep a reserve (the classic "rule of thirds" for overhead environments; recreational divers keep a healthy margin above empty), and never let eagerness override the gauge.

SAC improves with exactly the things training teaches: slow deep breathing, good buoyancy (kicking less), staying warm, and staying calm. Chasing a low SAC number is less important than watching the gauge honestly.

Ascend Like It Matters — Because It Does

Most decompression risk is managed in the last 30 feet. Ascend no faster than 30 feet per minute (slower is better), and make a 3-minute safety stop at 15–20 feet on every dive — it is called "safety" not "optional." Watch your computer or gauge, not your buddy's bubbles, for the rate. The final ascent from the safety stop to the surface should be the slowest part of the whole dive. Rapid ascents are the classic trigger for lung overexpansion injuries and decompression sickness alike, and nearly all of them start with "I was just going up to look at something."

The Buddy System, Done Properly

A buddy is not a photo subject — it is a redundant safety system. The pre-dive check (BWRAF: BCD, Weights, Releases, Air, Final check) catches the misrouted inflator hose and the forgotten weight belt that become emergencies at 60 feet. Agree before entry: maximum depth, turn pressure, who leads, and the lost-buddy protocol (search for one minute, then surface — the missing diver does the same, which is why it works). Stay close enough to share air without chasing: an arm's length in low visibility, a few kicks in clear water. And the deepest rule of buddy diving: any diver can call any dive for any reason, no justification required, no judgment permitted.

Dive Conservative: Computers, Tables and Judgment

Modern divers plan with computers that track nitrogen continuously — including multilevel profiles, where time at varying depths is credited precisely. Tables assume a square profile (all time at maximum depth), which is more conservative. Whichever you use, add personal conservatism: dive the shallower of what the table and your comfort allow, add safety stops even when not required, and treat the NDL as a limit the way you treat a speed limit — legal at the number, safer below it. Cold, exertion, dehydration, and multi-day repetitive diving all argue for extra margin. The ocean rewards the cautious with decades of diving; it collects the bold as statistics.

What This Tool Is NOT

To be explicit, because the stakes deserve it:

• Not training. Safe diving requires in-person instruction, confined-water practice, and supervised open-water dives through a recognized agency (PADI, SSI, NAUI, BSAC and others).
• Not a substitute for a dive computer or official tables. This is a simplified single-dive reference; it does not compute repetitive groups, residual nitrogen, or multilevel credit.
• Not medical advice. Diving with asthma, heart conditions, ear problems, or while pregnant requires a dive-medicine physician's clearance — not an internet article.
• Not permission. If any part of a planned dive feels wrong — conditions, equipment, your own body — the correct action is to sit it out. The sea will be there tomorrow.

Common Mistakes New Divers Make

• Chasing depth. The best reef life is at 30–60 feet, where light, colour, and bottom time are all richest. Depth is not achievement.
• Ignoring the gauge. Check air, depth, and time on a fixed rhythm — every few minutes, not when something feels wrong.
• Skipping the safety stop because "the table said I had time." The stop is cheap insurance on every dive.
• Holding breath on ascent. Never hold your breath while ascending — expanding air must escape. Breathe continuously, always.
• Diving with a cold or congestion. If you cannot equalize easily at the surface, you cannot equalize at 30 feet. Descending congested risks burst eardrums.
• Trusting memory over instruments. "I think we have plenty of air" has ended dives badly. Read the gauge.

Paths to Proper Training

If this page sparked something, the next step is real training: an Open Water course (typically 3–4 days: theory, confined water, four open-water dives) certifies you to 60 feet with a buddy. Advanced Open Water adds deep and navigation dives to 100 feet. Rescue Diver — widely called the most valuable course in recreational diving — teaches you to prevent and manage problems. Every course makes the numbers on this page mean something in your hands, which is the only place they matter. Dive trained, dive with a buddy, dive conservative — and the underwater world is yours for life.