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RecreationalSCUBA decompression

Recreational diving produces the largest body of dive-profile data in the public record and the weakest outcome labels attached to it. Most profiles come from consumer dive computers. Few carry any recorded health outcome, and almost none carry a measurement of the diver.

The exposure envelope

What the profile keeps available is what defines recreational diving. The numbers below come from published training material, and they describe the exposures the evidence was drawn from.

Depth
Training limits are commonly published at 40 m, with 18 m or 20 m set for entry-level certification.
Breathing gas
Air, or nitrox at oxygen fractions up to 40 percent. Helium is outside the recreational envelope.
Oxygen exposure
Training material commonly states a working limit of 1.4 bar for inspired oxygen partial pressure.
Ascent
The profile keeps a direct ascent to the surface available throughout. No decompression ceiling is planned.
Repetition
Several dives a day across consecutive days is a common pattern in logged recreational data.
Instrument
A consumer dive computer, usually running a dissolved-gas model the manufacturer names but does not fully specify.

What the evidence supports

Claims about recreational decompression sit at very different strengths. Each column below holds claims that the public evidence carries to roughly the same degree.

  • Well supported

    • A dissolved-gas model reproduces the no-stop limits of the table it was fitted to. That is a property of the fit, and it can be checked against the published table.
    • Two dive computers can report different remaining no-stop time on one profile. The difference is reproducible once the version and the configuration constants are known.
    • Breathing nitrox at a fixed depth lowers the inert gas fraction, so the modelled loading falls.

  • Partly supported

    • Nitrox lengthens the modelled no-stop time at a given depth. How much any resulting change in outcome risk amounts to is far less well established.
    • Ascent rate changes the modelled tissue state. Studies connecting a specific ascent rate to a measured change in symptom incidence are small.
    • Bubbles detected after a dive track exposure severity. Their value in predicting an individual outcome stays weak.

  • Open

    • Whether a safety stop measurably alters decompression sickness incidence. The event is too rare in most published cohorts for the question to be settled.
    • How much of the risk in a multiday pattern is carried by the last dive, and how much by the accumulated sequence before it.
    • Which diver-side measurements would improve a risk estimate enough to justify collecting them at scale.

Reading a dive computer as a model

Four separable things produce the remaining time on a dive computer display: the model family, the model version, the configuration constants and the implementation. Change any one of them and the displayed number moves.

Manufacturers publish the family and sometimes the version. Configuration constants and implementation detail are frequently withheld, so two units that name the same model can still disagree. OpenDeco records the four fields separately, so a disagreement between two units can be traced to the field that differs.

How a model implementation is reconstructed

Limits of the evidence

  1. Decompression sickness is rare in recreational diving. A study needs a large denominator before a difference in incidence becomes measurable at all.
  2. Most public profile sets record the dive and not the diver. Age, thermal state, hydration and exercise are absent from the record.
  3. Symptom data is usually self-reported, so it carries recall effects and reporting incentives.
  4. A profile that ended in good health is evidence about that dive. It does not validate the model that produced the numbers on the display.
  5. Divers select their own exposures, so the profiles in a dataset are not a random sample of the dives that were possible.

OpenDeco publishes research material. This page describes what the evidence supports. It is not a dive plan, a table or a recommendation about any dive.

Read the research safety statement

The technical track covers the exposures this page leaves out.