The 3-minutes-safety-stop

Recently, a very experienced diving instructor asked me how useful the classic 3-minute safety stop actually still is from today’s perspective. It’s an intriguing question—because the 3-minute safety stop at 5 meters is practically standard practice in recreational diving today. It’s performed millions of times every year. Hardly any recreational dive during the holidays ends without the memorable rule: “Three minutes at five meters at the end of every dive.” Many dive computers count it down automatically, and many divers perform it without even thinking about it anymore.

"3m-hazard-stopp"

Not Actually a Decompression Stop

One important point is often overlooked: by definition, the classic safety stop is not actually a decompression stop. It is performed during no-decompression dives—that is, dives that, in theory, could be ended immediately without mandatory decompression. That is precisely why it is not called a “decompression stop,” but a “safety stop.” But then—what is its purpose?

The historical origins

The history of the safety stop is closely linked to the development of modern recreational diving. As early as the 1970s, Andrew Pilmanis investigated the relationship between ascent speed, short intermediate stops, and venous gas bubble formation after dives. Ultrasound examinations revealed that slower ascents or short stops just before the surface were associated with a lower venous bubble load (venous gas embolism, VGE). Particularly relevant was the observation that the final meters of the ascent have a disproportionately large influence on bubble formation. These findings contributed significantly to establishing the idea of a short safety stop at the end of no-decompression dives.

In the 1980s, the safety stop increasingly appeared in recreational diving training, including in the PADI Open Water Manual. Later, the well-known PADI campaign “SAFE Diver – Slowly Ascend From Every Dive” finally popularized the concept.

Donna Uguccioni’s master’s thesis in 1994 confirmed Pilmanis’s aforementioned observation. Using Doppler ultrasound, she examined VGE after dives and was able to show that divers who performed a safety stop tended to exhibit less VGE than divers who did not stop. This study is still frequently cited today as an argument in favor of the safety stop.

How strong is the evidence really?

However, we need to be honest here: The evidence that a 3-minute stop at 5 meters actually prevents clinically manifest DCS is thin—to put it mildly. The safety stop is thus less a hard scientific certainty than a plausibly justified safety measure.

Why the last few meters are so critical

From a physiological perspective, the classic safety stop is an interesting hybrid. On the one hand, it actually functions like a small decompression stop: the diver remains at moderate ambient pressure for a few minutes, allowing dissolved inert gas to be exhaled further. On the other hand, it fulfills a second, likely equally important function: it prevents a rapid final ascent to the surface.

This principle can already be found in the work of Albert A. Bühlmann: In his tables, he recommended a brief one-minute stop at 3 m for no-decompression dives. However, this was explicitly not about additional decompression in the strict sense, but rather about breaking the ascent speed immediately before reaching the surface.

Even back then, the idea was present that the final meters of the ascent are particularly critical from a physiological standpoint—not only because of the potential formation of microbubbles, but also due to the risk of barotrauma. The safety stop mitigates this final pressure drop, so to speak, mechanically by forcing the diver to interrupt the ascent. In this way, it also allows more time for pressure equalization and protects against barotrauma.

That is why it makes no sense to perform the safety stop at 5 m cleanly and with discipline, only to then rush the final meters to the surface. It is precisely the final section after the safety stop that remains the most critical part of the entire ascent in terms of pressure physics. The actual benefit of the safety stop therefore only fully unfolds when the final meters are also conducted slowly and in a controlled manner.

Why not deeper?

A safety stop should not be performed at just any depth. A deeper safety stop at 10 m may intuitively seem safer, but it can be physiologically counterproductive. According to Bühlmann’s reasoning, during a compressed-air dive in the sea at depths of less than 6.4 m, there is no longer any on-gassing that would exceed the supersaturation tolerance of even the most sensitive tissues.

This is the actual reason why the classic safety stop is not performed at a greater depth. At 5 m, inert off-gassing occurs from the more saturated tissues without (slow) tissues on-gassing to a critical extent.

To be fair, however, it must be noted that this consideration is of a rather academic nature in the context of a true no-decompression dive. The additional inert gas uptake during a short stop at 5 m is unlikely to have any clinical relevance in recreational diving scenarios.

But even this shallow depth has its practical drawbacks. All divers are familiar with the problem: maintaining perfect buoyancy at 5 m is significantly more difficult than at 10 m. Small changes in volume in the BCD or lungs immediately lead to significant depth fluctuations. Especially in the presence of waves or currents, there is therefore a risk of accidentally ascending to the surface. And from a decompression physiology perspective, this is precisely what is undesirable, as it results in the loss of controlled pressure reduction.

The safety stop thus exists in a tension between theory and practice. Too deep is undesirable due to further saturation; too shallow increases the risk of unintended surface contact. Five meters ultimately represents a pragmatic compromise.

Distinction from technical diving

It is also important to clearly distinguish this from technical diving. In recreational diving, the safety stop is, by definition, a voluntary additional stop within the no-decompression limits. In technical diving, however, true decompression is performed planned, model-based, often using decompression gases. There, stops are no longer an additional safety measure but an integral part of the dive. A technical decompression stop on oxygen or nitrox has a completely different physiological significance than the classic PADI safety stop.

Diving Practice

In addition, the safety stop often serves very practical functions that have nothing to do with decompression physiology. For example, it can be used to reunite a buddy team or to gather an entire group together one last time before surfacing. Especially under demanding conditions—such as drift dives in the ocean or boat dives—this brief pause immediately before surfacing can be very valuable. The safety stop creates a moment of calm and orientation before returning to the surface, where waves, currents, or boat traffic can pose additional challenges.

Conclusion

In conclusion, it should be noted that despite limited hard clinical evidence, the classic safety stop appears physiologically plausible and practically sensible. It is likely to provide an additional safety margin, particularly during repeated, deeper, or borderline no-decompression dives. As aptly put in Diving and Subaquatic Medicine:

“Such stops are probably useful in reducing the incidence of DCS on routine no decompression dives.”

(Edmonds C, Bennett M, Lippmann J, Mitchell S. Diving and Subaquatic Medicine, p. 160), CRC-Press, Kindle-Version

Perhaps it is precisely this cautious “probably useful” that best describes the safety stop: not a magic bullet against decompression sickness, but a simple, sensible, and likely helpful precaution at the end of a recreational dive.