No Chamber for 24 Hours: Freediving's Improvised Answer to Decompression Sickness

Wide underwater view of a freediver descending head-first along a single vertical guide rope into deep blue water, warm surface light fading above and a thin trail of bubbles rising from the mask

The dive itself was unremarkable by the standards of modern competitive freediving: a single descent to 117 metres of seawater, on a competition line, in front of judges. What followed was not. Within minutes of surfacing, the 49-year-old athlete was confused and could not form words properly. His right face sagged. His right arm and leg were weak. The clinical picture read as severe neurological decompression illness—dissolved gas coming out of solution where it does the most damage—and it needed a hyperbaric chamber immediately.

The nearest chamber was an estimated 24 to 48 hours away.

That gap is the subject of a case report published in the September 2026 issue of Diving and Hyperbaric Medicine by Dr. Jake Johnston of the University of British Columbia and colleagues. It arrives at a moment when freediving is pushing past the depths that were once considered the exclusive territory of scuba, and when the specialty that treats its casualties is being asked a question it has not formally answered: what do you do when the treatment is a day away and the patient is in front of you?

The sea as a substitute

With a chamber out of reach, the rescue team turned to oxygen-based in-water recompression, or IWR—a manoeuvre in which the diver breathes 100 percent oxygen from a full-face mask while held at depth, then is walked up slowly on a schedule. An incremental ascent from 18 metres of seawater over roughly 14 and a half minutes produced a substantial recovery. Residual gait instability and a persistent pronator drift prompted a second oxygen recompression five and a half hours later, from 15 metres over 41 minutes, after which the neurological signs resolved completely.

It is, on paper, an excellent outcome. The authors spend much of their discussion explaining why it should not be read as an endorsement. The same report describes its own review of the episode as identifying “serious safety and ethical failures,” and states plainly that the success of this case does not establish that the deeper exposures were necessary or superior to shallower protocols. In-water recompression, they write, is high-risk and demands proper patient selection, trained personnel and favourable conditions. It can cause oxygen toxicity and, in the worst version of events, drowning.

No IWR guidelines exist specifically for freedivers. Protocols that do exist—written for scuba and surface-supplied divers in narrow scenarios—prescribe oxygen breathing at depths of no more than about nine metres for roughly one to three hours. The freediver in this case was recompressed twice as deep as that ceiling.

A pattern, not an outlier

The case is unusual; the behaviour behind it is not. In December 2025, the same journal published a case series from Dr. Nicole Lin at Stanford and colleagues, who interviewed six competitive freedivers about 13 episodes of decompression illness. Six of those episodes were treated with in-water recompression lasting 20 to 90 minutes at depths between 5 and 25 metres, with partial to complete resolution in all six; four of those divers went on to receive hyperbaric oxygen therapy afterwards. One diver was left with significant permanent disability. The authors’ conclusion was blunt: freedivers, often far from medical care, were self-treating with a modality that is “being utilised sometimes without medical oversight,” and guidelines for them should be developed.

A companion survey paper in the same issue adds scale to the problem. Of 36 breath-hold divers surveyed by Dr. Elaine Yu and colleagues at UC San Diego and the Karolinska Institute, half reported experiencing decompression illness; 13 individuals accounted for 21 incidents between 1999 and 2024. Three-quarters of those incidents happened during training, at an average depth of 83 metres, and the most cited contributors were depth, short surface intervals between dives and pulmonary barotrauma. Notably, 62 percent occurred on dives shallower than the diver’s own personal best—a reminder that personal records are not a safety threshold.

The underlying physiology has been documented for decades. A 2023 systematic review in the same journal identified 44 cases of decompression illness after breath-hold diving in the literature and concluded that both decompression sickness and arterial gas embolism—the two mechanisms that make up decompression illness—should be considered genuine risks for this group, exactly as for divers breathing compressed gas. The first report of decompression sickness in repetitive freediving dates to 1958.

Why the chamber still wins

None of this changes what hyperbaric oxygen therapy is: the definitive treatment for decompression illness, and one of the oldest indications on the FDA-cleared list for the therapy. The Undersea and Hyperbaric Medical Society counts decompression sickness among its approved indications, and Medicare’s national coverage determination for hyperbaric oxygen therapy covers its use for the condition. The clinical logic is not in dispute—pressurisation shrinks the offending gas bubbles and high oxygen tensions accelerate nitrogen washout while oxygenating starved tissue.

The variable that matters is time. In the Lin case series, in-water recompression functioned as it is most defensibly used in the literature—as a bridge to a chamber, not a replacement for one. Four of the six divers who underwent it later received HBO. The missing ingredient, in every account, is not efficacy but access: hyperbaric facilities are concentrated in cities, while the world’s deepest freediving happens at pools of blue water reachable only by boat. A second case report in the same September issue makes the other half of the point. A recreational scuba diver who had done eight dives within accepted limits developed life-threatening multisystem decompression sickness with marked haemoconcentration, and needed large-volume intravenous fluids in an intensive care unit attached to the hyperbaric unit. The chamber, in that case, was next door to the ICU. That is not a coincidence; it is a design requirement.

The safety layer the sea cannot provide

Any discussion of chambers has to carry the reminder the FDA issued to health care providers on 25 August 2025. The agency’s letter notes that HBOT devices are Class II devices cleared through the 510(k) pathway, and that it is “aware of recent reports of fires that occurred with HBOT devices that resulted in serious injuries and deaths.” It asks providers to follow manufacturer instructions, maintain fire prevention measures, train and monitor staff, and control prohibited items, including electrical or static-generating devices. A regulated hyperbaric facility, in other words, is a room engineered around a set of risks that includes fire, pressure injury and oxygen toxicity—with monitoring, trained staff and documentation.

Open water offers none of that. It offers a rope, a mask and, in the best case, a physician on a boat who has to decide between a manoeuvre without guidelines and a patient who may not survive the drive. That dilemma is not going to be resolved by another case report with a happy ending. The two 2025 papers both call for formal freediving-specific IWR guidelines; until they exist, every deep-water decompression is a judgement call made at the surface, by whoever happens to be standing there.

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