Mild Hyperbaric Oxygen Therapy

Chamber fires in the clinical record

A historical review gives the earliest systematic count of harm in hyperbaric chambers in these sources. Sheffield and Desautels counted 77 human deaths in 35 hyperbaric chamber fires reported between 1923 and 1996 in Asia, Europe and North America. Of those 35 fires, 25 occurred in clinical hyperbaric chambers, and the authors report no fire fatalities in North American clinical chambers over that period.

The same review links the fatal fires to oxygen levels and ignition sources. Each fatal fire occurred in an atmosphere above 28 percent oxygen with burnable material present, and chambers pressurized with air were the only ones with survivors. The authors apply this history to safer chamber operation, which is relevant to any chamber, clinical or not.

Origins of mild chambers in wellness settings

The sources reviewed do not document when or where low-pressure soft-sided chambers first came into wellness use. The Undersea and Hyperbaric Medical Society (UHMS) states that treatments at minimally elevated chamber pressures have spread to wellness centers and health spas outside medical facilities, and that these treatments are generally not physician-prescribed or supervised.

Morningstar and Strauchman describe mild treatment as a category separate from clinical hyperbaric oxygen, used mainly for wellness and recovery. Johnson-Arbor, in a 2026 narrative review, describes the mild form as physiologically different from the clinical treatment rather than as a shallower version of it. Neither review dates the start of commercial use.

Mild and clinical pressure

Johnson-Arbor describes traditional hyperbaric oxygen treatment as the inhalation of 100 percent oxygen in a pressurized chamber above sea-level pressure. Mild treatment uses shallower treatment depths and lower oxygen concentrations. The UHMS describes mild hyperbaric treatment as exposures below 1.5 atmospheres absolute (ATA) and states that its benefit is unproven.

The sources do not agree on the boundary. Morningstar and Strauchman cite the UHMS as placing clinical hyperbaric oxygen above 1.4 ATA, and they give a mild range of 1.1 to 1.49 ATA in their classification table. Because the threshold decides which chambers count as mild, a reader should check the primary UHMS text for the exact wording before relying on either figure.

Soft-sided and hard-sided chambers

Murray describes two construction types marketed as mild. Soft-sided chambers are fabric enclosures, and hard-sided mild chambers are designed for operational pressures of about 3 to 5 psi. Morningstar and Strauchman describe soft-sided chambers as typically made of PVC or nylon and generally regulated as wellness devices.

The distinction matters for the safety discussion. Clinical hyperbaric chambers are described as medical devices, while Morningstar and Strauchman state that soft-sided chambers are not FDA-approved for conditions that require increased pressure. Murray and Johnson-Arbor both treat chamber construction and fire-safety standards as relevant to mild and clinical chambers alike.

Mild treatment as a separate term

Morningstar and Strauchman argue that hyperbaric oxygen therapy and mild hyperbaric oxygen therapy are not synonyms. They say that writing that blurs the two can mislead readers about chamber pressure and oxygen levels, and that these details are often not disclosed. The trial literature uses abbreviations such as mHBOT for the mild form.

Chamber and gas settings

In the mild form, the session takes place in a chamber with a pressure only slightly above sea-level pressure. Morningstar and Strauchman report that mild chambers typically use ambient air or concentrator oxygen, with an oxygen partial pressure of roughly 250 to 400 mmHg in their table, and that one soft chamber at about 1.3 ATA gave an oxygen partial pressure near 80 mmHg.

In the controlled trial by Rossignol and colleagues, the treatment arm breathed 24 percent oxygen at 1.3 atmospheres, and the control arm breathed 21 percent oxygen at 1.03 atmospheres in slightly pressurized room air. The two-arm design compared a mild pressure with a near-ambient pressure, and it does not describe a wellness session.

Who delivers the session

The UHMS states that mild treatments are offered at wellness centers and health spas, are generally not physician-prescribed or supervised, and that some operate without proper fire-safety or chamber-construction standards. Murray describes the practice as marketed to the public with claims about efficacy and safety that the author regards as misleading.

The sources reviewed do not describe a standard session format for wellness use, and the trial protocols cited here differ from one another. This page therefore does not describe a protocol, and readers should not treat any trial format as guidance for a session.

Wellness, recovery and sleep

Morningstar and Strauchman describe mild treatment as used mainly for wellness and recovery. They report positive signals in exercise recovery and some other areas, but they state that these need replication before they can be relied on. A 2026 randomized trial in healthy young men who had lived at 4,300 meters tested mild treatment for sleep quality and cognition.

Johnson-Arbor reports that mild treatment may benefit peripheral microcirculation, parasympathetic activity and metabolism, but that it has not been studied extensively as a wound treatment. These are proposed mechanisms and aims rather than established outcomes, and the reviews cited here do not show that they translate into health benefit for the general population.

Autism and brain injury

Mild treatment has been proposed for autism, and the controlled trial by Rossignol and colleagues is the main mild-pressure study in this area. Sakulchit, Ladish and Goldman advise against recommending hyperbaric oxygen for children with autism. They note that commercial advertising has suggested good results, and that parents often ask about the approach.

For brain injury, Morningstar and Strauchman note that in post-concussion trials both the active and sham groups often improved. That pattern suggests that expectation or the sham condition may influence outcomes. The sources reviewed did not identify a verified controlled trial of mild treatment for brain injury, so this claim should be checked against the primary trial reports before it is repeated.

Controlled trials at mild pressure

Rossignol and colleagues randomized 62 children with autism, aged 2 to 7 years, to 40 hourly sessions at 1.3 atmospheres and 24 percent oxygen, or to slightly pressurized room air. The authors report significant improvement in physician-rated overall functioning, receptive language, social interaction and eye contact in the treatment group, and they describe the treatment as well tolerated.

The same trial reports that the gains were not uniform across scales. In a post-hoc analysis, children over age 5 and children with lower initial severity had the most robust improvements. Sakulchit and colleagues state that only one randomized trial reported benefit and that this result has not been repeated. Morningstar and Strauchman describe the Rossignol trial as finding no significant benefit, which conflicts with the abstract of that trial. The reason for the difference is not clear from the sources read.

Healthy adults and athletes

Lin and colleagues randomized 60 healthy young men who had lived at 4,300 meters for at least six months to mild treatment or a control condition for five days. The mild group had a larger reduction in Pittsburgh Sleep Quality Index scores, with an adjusted mean difference of minus 1.08 (95 percent confidence interval minus 1.76 to minus 0.46), and higher accuracy on a working-memory task.

This is a single trial in a small sample of healthy adults, and its abstract does not state the chamber pressure. The findings therefore cannot be assigned to a specific mild pressure or applied to other populations. Morningstar and Strauchman summarize mild-treatment research as limited, mostly small pilot or uncontrolled studies of poor methodological quality, with mixed results.

Reviews and related hyperbaric research

Tu and colleagues pooled 17 studies with 890 children and adolescents with autism who received hyperbaric oxygen therapy, and they report moderately large reductions in core autism symptoms (standardized mean difference minus 0.66). The abstract describes poor study quality and high heterogeneity, and it does not state the chamber pressures. These pooled findings concern hyperbaric oxygen therapy in general and should not be transferred to mild pressures.

Morningstar and Strauchman argue that air at pressures below 1.5 ATA is not physiologically inert, and that it should not be used as a true placebo in trials. This point bears on how any mild-pressure study is read, because a control arm at near-ambient pressure may still produce a physiological effect. The narrative reviews cited here are not systematic and do not report pooled effect sizes for mild treatment.

Fire and oxygen enrichment

Fire is the hazard most consistently described. Johnson-Arbor reports that both mild and traditional hyperbaric treatment are associated with potentially life-threatening events, including chamber explosion or fire, and that adherence to safety standards is not universally mandated and may vary among facilities. Murray lists fire hazards among the risks of mild chambers.

The historical fire record concerns enriched oxygen. Sheffield and Desautels report that each fatal chamber fire occurred in an atmosphere above 28 percent oxygen with burnable material present. The mild sessions in the trials cited here used 21 to 24 percent oxygen, so the fatal-fire pattern does not map directly onto them. The reviews still identify fire as a hazard in mild chambers, and the historical figures should not be read as a rate for wellness sessions.

Barotrauma, equipment and standards

Murray describes the risks of soft-sided and hard-sided mild chambers as including otic and pulmonary barotrauma, suffocation, structural failure and, in extreme cases, death. The same review states that the chambers do not meet the NFPA 99 and NFPA 101 codes or the ASME-PVHO standards it lists. The abstract gives no incidence figures, so the frequency of these events cannot be stated from that source.

Kot describes medical devices used inside European hyperbaric chambers and reports that a wide range of non-CE-certified equipment is used there. The same review notes that implanted devices can malfunction under pressure, and that defibrillation inside a chamber remains hazardous because of fire risk. This review concerns clinical chambers, so it is offered here as context for equipment safety rather than as a description of wellness sessions.

Suitability and care boundaries

Morningstar and Strauchman identify misleading claims, non-disclosure of chamber pressure and oxygen levels, and possible delays in evidence-based care as the main concerns in this setting. Murray raises the ethical point that patients may not be fully informed of the limits and risks of these devices.

This page is educational and does not assess any individual's suitability. Sources identify implanted devices, ear and lung conditions, and unsupervised sessions as factors to review with a clinician before any pressurized exposure. Pressurized sessions should not replace assessment or treatment that a clinician has recommended, and a person with symptoms should seek care through the usual route.