Soft vs hard hyperbaric chambers: 1.3 ATA and 2.0 ATA
Compare chamber pressure, oxygen purity and the clinical definition before choosing equipment.
Updated 4 November 2026 · HBO₂ Health
How the options compare
Two numbers decide the oxygen dose: the pressure in the chamber and the purity of the oxygen you breathe. Lower either one and the dose drops.
In 2026 the Undersea and Hyperbaric Medical Society set out what counts as hyperbaric oxygen treatment, or HBO₂. It has to be prescribed and supervised by a physician. It takes place in a hard chamber built to ASME PVHO-1 and NFPA 99, at no less than 2.0 ATA, with medical oxygen above 99% purity. UHMS position statement.
That definition is a useful test for any chamber you are considering.
| Type of chamber | Pressure | What you breathe | Meets the UHMS definition |
|---|---|---|---|
| Soft, inflatable chamber | Around 1.3 ATA | Air, or oxygen from a concentrator | No. The pressure is too low. In the US these are cleared for acute mountain sickness only. |
| Hard “mild” chamber | 1.3 to 1.5 ATA | Oxygen from a concentrator, typically 90 to 95% | No. Both the pressure and the oxygen purity fall short. |
| Oxygen-filled monoplace | 2.0 ATA and up | The whole cabin is filled with oxygen | Yes, when built to PVHO-1 and NFPA 99. One patient, lying down. |
| FINK FESL | Up to 2.0 ATA | 100% medical oxygen through a mask. The cabin is filled with air. | Yes, at 2.0 ATA with physician-prescribed and supervised treatment. One to four people, seated. |
Concentrators are a common shortcut. Even a medical-grade concentrator supplies around 93% oxygen, which is below the UHMS bar. Our medical oxygen guide explains why.
FESL chambers deliver oxygen at up to 2.0 ATA, the minimum pressure in the UHMS definition. Some emergency indications, such as decompression sickness and gas embolism, are usually treated at higher pressures in hospital chambers. The doctor prescribes the pressure for each patient.
Compare the prescribed treatment
Purity multiplied by pressure is a useful starting point for comparing oxygen exposure. It does not establish a clinical outcome. The indication, session schedule, mask fit and medical oversight also matter. Ask for the protocol and the equipment documentation together.
Plan your FINK chamber installation
Tell us your country, intended setting and preferred capacity. We will help you work through the model and installation requirements, with an initial project budget. The final scope and price are confirmed in a written quotation.