03 · Equipment
Chamber types: class, occupancy, and shell
Three distinctions get confused constantly — Class A versus B, monoplace versus multiplace, and hard-shell versus soft-sided. Only one of them is a code classification, and it drives most of what a facility has to build.
The code distinction
Occupancy, not marketing terms.
NFPA 99, Chapter 14 classifies chambers by occupancy: Class A is human, multiple occupancy — what the industry calls multiplace. Class B is human, single occupancy — monoplace. Class C is animal, with no human occupancy (UpCodes Chapter 14).
That classification is not a label; it determines what the building has to provide. A Class A installation triggers two-hour fire-rated construction, a deluge and handline fire suppression system, and in-chamber breathing apparatus for every occupant. A Class B installation does not trigger those, but still requires a sprinklered, exclusive-use room.
HSP installs, services and inspects both hard-shell and soft-shell chambers, monoplace and multiplace. What changes between them is the scope of work, the site preparation, and the documentation you should expect back — not the standard of workmanship.
| Requirement | Class A (multiplace) | Class B (monoplace) |
|---|---|---|
| Two-hour fire-rated construction | Required | Not required |
| Deluge plus handline suppression | Required | Not required |
| Sprinklered room | Required | Required |
| Exclusive-use room | Required | Required |
| Emergency decompression from 3 ATA | Less than 6 minutes | Less than 2 minutes |
| Ventilation rate | 3 ft³/min per occupant not on an overboard dump system | Per the Class B ventilation provisions of the chapter |
| In-chamber breathing apparatus per occupant | Required, supplied independently of the chamber atmosphere | Not applicable |
| Ground integrity verification Voluntary | UHMS criteria: at least weekly | UHMS criteria: before each patient treatment |
Sources: UpCodes Chapter 14, UpCodes chamber ventilation provisions, NFPA Journal and the UHMS accreditation manual. The ground-integrity row is a UHMS accreditation criterion citing the UHMS guidelines, not NFPA.
Pressure
What pressures are actually in play
Chapter 14 covers medical and experimental use at gauge pressures from 0 psi to 100 psi (UHMS quoting the current edition scope statement). The professional society’s position statement on hyperbaric oxygen states that the patient must be placed entirely within a hard-sided chamber meeting ASME PVHO-1 and NFPA 99, at a pressure of not less than 2.0 ATA, breathing medical-grade oxygen of greater than 99.0 percent purity, and that scientifically supported hyperbaric treatments are usually delivered at pressures between 1.9 and 3.0 ATA (UHMS HBO indications).
Both codified emergency-decompression provisions are written from 3 ATA, which is a useful indicator of the design envelope for clinical chambers (UpCodes Chapter 14). Manufacturer catalogues commonly list models at 2.0, 2.4 and 3.0 ATA with one to four seats (HPO Tech) — those are one manufacturer’s product figures, not standard values, and should never be presented as code requirements.
The cleanest technical line for the shell question is the PVHO-1 threshold: the standard applies to vessels with a pressure differential exceeding 2 psi (FDA’s record for PVHO-1-2023).
Soft-sided chambers
The honest regulatory picture
This is a genuinely contested area. Rather than pick the convenient version, here is what the primary documents say, and where the dispute sits.
Class II devices, narrow indication
Public 510(k) summaries for soft-sided “mild hyperbaric” chambers describe devices for pressures less than 5 psi, urethane-coated nylon with a zipper closure, inflated with atmospheric air, relief valves set at roughly 3 to 4 psi, and operating pressures of about 3 psi (1.2 ATA) to 4 psi (1.3 ATA). The indications for use named in those clearances are acute altitude or acute mountain sickness, as prescribed by or under the direction of a physician.
The Gamow bag lineage
Those clearances cite the Gamow Hyperbaric Bag and related models as predicate devices. FDA’s public records for the predicate family remain available.
Code applies, says UHMS
UHMS’s published position is that soft-sided bag chambers and the facilities operating them are subject to the same safety requirements as hard-sided chambers, relying on the chapter’s 0 to 100 psi scope and on NFPA 101 extending NFPA 99 to hyperbaric facilities in all occupancies.
UHMS goes further, stating that many soft-sided chambers on the market are not registered with FDA; that even those that are do not comply with NFPA 99, Chapter 14 and are not designed, fabricated and certified to ASME PVHO-1; that claims of equivalence to the Gamow bag are misleading because that device delivered only compressed air and was intended for acute mountain sickness at altitude rather than certified for use with supplemental oxygen; that soft chambers are typically not compressed with the certified medical air grades the code requires; and that many are sold with oxygen concentrators, which UHMS describes as a device not authorised for use with fabric soft-sided chambers. The same article states that Health Canada has banned soft-sided bag chambers in Canada, and cites incidents including a death from asphyxia in an unattended home mild chamber in North Carolina and a soft bag chamber rupture with an occupant inside in India in September 2024 (UHMS consumer warning). A national society outside the United States makes the same narrower point: low-pressure fabric chambers operating below 1.4 ATA hold a 510(k) clearance for acute mountain sickness only and are designed to be compressed with air (SAUHMA position statement).
Soft chambers typically operate at 2 to 4 psi — above PVHO-1’s 2 psi threshold — which is precisely why the applicability argument exists rather than being settled by the numbers.
A proposed Tentative Interim Amendment to NFPA 99-2024, TIA No. 1735, would have created a new “Category 4 Hyperbaric Facilities” section with reduced requirements for mild chambers — classifying the chamber as Class B, setting a 1 ft³/min minimum ventilation rate and a two-minute emergency depressurisation capability, requiring a 2-A:10B:C extinguisher in the room, and defining a Category 4 threshold of chamber gauge pressure less than 34.5 kPa (5 psi) with oxygen concentration less than 25 percent. Its substantiation argued that no standards exist for the operation of soft-sided chambers (the TIA ballot memo). The final technical committee ballot rejected it: the results show the TIA did not achieve the three-quarters majority needed on either technical merit or emergency nature, with 0 agree and 17 disagree on both items out of 20 eligible voters (the final ballot results).
Where that leaves an owner. Hard chambers used clinically are PVHO-1 stamped pressure vessels operating at roughly 2.0 to 3.0 ATA on prescribed medical-grade oxygen, installed and operated to NFPA 99, Chapter 14. Soft-sided fabric chambers are lower-pressure, air-filled, Class II prescription devices whose clearances name acute mountain or altitude sickness. Whether Chapter 14 applies to them is unresolved in code: the professional society says yes, and NFPA’s own technical committee rejected the proposed carve-out that would have said otherwise. Nobody should tell you a soft chamber is code-compliant, PVHO-stamped, or interchangeable with a hard chamber. We will service either, and we will document which one you have.
Hyperbaric Service Pros installs, services, and maintains hyperbaric equipment. We are not a medical facility and do not provide medical advice or treatment. Technical information on this site is general reference only — always follow your chamber manufacturer's documentation and the codes enforced in your jurisdiction.
Sources
Every claim on this page, traced to its source
- NFPA 99 Chapter 14, Hyperbaric Facilities — UpCodes public viewerhttps://up.codes/viewer/centers-for-medicare-and-medicaid-services/nfpa-99-2012/chapter/14/hyperbaric-facilities
- NFPA 99 Chapter 14, chamber ventilation provisions — UpCodeshttps://up.codes/s/chamber-ventilation
- NFPA Journal, “Under Pressure,” Brian O’Connor, Aug. 23, 2021https://www.nfpa.org/news-blogs-and-articles/nfpa-journal/2021/08/23/nfpa-13-august
- UHMS Clinical Hyperbaric Facility Accreditation Manual, 4th ed.https://www.uhms.org/images/Accreditation-Documents/Fourth_Edition_UHMS_Accreditation_Manual_Final.pdf
- UHMS, “Consumer Warning: The Dangers of Soft-Sided Bag Chambers”https://uhms.org/pressure-other-articles/1542-consumer-warning.html
- UHMS HBO indications and position on hyperbaric oxygen deliveryhttps://uhms.org/resources/featured-resources/hbo-indications.html
- FDA recognized consensus standard record — ASME PVHO-1-2023https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfStandards/detail.cfm?standard__identification_no=45593
- FDA product classification database — “chamber, hyperbaric,” product code CBFhttps://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=95
- FDA 510(k) summary K072757 — soft-sided mild chamberhttps://www.accessdata.fda.gov/cdrh_docs/pdf7/K072757.pdf
- FDA 510(k) summary K051759 — soft-sided mild chamberhttps://www.accessdata.fda.gov/cdrh_docs/pdf5/K051759.pdf
- FDA 510(k) record K874752 — Gamow Hyperbaric Baghttps://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpmn/pmn.cfm?ID=K874752
- SAUHMA position statement on low-pressure fabric chambershttps://www.sauhma.co.za/sauhma-position-statement.htm
- Proposed NFPA 99 TIA No. 1735 — ballot memohttps://www.nfpa.org/api/files?path=/files/AboutTheCodes/99/99_2024_HEA_HYP_Log1735_tiaballot.pdf
- NFPA 99 TIA No. 1735 — final technical committee ballot resultshttps://docinfofiles.nfpa.org/files/AboutTheCodes/99/99_2024_HEA_HYP_Log1735_tiaballot_final.pdf
- HPO Tech chamber specifications (manufacturer catalogue example)https://www.hpotech.com/hyperbaric-chambers/mediterranean/
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