04 · Safety
Oxygen enrichment and ignition control
Oxygen does not burn. It makes other things burn far more readily, and pressure compounds the effect. That single fact drives most of the material, electrical and housekeeping rules in hyperbaric practice.
The physics
An oxidiser, not a fuel.
NFPA’s own article makes the two points a service contractor can state without embellishment: oxygen is an oxidiser rather than a flammable gas — it does not burn itself, but it dramatically accelerates combustion — and materials that are perfectly safe at atmospheric conditions, including silicone rubber, some lubricants and even flame-resistant fabrics, can ignite at elevated pressure and elevated oxygen concentration (NFPA Journal).
That is why the rules in this field are about materials and static rather than about open flame. Nobody brings a match into a chamber. The realistic ignition sources are a spark from a cord or caster, a static discharge from clothing, or a component that is fine in room air and not fine in an enriched, pressurised atmosphere.
FDA’s Letter to Health Care Providers states that the agency is aware of reports of serious injuries and deaths with use of HBOT devices, and of recent reports of fires with HBOT devices resulting in serious injuries and deaths, adding that the root cause of these events is not currently known (FDA Letter to Health Care Providers).
The threshold
23.5 percent does two things
| Monitoring trigger | Continuous oxygen monitoring is required in Class A chambers whenever breathing mixtures greater than 21 percent oxygen by volume are used. |
|---|---|
| Alarm threshold | Audible and visual alarms must indicate volumetric oxygen concentrations in excess of 23.5 percent. |
| Antistatic procedures | The same 23.5 percent figure triggers antistatic procedures: the chapter requires antistatic procedures whenever chamber atmospheres exceeding 23.5 percent oxygen by volume are used. |
| Patient grounding | Patient grounding through a high-impedance conductive pathway is required in Class A and Class B chambers operating above 23.5 percent oxygen. |
| Mixed consoles | Consoles or module spaces containing both oxygen piping and electrical equipment must be continuously ventilated, or continuously monitored for excessive oxygen, whenever the electrical equipment is energised. |
Sources: UpCodes Chapter 14 and the UHMS accreditation manual. A monitor that alarms is only useful if someone verified it recently — which is why oxygen monitoring belongs in your documented maintenance program rather than in the “it has always worked” category.
Materials and static
What is prohibited, and why
- Textiles. Silk, wool and synthetic textiles are prohibited in Class A and Class B chambers; 100 percent cotton, or a cotton and polyester blend, is permitted. FDA independently advises dressing patients in hyperbaric-compatible materials such as cotton, noting that wool and synthetics produce more static.
- Footwear. Shoes with ferrous nails are prohibited in Class A chambers.
- Metals. Cerium, magnesium and magnesium alloys are prohibited from the chamber interior, and metals capable of impact sparking are not used for casters or furniture leg tips.
- Conductive path integrity. Conductive devices — leg tips, tires, casters — must be inspected free of wax, lint or other insulating material, and lubricants must be oxygen-compatible and flame-resistant.
- Hull grounding. Chamber hulls are grounded per the National Electrical Code, and resistance between the grounded hull and electrical ground shall not exceed 1 ohm.
- Prohibited items. Smoking, open flames and hot objects are prohibited near the chamber. Personal warming devices, cell phones and pagers, sparking toys and personal entertainment devices are prohibited inside it.
- Lubricants and paper. In-chamber equipment requiring lubrication uses oxygen-compatible, flame-resistant lubricant, and paper taken into a Class A chamber is stored in a closed metal container emptied after each operation.
Sources: UpCodes Chapter 14, the UHMS accreditation manual and the FDA letter.
UHMS’s Safety Committee notes that building HVAC affects the ability to control humidity and temperature, which can affect the control of static electricity in the chamber room (UHMS Safety Committee FAQ). That is a professional-society observation, not a numeric code requirement — no relative humidity range for the chamber room was found codified in the material reviewed for this library. If a specification sheet gives you a range, it is your manufacturer’s, and it is the one to work to.
FDA recommendations
What the 2025 letter asks facilities to do
FDA’s recommendations in that letter are worth reading in the original, and are short. They include following the manufacturer’s instructions for use; ensuring fire prevention and safety measures are in place, with explicit awareness that there is a heightened risk of fire with use of oxygen at high concentration; ensuring proper grounding equipment is used; ensuring that manufacturer-recommended cleaning procedures, maintenance intervals and safety checks are followed for each device; ensuring staff are trained, and monitoring and supervising patients during treatment; keeping prohibited items, including electrical or static-generating devices, out of the chamber; and dressing patients in hyperbaric-compatible materials such as cotton, since wool and synthetics produce more static. The letter’s additional resources section points readers to NFPA 99 and ASME PVHO-1 (FDA Letter to Health Care Providers, August 25, 2025).
Three of those recommendations are directly a service question rather than a clinical one: grounding, manufacturer-specified maintenance intervals, and functioning safety checks. Those are what a field-service visit exists to verify and record.
Hyperbaric chambers are regulated as devices: the device name is “chamber, hyperbaric,” the regulation is 21 CFR 868.5470, the class is II, the submission type is 510(k), the product code is CBF, and the classification record lists the device as life-sustaining or life-supporting (FDA product classification record). FDA states that HBOT devices are Class II medical devices cleared through the 510(k) process, identifiable by searching product code CBF in the 510(k) database (the same FDA letter). Note what that clearance is and is not: it is a device clearance based on substantial equivalence to a predicate device, tied to the indications in that submission — not an endorsement of a facility, an operator, or a service company. UHMS accreditation criteria require the facility to hold a copy of the manufacturer’s clearance letter for the chambers in use (UHMS accreditation manual).
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 Journal, “Under Pressure,” Brian O’Connor, Aug. 23, 2021https://www.nfpa.org/news-blogs-and-articles/nfpa-journal/2021/08/23/nfpa-13-august
- 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
- UHMS Clinical Hyperbaric Facility Accreditation Manual, 4th ed.https://www.uhms.org/images/Accreditation-Documents/Fourth_Edition_UHMS_Accreditation_Manual_Final.pdf
- UHMS Safety Committee FAQ — standards and codeshttps://www.uhms.org/tl/resources/featured-resources/medfaqs-frequently-asked-questions-faq/safety-technical/standards-and-codes.html
- FDA Letter to Health Care Providers, Aug. 25, 2025 — safe use of HBOT deviceshttps://www.fda.gov/medical-devices/letters-health-care-providers/follow-instructions-safe-use-hyperbaric-oxygen-therapy-devices-letter-health-care-providers
- FDA product classification database — “chamber, hyperbaric,” product code CBFhttps://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfpcd/classification.cfm?id=95
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