A used chamber is a pressure vessel with an undocumented history attached. The documents matter more than the shell, and they can be checked before you travel — which is why they are group one. The walk-away lines are deliberately blunt: they are the conditions where no price is a good price.
This is an equipment inspection list, not a safety certification. For a rigid vessel, engage someone qualified to inspect pressure equipment. We do this work commercially, which is disclosed below.
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Commercial interest: Hyperbaric Service Pros inspects, installs and services hyperbaric chambers commercially and also sells equipment, so we benefit both when you buy used and when you buy new. The walk-away conditions below are the ones we apply to our own purchases.
01 · Documents — do these first, before you drive anywhere 0/6
Look the number up in FDA's own 510(k) database for product code CBF and confirm the applicant name matches the brand on the chamber. FDA classified a Class 2 recall of one chamber with determined cause 'No Marketing Application'.
Walk away ifNo K-number, or a K-number registered to an unrelated company that the seller cannot explain.
FDA recognises ASME PVHO-1 (pressure vessels for human occupancy) and NFPA 99 as consensus standards for this product code.
Walk away ifA rigid chamber with no PVHO paperwork and no manufacturer able to supply it.
Dates, pressures, who performed it, and what was found. A used vessel with no test history is an unknown, not a bargain.
Walk away ifSeller says testing 'isn't required for this type' and cannot name who would perform it.
A published post-construction check list for hyperbaric installations covers the pressure vessel, electrical systems, instruments, mechanical equipment, piping, air conditioning, hygiene testing and operating rules — not the shell alone.
Walk away ifNo records for compressor, concentrator, valves or electrical, only for the shell.
Is the manufacturer still trading, and will it sell parts and manuals to a second owner?
Walk away ifManufacturer will not confirm parts availability for that serial number.
Search FDA's MAUDE database by product code CBF and by model name. Twelve death reports are indexed under CBF; the two most recent both involve one specific hard-shell model during unsupervised self-treatment.
Walk away ifModel appears in death or serious-injury reports and the seller has never heard of them.
02 · Pressure boundary 0/5
Look across the acrylic at a shallow angle in bright light for fine surface cracking, cloudiness or milkiness around the edges and around any bolt holes. Crazing in an acrylic pressure window is a structural finding.
Walk away ifAny crazing, chip or star crack in an acrylic viewport. Do not accept 'it's only cosmetic'.
Flattening, hardening, glazing, tackiness, splits at the mould line, or debris embedded in the sealing face. Get the part numbers and confirm they are still sold before you buy.
Walk away ifSeal profile is obsolete and no replacement source exists.
Full length of every zipper, both directions, under light tension. Check heat-sealed seams for delamination, and the urethane coating for abrasion or crazing at fold lines. One manufacturer's shell is described as double-sided 44 oz urethane-coated polyester with a ballistic nylon jacket — inspect both layers.
Walk away ifAny zipper that binds, skips or shows separated teeth. Any seam delamination.
Weld seams, penetrations, port bosses, and the inside face of the door. Look for corrosion at penetrations, distortion around the door frame, and paint bubbling that hides pitting.
Walk away ifCorrosion at any penetration or weld, or evidence of a repair with no documentation.
Open and close it twenty times. Latch engagement, hinge play, and any interlock that prevents pressurisation with the door unsecured.
Walk away ifInterlock has been bypassed, removed or 'was never fitted'.
03 · Pressure control and safety systems 0/5
How many, what set pressure, and when were they last tested or replaced? One manufacturer publishes triple relief valves; a clinical maker publishes exact set pressures of 35.0 and 36.0 psig.
Walk away ifSet pressure unknown, or a valve has been adjusted by a previous owner.
Both should exist and should agree with each other. Check the glass, the needle at rest, and any calibration sticker.
Walk away ifGauges disagree, or the internal gauge is missing.
Can the occupant, and separately an attendant, depressurise quickly? A clinical benchmark is 30 psig to 0 in under 120 seconds, with an autonomous mode.
Walk away ifNo occupant-operable vent.
FDA's 2025 letter recommends ensuring proper grounding equipment is used, and notes wool and synthetics may generate more static than cotton. Electrostatic sparks have been identified as an ignition source in hyperbaric oxygen since 1966.
Walk away ifNo grounding provision on a chamber intended for oxygen-enriched use.
Two-way, powered, and audible at pressure. Test it at pressure, not on the bench.
Walk away ifNo working communication for a chamber that will be used with an occupant alone inside.
04 · Support equipment 0/5
Oil-free or oil-lubricated, hours run, filter change history, intake location. One manufacturer publishes 0.01 micron inline filtration; ask what is actually fitted now.
Walk away ifOil-lubricated compressor feeding breathing air with no documented separation.
Measure purity with a calibrated analyser at the flow you intend to run. Published purity falls at the top of the flow range on the units in the oxygen delivery table.
Walk away ifMeasured purity well below the manufacturer's published band and no service path.
Cracking, kinks, date codes, and thread condition. Oxygen-service fittings are not generic hardware.
FDA's 2025 letter directs users and facilities to follow the manufacturer's instructions. Without the manual you cannot claim to be doing that.
A materials study reported that elevated oxygen fraction and pressure increase flammability potential, and that all tested skin-care products ignited in 99.5% oxygen under pressure. Ask what the manufacturer permits inside.
05 · The occupant and the room 0/4
Measure bideltoid breadth and compare it to the chamber's internal diameter, not its external one. Several manufacturers, Prestige Hyperbaric among them, publish external dimensions only — in those cases ask the vendor to state the internal figure in writing rather than estimating it from the outside dimensions. See the sizing table on the specification reference page.
Reported middle-ear barotrauma incidence in published series ranges widely — 68.7% in one 1993 otoscopic-grading series of 67 users, 43.2% in a 236-user review, 262 of 2,610 in a five-year retrospective, 549 events over eight years in a 5,962-user review with therapy suspended for 89. It is the most common reported problem and it happens during compression.
Walk away ifAn intended user who cannot equalise and has no screening or stop procedure in place.
External footprint on the delivery path, ceiling height, floor loading for a hard shell of 800–2,100 lb, and a dedicated circuit if the manufacturer asks for one.
FDA's August 2025 recommendations include ensuring the patient is properly monitored and supervised for the duration of the treatment. Both 2025 flash-fire death reports under this product code describe unsupervised self-treatment.
Walk away ifA plan that depends on the occupant being sealed in alone with nobody present.
Sources for the claims above: FDA Letter to Health Care Providers, 25 Aug 2025 · FDA product classification (ASME PVHO-1, NFPA 99 recognised standards) · openFDA 510(k) records, product code CBF · openFDA MAUDE death reports, product code CBF · FDA Class 2 recall, determined cause “No Marketing Application” · barotrauma incidence figures from the evidence table.