02 · Codes and standards
ASME PVHO-1 and PVHO-2
PVHO-1 governs how a pressure vessel for human occupancy is built and stamped. PVHO-2 governs what happens to it afterwards — and it contains most of the hard numeric intervals a chamber owner is actually accountable for.
PVHO-1
What the stamp certifies
The official scope of ASME PVHO-1, as published in FDA’s recognized consensus standards record, is that the standard “provides requirements for the design, fabrication, inspection, testing, marking, and stamping of pressure vessels for human occupancy, having an internal or external pressure differential exceeding 2 psi,” and also covers the design, fabrication, inspection, testing, cleaning and certification of PVHO piping systems. A PVHO is defined as a pressure vessel that encloses a human being within its pressure boundary under a differential exceeding 2 psi, and the standard names hyperbaric chambers, recompression chambers, decompression chambers, diving bells, submersibles and medical hyperbaric oxygenation facilities among the vessels it covers (FDA’s recognized standard record for PVHO-1-2023).
So the stamp is a statement about the vessel and its piping as built — design, fabrication, inspection, testing, marking and stamping. It is a new-construction standard: the window section of PVHO-1 applies to new construction only (ANSI preview of PVHO-2-2019). The current edition is PVHO-1-2023 (ASME’s PVHO-1 catalogue page).
NFPA 99, Chapter 14 is what points to PVHO-1: chambers must be designed, fabricated, tested and stamped in accordance with it, and viewports and penetrator plates in Class A and Class B chambers are designed and fabricated to it (UpCodes Chapter 14).
FDA lists both PVHO-1-2019 and PVHO-1-2023 as recognized consensus standards for hyperbaric chambers, alongside NFPA 99 editions (FDA product classification for hyperbaric chambers). FDA states it will accept declarations of conformity to PVHO-1-2019 until December 26, 2026, after which only PVHO-1-2023 declarations are accepted (FDA recognized standard record).
The full text of PVHO-1 is paywalled and was not read in preparing this page — only the official scope statement as published by FDA and the publisher’s catalogue record. The PVHO-2 intervals below come from the freely readable ANSI preview of the 2019 edition, Sections 1 and 2. The current edition is PVHO-2-2025 and was not read; verify every interval against the edition in force for your vessel before relying on it.
PVHO-2
In-service requirements
PVHO-2 is titled “Safety Standard for Pressure Vessels for Human Occupancy: Post-Construction Requirements,” and the current edition is PVHO-2-2025; prior editions are 2003, 2012, 2016 and 2019 (ASME’s PVHO-2 catalogue page). Its scope is the technical requirements and guidelines for the operation and maintenance of PVHOs designed, constructed, tested and certified to PVHO-1, plus the technical criteria that establish the serviceability of PVHO acrylic windows. Unlike PVHO-1’s window section, PVHO-2’s window provisions apply to all PVHO-1 acrylic windows regardless of date of manufacture (ANSI preview of PVHO-2-2019).
On jurisdiction, PVHO-2 states that operation is governed by the applicable jurisdiction, naming the state, the U.S. FDA and the U.S. Coast Guard as examples. On documentation, it requires an Owner’s Manual for each PVHO, a maintenance program supported by a maintenance manual, documented checklists, operating logs and maintenance logs, and a record of each pressurization cycle with maximum pressure or depth.
| Interval | Requirement |
|---|---|
| Every 12 months, ±30 days | Primary gauges indicating system and chamber pressures shall be deadweight tested or calibrated against a master reference gauge — or whenever a discrepancy greater than 2 percent of full scale appears between two equivalent gauges. |
| Before each pressurization | Viewports shall be visually inspected. If the PVHO is pressurised more than once per day, the inspection is required only before the first pressurization of that day. |
| 18 / 24 / 36 months | Maximum intervals for Maintenance Viewport Inspection, set by service environment and by whether service duration or cycles have passed design life. |
| After 18 months out of service | A Maintenance Viewport Inspection is required for windows out of service 18 months or longer, and also whenever a window is removed and reinstalled or a new window installed. |
| Every 10 years | Cylindrical-window chambers and marine intermittent-submersion service: completely refurbish viewports at 10-year intervals regardless of usage. Refurbishment requires complete removal of all viewport components. |
| Service environment | Within design life | Beyond design life |
|---|---|---|
| Protected | 36 months | 24 months |
| Typical | 24 months | 18 months |
| Severe | 18 months | 12 months |
All of the above from the ANSI free preview of PVHO-2-2019.
The interval that is not fixed
Periodic pressure testing is delegated, on purpose.
PVHO-2 makes the owner responsible for periodic pressure testing of the PVHO pressure boundary and systems, at test pressures at maximum operating pressure and not exceeding the maximum allowable working pressure. But the periodicity is “established by the user, manufacturer, and/or applicable jurisdiction” — the standard does not fix a numeric retest interval (ANSI preview of PVHO-2-2019).
That is worth stating plainly, because a retest interval is one of the most commonly asserted numbers in this industry. In the sources reviewed for this library, no commercial code fixes one for clinical hyperbaric chambers. The only concrete published figures found were in U.S. Navy guidance, which is not commercial code — see the maintenance intervals page.
Practically, that means your retest cadence has to be established from three inputs: your chamber manufacturer’s documentation, any state or provincial pressure-equipment authority with jurisdiction over the vessel, and your own written maintenance program. Some jurisdictions do regulate these vessels directly — Kentucky’s boiler and pressure vessel regulations define pressure vessels for human occupancy (Kentucky’s administrative regulations), and Ontario’s technical safety authority requires hyperbaric chamber design registration as PVHOs (TSSA in Ontario). Requirements are not uniform; verify yours.
Inspection roles
Who is allowed to inspect a window
PVHO-2 defines two minimum levels of viewport inspection — Operational Viewport Inspection and Maintenance Viewport Inspection — each performed by a qualified person, and two inspector qualification levels: Operational Inspector and Maintenance Inspector. The user is responsible for a written qualification procedure, and qualification records for third-party agents are retained for the term of employment plus three years (ANSI preview of PVHO-2-2019).
That is a documentation obligation as much as a technical one. If a contractor inspects your windows, you should be able to produce the written qualification basis for the person who did it.
Acrylic
Handling limits, service life, damage
- Temperature. Acrylic windows shall never be exposed to temperatures above 150°F (65°C). Cleaning uses warm water at or below 120°F (49°C) with an acceptable agent; hand cleaning and polishing only, because power tools require annealing. No radiation exposure above 4 Mrad.
- Storage. An unused acrylic window may be stored up to 10 years from fabrication without counting against service life, under stated conditions: at or below 125°F (52°C), no sunlight, no wetting and drying cycles, no harmful chemicals, stored flat and unstacked. Storage beyond 10 years counts day for day.
- Service life extension. In a protected environment, service life may be extended beyond design life on visual inspection alone, but no window may remain in service more than 10 years or 5,000 cycles beyond its design life unless tested per the standard’s test section — with cylindrical-window chambers allowed up to an additional 10,000 cycles maximum. In a severe environment, no extension is allowed on visual inspection alone. Each extension based on mechanical property testing is limited to 10 years, with an unlimited number of subsequent extensions. The standard also gives testing requirements for increasing the 40,000-hour design life.
- Damage classification. “Slight” damage means surface defects less than 0.02 in. (0.5 mm) deep, or edge chips less than 0.125 in. (3.175 mm) wide. Anything deeper or wider is severe damage requiring a PVHO-1-Qualified Window Fabricator. Field repair of slight damage may be done by hand sanding, starting at 240 grit and progressing finer, with no annealing or pressure test required.
All from the ANSI preview of PVHO-2-2019. A window near the edge of its service life, or with damage near the “slight” threshold, is a documentation decision as much as a technical one — and the wrong answer is expensive in both directions.
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
- ASME PVHO-1, Safety Standard for Pressure Vessels for Human Occupancyhttps://www.asme.org/codes-standards/find-codes-standards/safety-standard-for-pressure-vessels-for-human-occupancy
- ASME PVHO-2, Post-Construction Requirementshttps://www.asme.org/codes-standards/find-codes-standards/safety-standard-for-pressure-vessels-for-human-occupancy-in-service-guidelines
- ASME PVHO-2-2019 — free ANSI preview (Sections 1–2)https://webstore.ansi.org/preview-pages/asme/preview_pvho-2_2019.pdf
- 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
- 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
- Kentucky Administrative Regulations, Title 815 Ch. 15 Reg. 010 (PVHO definition)https://apps.legislature.ky.gov/law/kar/titles/815/015/010/
- TSSA (Ontario) — Keeping Hyperbaric Chambers Safe for Patientshttp://www.tssa.org/keeping-hyperbaric-chambers-safe-patients
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