Monthly Briefing September 2024

The Board received the response below relating to June’s Monthly Briefing.

‘Your briefing has many of us in the field asking, “What are the specific codes that are mandatory on a hard sided chamber used for human occupancy and pressurized above 1.4 ATM?” We are certainly aware of the ASME PVHO-1 for chambers and NFPA 99/101 for facilities. If a chamber has the ASME PVHO-1 stamp or placard on the chamber, is it considered safe for human occupants? Are there other stamps of approval that are necessary as well? Are these also affixed to the chambers themselves?  How does one tell if a new chamber has the right approvals? What is the FDA’s role if any, do they have an ID stamp?’

Chamber manufacturers in compliance with the ASME Boiler Pressure Vessel Code (BPVC) indicate this by stamping the letter ‘U’ onto each chamber’s ID plate. It sits within a clover leaf-like emblem and is commonly located on the upper left side. (See attached example)  The letter U indicates that it is an unfired pressure vessel, namely one not subjected to direct or indirect heat sources such as coal, gas or oil-fired boilers.

The U stamp will be accompanied by an ASME BPVC ‘National Board’ registration number also stamped onto the plate. (Same attached example) This number is specific to the chamber (its ‘birth certificate’), like an aircraft’s alpha numeric registration number painted on its fuselage, or an individual’s social security number. If, for example, an airline merges with another, aircraft tail numbers remain unchanged as they are specific to the aircraft not its owner. You may have seen the letters ‘US’ rather than ‘AA’ after the ID numbers on an American Airlines aircraft. This indicates it was once a part of the US Airways fleet before being acquired by American.

The National Board mandates that the manufacturer keeps a log of all their chambers registered with the NB, identifying NB registration number, issue date, authorized inspection agency acceptance date and manufacturer’s NB serial number. A manufacturer holding a U stamp is permitted to design, fabricate and test unfired pressure vessels/hyperbaric chambers. To retain this stamp, manufacturers must regularly update design and fabrication and are subject to routine inspections and examinations. So, NB compliance is an ongoing verification process. The U stamp and NB number represent evidence that all quality control system requirements laid out by the ASME BPVC have been met. The same cannot be said for chambers lacking NB identification.

With those stampings evident, one has every right to believe that the\a chamber is safe for human occupancy upon delivery. This is, however, just the first step – albeit a critical one – in terms of ongoing safety. The chamber must be maintained and serviced in accordance with the manufacturer’s instructions and operated consistent with good practice standards by those qualified to do so. This extends to adherence with respective NFPA dictates.

Evidence of compliance with the additional requirements of PVHO-1is less apparent as it does not feature on the chamber’s ID plate. A manufacturer may claim compliance while they are not because compliance is no longer based on third-party inspection. It has essentially evolved to one of self-certification. Tom Workman refers to this as a layered code. To claim PVHO-1 compliance first requires a chamber be compliant with ASME BPVC. It is worth noting that a chamber may be compliant with ASME BPVC but not with PVHO-1. One example wound be a chamber manufactured prior to 1977, the year the PVHO-1 standard came into being.

Neither the FDA nor NFPA play any role in chamber manufacture and design, so nothing relating to these organizations features on a hyperbaric chamber’s ID plate.

Dick Clarke, President

National Board of Diving & Hyperbaric Medical Technology