Blanson: Proud to certify to ASME PVHO-1 standards


Although pressure vessels have been used for many years across a diverse range of applications, it was not until their development for use in commercial diving, underwater caissons or construction that there was a necessity to satisfy requirements, rules and standards to enable them to be used safely and efficiently by humans.

Today such vessels are now referred to as Pressure Vessels for Human Occupancy (PVHO) and they and their acrylic (PMMA) windows are becoming even more widespread in marine transport, saturation diving, medical, and marine chambers as well as for pharmaceutical columns, tourist submarines, diving bells and ROV’s.

The first PVHO’s

Historically the use of PVHO’s dates as far back as the early 1600s but it wasn’t until 1830 when Lord Admiral Cochrane patented the use of compressed air in underwater chambers that the use of PVHO’s reached their prominence.

Prior to this such vessels were built to a set of rules put in place by the American Society for Mechanical Engineers (ASME) however, following experience the governing Section VIII rules were not enough to satisfy the guaranteed safety of humans occupying such vessels due to:

  • the variety of steels which were allowed under the code section
  • the consequences of colder weather on such materials
  • the unrecognised use of acrylic plastic for viewports (which then were made from tempered glass)

PVHO committee

In the 1970’s the American navy funded research into the testing of acrylic plastic for use in PVHO windows and view ports, noting that the failure of a viewport in a pressure vessel to perform, nearly always resulted in human casualties. This work was carried out by Jerry Stachiw, whose book “Handbook of Acrylics for Submersibles, Hyperbaric Chambers and Aquaria” is still today regarded as “The Bible of Acrylic.” His report was submitted to ASME with a request for the establishment of a clear safety standard highlighting the importance of the safety of viewports of PVHO’s.

As a result, the Codes and Standards board of ASME created a Committee on Pressure Vessels for Human Occupancy in 1971 as a subcommittee of ASME solely responsible for the standards to which pressure vessel viewports were designed, manufactured and implemented.

This led to the first PVHO safety standard, the AMSE PVHO-1 being issued in 1977.

This meant that any engineer undertaking the design or purchase of acrylic windows for PVHO’s must, prior to the commencement of any design, be informed about the new standard and ensure that all work adhered to, met and surpassed minimal operational requirements which include:

  • Material
  • Window Design
  • Manufacturing process
  • Mounting method

ASME PVHO-1-2012

Over the years, numerous standards have developed, with the current standard being that of the one above which provides the same requirements for all aspects of design, fabrication, testing and pressure resistance and is applicable to:

  • submersibles
  • hyperbaric chambers
  • high altitude or hypobaric chambers
  • medical oxygenation facilities
  • caissons
  • aerospace vehicles.
  • Marine/Sat Systems


Blanson: Proud to certify to ASME PVHO-1 standards

To date, the standard has maintained an exemplary safety record over 14.5 to 20,000 psi pressure ranges in hundreds of manned and unmanned applications which is why Blanson are proud to be fully accredited by DNV Germanischer Lloyd and adhere to the PVHO standards to ensure that all of our clients get the safest and highest quality precision cast and engineered acrylic windows and products.

Using our unique formula we have developed a grade of acrylic which is biocompatible and meets the requirements of both USP Class VI and Toxicity Compliance FDA 21 CFR 177.1010. This enables us in conjunction with the ASME PVHO-1 standard to pre certify our column tubes for use within a pressure vessel according to the requirements of ASME Boiler & Pressure Vessel Code for both the pharmaceutical and the food and drink industries. Our acrylic vessels carrying the ASME pre-certification will generally not require on-site pressure testing thus reducing cost and time in commissioning production plant.

To find out more, please browse our website or contact our specialist team of engineers today.