PVHOs
PVHOs are specialised vessels operating under pressurised conditions designed to accommodate human occupants. PVHOs typically operate using different pressurisation gas mixtures such as atmospheric air, Nitrox (approximately 64% nitrogen and 36% oxygen), Heliox ( approximately 80% helium and 20% oxygen).
Registration, Testing and Examination Requirements of PVHOs
PVHOs pressurised using compressed atmospheric air (including air mixtures within 10% variation from atmospheric air composition, where, for example, oxygen content varies from the standard 21% to between 19% and 23%) and being connected to an air compressing plant fall within the definition of air receivers under the Workplace Safety and Health Act (WSHA). Such PVHOs must comply with testing and examination requirements under regulation 27 and 31 of the Workplace Safety and Health (General Provisions) Regulations (WSH(GP) Regulations) and as well as other related provisions, if they meet the applicable registration thresholds.
PVHOs pressurised using gas mixtures, such as Nitrox (approximately 64% nitrogen and 36% oxygen) or Heliox (approximately 80% helium and 20% oxygen), do not fall within the definition of air receivers under the WSHA. However, such vessels must comply with the requirements under regulation 33 of the WSH (GP) Regulations as pressure vessels containing hazardous substances. Owners of such PVHOs will need to ensure that they are inspected by competent persons before use and are properly maintained in accordance with manufacturer specifications and applicable design standards. Owners have to implement effective control measures including proper maintenance procedures, safety systems, and ensuring relevant documentation including design calculations, material certificates, inspection reports, and maintenance records are kept up-to-date and available. Regardless of the composition of pressurisation gas, only an authorised examiner who is competent in the relevant PVHO design standard should be considered a competent person due to the specialised nature of these vessels involving human occupancy.
All PVHOs shall be designed to ASME PVHO-1 or BS PVHO standards. The use of alternative design codes requires approval from the Ministry of Manpower (MOM).