This Standard provides technical criteria and guidelines for the operation and maintenance of PVHOs and PVHO systems that were designed, constructed, tested and certified in accordance with ASME PVHO-1. (b) This Standard provides technical criteria for the user to establish the serviceability of a PVHO acrylic window under its specific environmental service conditions. Windows in protected environments as well as those in severe environments are addressed. Judicious use of this Standard will allow the user and/or the jurisdictional authority to determine when a PVHO acrylic window requires replacement.