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Estimating the Effects of EtO BIER-Vessel Operating Precision on D-Value Calculations D-values for several ranges of expected BIER-vessel performance have been calculated and compared with a common BI-certificate value. Commercially available biological indicators (BIs) are of critical importance to both the healthcare providers and device manufacturers that perform EtO sterilization. Because it is more easily controlled, radiation sterilization lends itself to parametric release based on chemical dosimeters. For steam sterilization, healthcare providers generally use commercially available BIs, but manufacturers of sterile products may take several other approaches to validation and routine release. Naturally occurring bioburden, BIs derived from resistant bioburden isolates, and commercially available BIs are commonly used for validation, while BIs or parametric release can be used for routine release. However, parametric release is not commonplace with EtO sterilization processes, and most routine release testing is performed with commercially available BIs. In addition, commercial BIs are used to establish microbial-lethality relationships in nearly all EtO process validations. When using BIs for these purposes, device manufacturers are dependent on the certifications performed by the BI manufacturers to assure that their products will meet the appropriate quality system regulation requirements. Such certifications are conducted in specialized test vessels known as biological indicator evaluator resistometers, or BIER vessels. The test requirements for BIs are specified by the , ISO standards, and European norms. Because the certifications are so important, some users attempt to verify the data presented in the certificate, but doing so can be challenging. Not only does verifying certificate values require hundreds of samples and a BIER vessel, but the performance of different BIER vessels is likely to vary, even though they are required to operate within the precise limits defined by the AAMI and ISO standards. Specifically, BIER vessels for EtO must comply with the following steady-state control limits: an