To test the performance of chemical and biological indicators, specific test equipment is required. BS EN ISO 18472 specifies the performance requirements for the test equipment to be used in order to establish the response of chemical and biological indicators to critical process variables. This standard does not apply to test equipment for irradiation indicators or low temperature steam and formaldehyde indicators.
Resistometers constitute test equipment designed to create precise and repeatable sterilizing environments, allowing the evaluation of their effect on biological inactivation kinetics, chemical reactions, material degradation and product bioburden. Resistometers allow precise variation of the environmental conditions and cycle sequences in order to produce controlled physical studies. When used with the defined test methods given in ISO 11138 for biological indicators and ISO 11140 for chemical indicators, the results of these studies can be used to demonstrate conformance of biological indicators and chemical indicators to these standards.
Resistometers differ from conventional sterilizers. Instrumentation selection and control requirements for resistometers are based upon mathematical models in which rates of reaction, measurement accuracy and process control requirements are evaluated to quantify the effects induced by test equipment-controlled variables. The requirements for accurate measurement, precise control, and rapid rates of change approach limits of commercially available process control and calibration instrumentation accuracy. The measurement and control requirements often prohibit practical validation of a resistometer using procedures that might be employed in a conventional heat or chemical sterilization system. Resistometers are considered test equipment rather than sterilizers; therefore, an understanding of instrumentation and process design is critical in clarifying requirements on precision and accuracy.
Practical design has to consider the following:
- achievable measurement and control
- acceptable equipment induced variation in test results
- economic design (utilizing tight process controls only where required)
- test method correlation with intended us
- historical knowledge applied to test procedures and an understanding of micro-environmental physical phenomena
- testing and analysis alternatives, when accurate quantitative determinations exceed physical measurement/control limits.
BS EN ISO 18472:2006 specifies the requirements for test equipment to be used to test chemical and biological indicators for steam, ethylene oxide, dry heat and vaporized hydrogen peroxide processes for conformity to the requirements given in ISO 11140-1 for chemical indicators, or the requirements given in the ISO 11138 series for biological indicators. This International Standard also provides informative methods useful in characterizing the performance of biological and chemical indicators for intended use and for routine quality control testing.
This International Standard does not address the methods used to demonstrate compliance of biological or chemical indicators to ISO 11138 and ISO 11140, as these are covered in the appropriate parts of these standards. Indicators used with combination processes, such as washer-disinfection, are not covered by this International Standard.
