1.1 This part of ISO 11140 specifies general requirements and test methods for indicators that show exposure to sterilization processes by means of physical and/or chemical change of substances, and which are used to monitor the attainment of one or more of the variables required for a sterilization process. They are not dependent for their action on the presence or absence of a living organism. NOTE Biological test systems are regarded as those tests which are dependent for their interpretation on the demonstration of the viability of an organism. Test systems of this type are considered in the ISO 11138 series for biological indicators (BIs). 1.2 The requirements and test methods of this part of ISO 11140 apply to all indicators specified in subsequent parts of ISO 11140, unless the requirement is modified or added to by a subsequent part, in which case the requirement of that particular part will apply. Relevant test equipment is described in ISO 18472. NOTE Additional requirements for specific test indicators (Class 2 indicators) are given in ISO 11140-3, ISO 11140-4 and ISO 11140-5.