This International Standard gives a number of optimized test plans@ the corresponding operating characteristic curves and expected test times. In addition the algorithms for designing test plans using a spreadsheet program are also given@ together with guidance on how to choose test plans. This standard specifies procedures to test whether an observed value of ?C failure rate@ ?C failure intensity@ ?C mean time to failure (MTTF)@ ?C mean operating time between failures (MTBF)@ conforms to a given requirement. It is assumed@ except where otherwise stated@ that during the accumulated test time@ the times to failure or the operating times between failures are independent and identically exponentially distributed. This assumption implies that the failure rate or failure intensity is constant. Four types of test plans are described as follows: ?C truncated sequential tests; ?C time/failure terminated tests; ?C fixed calendar time terminated tests without replacement; ?C combined test plans. This standard does not cover guidance on how to plan@ perform@ analyse and report a test. This information can be found in IEC 60300-3-5. This standard does not describe test conditions. This information can be found in IEC 60605-2 and in IEC 60300-3-5.