Testing for immunity to simultaneous disturbances and similar issues for risk managing EMC

Where electronic equipment must function so as to maintain very low risk levels for safety, financial, or other reasons, it is not sufficient to only test it for immunity to electromagnetic (EM) disturbances, whatever the test levels used. However, where EM immunity tests are used as a part of such equipment´s verification or validation, for their results to be meaningful for the achievement of low risks, it is necessary to increase the test levels significantly above the levels of EM disturbances that could occur in the operational environment(s). This paper describes a number of reasons for increasing immunity test levels, gives some guidance on by how much, and discusses the problems that this approach can encounter.