This part of IEC 61508 provides information on – the underlying concepts of risk and the relationship of risk to safety integrity (see Annex A); – a number of methods that will enable the safety integrity levels for the E/E/PE safety-related systems to be determined (see Annexes B, C, D and E). The method selected will depend upon the application sector and the specific circumstances under consideration. Annexes C, D, E, F and G illustrate quantitative and qualitative approaches and have been simplified in order to illustrate the underlying principles. These annexes have been included to illustrate the general principles of a number of methods but do not provide a definitive account. Those intending to apply the methods indicated in these annexes should consult the source material referenced.