Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems

1.1
This part of the IEC 61508 series 
a) is intended to be used only after a thorough understanding of IEC 61508-1, which provides the overall framework for the achievement of functional safety
b) applies to any safety-related system, as defined by IEC 61508-1, that contains at least one electrical, electronic or programmable electronic element
c) applies to all elements within an E/E/PE safety-related system (including sensors, actuators and the operator interface)
d) specifies how to refine the E/E/PE system safety requirements specification, developed in accordance with IEC 61508-1 (comprising the E/E/PE system safety functions requirements specification and the E/E/PE system safety integrity requirements specification), into the E/E/PE system design requirements specification

e) specifies the requirements for activities that are to be applied during the design and manufacture of the E/E/PE safety-related systems (i.e. establishes the E/E/PE system safety lifecycle model) except software, which is dealt with in IEC 61508-3 (see Figures 2 to 4). These requirements include the application of techniques and measures that are graded against the safety integrity level, for the avoidance of, and control of, faults and failures

f) specifies the information necessary for carrying out the installation, commissioning and final safety validation of the E/E/PE safety-related systems

g) does not apply to the operation and maintenance phase of the E/E/PE safety-related systems - this is dealt with in IEC 61508-1 - however, IEC 61508-2 does provide requirements for the preparation of information and procedures needed by the user for the operation and maintenance of the E/E/PE safety-related systems; 

h) specifies requirements to be met by the organisation carrying out any modification of the E/E/PE safety-related systems

NOTE 1 This part of IEC 61508 is mainly directed at suppliers and/or in-company engineering departments, hence the inclusion of requirements for modification. 

NOTE 2 The relationship between IEC 61508-2 and IEC 61508-3 is illustrated in Figure 4. 

i) does not apply for medical equipment in compliance with the IEC 60601 series. 

1.2
IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are basic safety publications, although this status does not apply in the context of low complexity E/E/PE safety-related systems (see 3.4.3 of IEC 61508-4). As basic safety publications, they are intended for use by technical committees in the preparation of standards in accordance with the principles contained in IEC Guide 104 and ISO/IEC Guide 51. IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are also intended for use as stand-alone standards. The horizontal safety function of this international standard does not apply to medical equipment in compliance with the IEC 60601 series. 

1.3
One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. In this context, the requirements, test methods or test conditions of this basic safety publication will not apply unless specifically referred to or included in the publications prepared by those technical committees. 

NOTE The functional safety of an E/E/PE safety-related system can only be achieved when all related requirements are met. Therefore, it is important that all related requirements are carefully considered and adequately referenced. 

1.4
Figure 1 shows the overall framework of the IEC 61508 series and indicates the role that IEC 61508-2 plays in the achievement of functional safety for E/E/PE safety-related systems. Annex A of IEC 61508-6 describes the application of IEC 61508-2 and IEC 61508-3.