International standards recognize that electrical and electronic assemblies are subject to classification by intended end usage. Further, while the requirements of the IEC documents shall not constitute the sole cause of redesign or modification of a currently approved design or process, when existing assemblies undergo changes that affect hardware configurations, the design of the latter shall be reviewed and user-approved changes made that allow for maximum practical compliance. In addition, prior to commencing work, all instructors, operators and inspection personnel must be proficient in the tasks to be performed.