Basis of any (Ex) personnel competency training

Answer is simple: Conformity assessment – General requirements for bodies operating certification of persons (ISO/IEC 17024:2013)
Few days back on an event following topic has come up: where next on Ex personnel competency?
The ISO 17024 says as follows:
“This International Standard has been developed with the objective of achieving and promoting a globally accepted benchmark for organizations operating certification of persons. Certification for persons is one means of providing assurance that the certified person meets the requirements of the certification scheme. Confidence in the respective certification schemes for persons is achieved by means of a globally accepted process of assessment and periodic re-assessments of the competence of certified persons.
However, it is necessary to distinguish between situations where certification schemes for persons are justified and situations where other forms of qualification are more appropriate. The development of certification schemes for persons, in response to the ever increasing velocity of technological innovation and growing specialization of personnel, can compensate for variations in education and training and thus facilitate the global job market. Alternatives to certification can still be necessary in positions where public services, official or governmental operations are concerned.
In contrast to other types of conformity assessment bodies, such as management system certification bodies, one of the characteristic functions of the certification body for persons is to conduct an examination, which uses objective criteria to measure competence and scoring. While it is recognized that such an examination, if well planned and structured by the certification body for persons, can substantially serve to ensure impartiality of operations and reduce the risk of a conflict of interest, additional requirements have been included in this International Standard.
In either case, this International Standard can serve as the basis for the recognition of the certification bodies for persons and the certification schemes under which persons are certified, in order to facilitate their acceptance at the national and international levels. Only the harmonization of the system for developing and maintaining certification schemes for persons can establish the environment for mutual recognition and the global exchange of personnel.”
I would rather say the question in a different way: where back to the basics on Ex personnel competency? Direction towards the real content already defined by IEC standards.
It means any Ex personnel competency system may be ok, if the compliance to relevant IEC standards of the certification is proven based on ISO/IEC 17024:2013.