all which meet the requirements of the partners. like IEC (and similar) standards say: proof of evidence shall be delivered that one is competent.
it means at the enduser side there is a need of policy: what level Ex personnel competency is a minimum to have.
one interesting standard to here: ISO 17024 – https://www.iso.org/standard/52993.html – it says: ISO/IEC 17024:2012 contains principles and requirements for a body certifying persons against specific requirements, and includes the development and maintenance of a certification scheme for persons. SO proof of evidence shall be delivered based on ISO 17024.
and another one: PT 60079-44 – explosive atmospheres – personal competence – To develop a document identifying the minimum level of knowledge and skills required to work in hazardous areas and the specific competence required for work associated with equipment for explosive atmospheres.
keep up good work!