The European Standard IEC 60079 which covers Electrical Apparatus for Explosive Gas Atmospheres passed into statute law in 2003. Compliance with this is mandatory. In answer to the various opinions stated on this forum BS 60079-17:2003 which covers the Inspection and Maintenance of Electrical Equipment in Hazardous Areas states in
4.2 Qualifications of personnel
The inspection and maintenance of installations shall be carried out only by experienced personnel, whose training has included instruction on the various types of protection and installation practices, the relevant rules and regulations and on the general principles of area classification. Appropriate continuing education or training shall be undertaken by personnel on a regular basis. Evidence of the relevant experience and training claimed shall be available.
The equipment that falls under this standard must have ATEX Certification for use within the European Community. Compex is a company that supplies training covering BS 60079, hence the name Compex Trained. Hope this helps.