The principles of the flameproof protection concept are:
No external hot surfaces above temperature class.
Enclosure joints are designed with an MESG (Maximum experimental safe gap)
Non-metalic and cemented parts contributing to the flameproof properties of the enclosure undergo high temperature and humidity testing.
Parts fitted inside an enclosure may include sparking contacts, semi-conductor
devices and batteries.
Rotating parts (operating rods or motor shafts) can also be permitted, subject to design restraints.
Flexible enclosure walls or elements of enclosure walls are not permitted.