IV. Types of protection of equipment
1. Depending on the special measures applied to prevent ignition of the surrounding explosive atmosphere one type or combination of several types of explosion protection may be applied to:
1)           electrical equipment intended for use in explosive gas atmospheres:
"d" – flameproof enclosure;
"е" – increased safety;
"i" ("ia", "ib", "ic") – intrinsic safety (intrinsically safe electric circuit);
"m" ("mа", "mb", "mс") –encapsulation by compound;
"nА" – non-sparking equipment;
"nС" - enclosed-break devices, hermetically-sealed device or non-incendive components producing arcs, sparks or hot surfaces;
"nR" - restricted-breathing enclosure;
"nL" - energy-limited apparatus;
"nZ" – pressurized enclosure;
"о" - oil immersion;
"р" ("рх", "ру", "pz") - pressurization;
"q" - powder filling;
"s" - special protection;
2)           electrical equipment intended for use in explosive dust atmospheres:
"t" ("ta", "tb", "tc") – protection by enclosure;
"i" ("ia", "ib") - intrinsic safety (intrinsically safe electric circuit);
"m" ("ma", "mb", "mc") - encapsulation;
"p" - pressurization;
"s" - special protection;
3)            non-electrical equipment intended for use in explosive atmospheres:
"с" – protection by constructional safety;
"b" - protection by control of ignition source;
"k" – protection by liquid immersion;
"d" – protection by flameproof enclosure;
"fr" - Protection by flow restricting enclosure;
"р" - pressurization;
4)          other recognized types of explosion protection.
2. The types of explosion protection of equipment are determined by the following special measures, applied to equipment with different levels of protection to avoid ignition of a surrounding explosive atmosphere:
1)    flameproof enclosure "d" - type of protection in which the parts capable of igniting an explosive gas atmosphere are provided with an enclosure which can withstand the pressure developed during an internal explosion of an explosive mixture, and which prevents the transmission of the explosion to the explosive gas atmosphere;
2)    dust ignition protection type «t» - type of protection whereby all equipment is protected by an enclosure to avoid ingress of dust and by means of surface temperature limitation;
3)    increased safety "е"  -  type of protection in which additional measures are applied so as to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks in normal service or under specified (abnormal) conditions;