III. Classification of equipment according to equipment protection levels
1.   According to the likelihood of becoming a source of ignition and conditions of its use in explosive atmospheres equipment is classified to equipment protection levels:
1)   «ultra explosion-proof» («very high»);
2)   «explosion-proof» («high»);
3)   «equipment protection by increased safety» («increase safety») .
2.   Ultra explosion-proof («very high») equipment protection level is applied to equipment intended for use in accordance with the operational parameters specified by the manufacturer, ensures the required equipment protection level even in the event of rare failures relating to equipment, with an explosive atmosphere present, and which in the event of failure of one means of protection, at least an independent second means provides the required level of protection or the required level of protection is assured in the event of two failures occurring independently of each other;
Equipment with this equipment protection level is intended for use in underground mines and surface installations of such mines suseptabel to firedamp and/or combustible dust (group I equipment) or at the objects and/or its parts (group II and II equipment) where explosive atmosphere, created by the mixture with air of flammable substances in the form of gas, vapour, dust, fibres, or flyings is present permanently for long-term periods or frequently.
3. Explosion-proof («very high») equipment protection level is applied to the equipment intended for use in accordance with the operational parameters specified by the manufacturer, ensures the required equipment protection level and functioning under normal operation mode in the event of single recognized expected fault.
Group I equipment with this equipment protection level shall be provided with the means of safe shutdown when the specified concentration of the firedamp in the surrounding atmosphere achieves.
Equipment with this equipment protection level is intended for use in underground mines and surface installations of such mines endangered by the possible presence of firedamp and/or combustible dust (group I equipment) or at the objects and/or its parts (group II and III equipment) where explosive atmosphere is likely to present in the form of gas, vapour, dust, fibres, or flyings.

4.             Equipment protection level  «equipment protection by increased safety» («increased safety») is applied to equipment intended for use in accordance with the operational parameters specified by the manufacturer and which ensures functioning only in normal operation mode specified by the manufacturer.
Group I equipment with this equipment protection level shall be provided with the means of safe shutdown when the specified concentration of the firedamp in the surrounding atmosphere achieves.
Equipment with this equipment protection level is intended for use in underground mines and surface installations of such mines (group I equipment) where firedamp and/or combustible dust or explosive atmosphere created by the mixture with air in the form of gas, vapour, dust, fibres, or flyings is not likely to occur in normal operation, but if it does occur, will persist for a short period only.