The equipment to work on these types of atmospheres are grouped by :
1) Devices Group I : To work in the mines or outdoor installations where explosive atmospheres may occur .
a. Category M 1: very high level of protection .
b . Category M2 : high level of protection
2) Devices Group II : Intended for use in other locations may be danger of formation of explosive atmospheres .
a. Category 1: very high protection level . Although failing a means of protection, there is another still retaining the level of protection .
b . Category 2: High level of protection.
c . Category 3: normal level of protection.
Electrical equipment suitable for explosive areas
Electrical equipment is only suitable for explosive areas , if constructed in accordance with one of the following modes of protection:
◦ d = proof envelope . Electrical equipment is enclosed inside an envelope capable of withstanding the explosion and not transmit inflammation in the surrounding environment or by their boards of union , or other communications.
= ◦i increased safety . Ensure it is based on formation of arcs , sparks or overheating in devices , taking : a high safety factor , inaflojables special terminals , high quality insulation with a minimum IP54 .
◦ i = intrinsic safety . A device or circuit is intrinsically safe when it is not able to produce enough sparks or thermal effects caused by the inflammation of a particular gas atmosphere . Instrumentation is indicated , as is designing low voltage circuits and reduce the intensity taking also into consideration the possible defects that may occur and the storage of energy in capacitors, inductors and cables .
◦ p = internal pressure . The machines are fitted with electrical equipment or an envelope or installed in a room where it prevents the entry of flammable vapors or gases , maintaining the interior air or non-flammable gas at a pressure greater than atmospheric outside.
◦ = oil immersion . It is done so that it can ignite flammable gases or vapors that are above the level of oil and the outside of the envelope .
◦ q = powdered insulation . Parts under voltage electrical equipment are fully submerged in a mass of powdered insulation .
◦ m = encapsulation . The elements are enclosed in a protecting resin , so that an explosive atmosphere can not be ignited by sparks or or contact hot parts internal to the package .
