Explosion protection

EXPLOSION PROTECTION (EN: explosion protection; DE: Explosionsschutz; FR: protection contre l'explosion; ES: proteccion contra la explosion; RU: взрывозащита) is the complex of the means for the ensuring of the normal operation of the equipment within the places, which are dangerous because of the explosion of the gas or dust (the mine workings of the underground mines, the beneficiation plants, and others). The electric devices, which are provided with the explosion protection, are named the explosion-protected electric equipment.

Depending on the field of the usage, they distinguish within the USSR the following explosion-protected electric equipment: group I, the ore-mining equipment, which is purposed for the usage within the underground workings of the mines and ore mines, which are dangerous because of the gas (methane) or coal dust; group II, for the indoor and outdoor installation within the places, which are dangerous because of the gases, vapours, and dust.

The marking signs for the explosion-protected electric equipment are: P for the group I, Ex for the group II. Within the USSR, they distinguish the following types of the explosion protection: the protection of the e type, the explosion-proof shell, the spark-safe electric circuit, the filling of the shell with oil, the filling of the shell with quartz, the filling or blowing of the shell with the air under the excessive pressure, the automatic shutdown, and the special type of the explosion protection. The protection of the e type within the electric equipment, which does not have the normally sparking parts, is ensured using the means and technical solutions, which are preventing the limiting heating of the equipment, the emergence of the electric sparks and arcs, which are able to cause the ignition of the combustible gases and vapours. This protection is achieved with the usage of the electric insulating materials of the high quality, with the increasing of the electric gaps, with the increasing of the reliability for the connection of the electricity conducting parts, with the decreasing of the temperature of the heating, and so on.

For the marking of the explosion-protected electric equipment, where is used this type of the explosion protection, there is used the sign II (the electric equipment of the group I), and also the sign e (the equipment of the group II). In case of the usage of the explosion-proof shells (the major type of the explosion protection for the power electric equipment), the necessary effect is achieved with the usage of the so-called flange or labyrinth protection within the places of the connection of the parts, on the account of the imparting the necessary strength to the shell. In case of the explosion of the gas inside the shell as the result of the sparking or short circuit, there emerge no dangerous damages of the shell; the explosion does not propagate into the environment.

The marking signs for the explosion-proof shell for the explosion-protected electric equipment of the group I (depending on the supplied voltage, and on the current of the short circuit) are 1B, 2B, 3B, 4B; of the group II (depending on the category of the medium, which is dangerous because of the explosion) are IIA, IIB, and IIC. The spark-safe electric circuit is created in such a manner, that the electric discharge or heating do not cause the ignition of the medium, which is dangerous because of the explosion. The spark-safety of the circuits is ensured on the account of the limiting for the magnitudes of the voltage and electric current, on the account of the shunting of the inductive elements, and so on. This type of the explosion protection is sub-divided into the three sub-groups.

The signs for the marking (in the ascending order for the level of the explosion protection) are: for the explosion-protected electric equipment of the group I - IIc, IIb, IIa; of the group II - Ic, Ib, Ia. The filling of the shell with the oil is used for the prevention of the ignition of the combustible gases or vapours, which are surrounding the shell, in case of the emergence of the spark, electric arc, or in case of the increasing of the temperature of the electric elements inside this shell. The marking signs for this type of the explosion protection are: for the electric equipment of the group I - M; of the group II - O. The quartz filling for the shell (the sign for the marking is K), and the creation of the inert gas environment within this shell, or the blowing of this shell with the clean air (the sign for the marking is P), serve the same goals, as the filling with the oil. The automatic shutdown of the circuit comprises the withholding of the voltage from the electric ity conducting parts (in case of the destruction of their protective shell) during the time, which is excluding the ignition of the environment, which is dangerous because of the explosion (the sign for the marking is A). Sometimes the explosion protection is ensured using the special means, the protective action of which is based on the principles, which differ from the principles, which are listed above. The marking for the special type of the explosion protection is the sign C.

Depending on the level of the explosion protection, they distinguish the electric equipment: with the increased reliability against the explosion, explosion-protected, and especially explosion-protected. The increased reliability of the explosion-protected electric equipment against the explosion is ensured mostly with the usage of the explosion protection of the type e; the explosion-protected level is ensured with the usage of the explosion-proof shells, of the spark-safe electric circuits of the corresponding sub-group, with the filling of the shell with the oil and quartz, with the blowing of this shell with the air under the excessive pressure, with the automatic shutdown, with the usage of the special type of the explosion protection; the especially explosion-protected level is ensured with the usage of the spark-safe electric circuits, or of the special type of the explosion protection. They distinguish the temperature classes for the explosion-protected electric equipment, which are determining the limiting temperatures of the heating for the external surfaces of these devices, which are established in accordance with the temperature of the spontaneous ignition for the gases and vapours, for the contact with which this equipment is calculated. The marking signs for the level of the explosion protection (in the ascending order) for the groups I, II, respectively, are RP, RV, RO; 2Ex, 1Ex, 0Ex; the signs for the temperature classes are T1, T2, T3, T4, T5, T6.

The marking of the explosion-protected electric equipment is performed according to this sequence: the signs for the level of the explosion protection, and for the belonging to one group or another group; the signs for the types of the explosion protection; the temperature class (only for the electric equipment of the group II).

The requirements and norms for the structure, and for the methods for the testing of the explosion-protected electric equipment within the USSR, have been published within the corresponding GOST governmental standards; abroad, such requirements are published within the national standards. There are acting the Interelectro CMEA international recommendations and standards for the explosion-protected electric equipment.