Gas Group
MESG
Maximum Experimental Safe Gap (MESG)
Definition: (Ref: IEC 60079-1 ) Maximum Experimental Safe Gap (for an explosive mixture ) of a joint 25mm in width which prevents any transmission of an explosion during 10 tests made under the conditions specified in IEC 60079-1-1
Gas Group – IIA
Gas Group – IIB
Gas Group – IIC
Gas Group
MIC (Minimum Ignition Current) Ratio is
The minimum current required from an inductive spark discharge to ignite the MOST EASILY IGNITABLE MIXTURE of a GAS, MIST or DUST in air
For the assessment of the ignition of gases and vapours in a circuit using a equipment defined EN IEC 60079-11, a comparative value with methane as reference in a standardised circuit is used. This comparative value is the minimum ignition current ratio, MIC. It is the means used for classifying gases and vapours within explosion group II in the subgroups IIA, IIB and IIC.
An Inductor stores energy in its Magnetic Field. An energized inductive circuit, if interrupted (by opening a switch or accidentally cutting the connecting wire) then this current, which is flowing in the circuit will ultimately become ZERO in a very short time. This rate of change of current will develop a voltage across the point of interruption. A large inductive effect can generate high voltage. This voltage will cause a spark across the point of interruption..
Gases and vapours may be classified according to the ratio of their minimum igniting currents (MIC) with the ignition current of laboratory methane. The standard method of determining MIC ratios shall be with the apparatus described in IEC 60079-11.
Group II equipment is subdivided and, for the purpose of classification of gases and vapors. MIC ration are :
Group IIA: MIC > 0,8.
Group IIB: 0,45 ≤ MIC ≤ 0,8.
Group IIC: MIC < 0,45.