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In areas where there is a risk of explosive dusts or explosive gases and vapors, such as coal dust, flour, aluminum powder, hydrogen, etc., static electricity can cause fires or explosions, posing a great danger. Therefore, in explosive hazard areas, the use of insulating materials should be minimized. When selecting electrical insulating materials, it is advisable to aim for a minimum insulation resistance in order to prevent discharge when exposed non-metallic parts come into contact with live parts. For non-metallic insulating materials, the anti-static capability of a device can be evaluated by measuring the surface resistance of the device’s enclosure. https://pic2.zhimg.com/80/v2-4614be2efc53d174616005645273eccd_720w.jpg Surface resistance, measured in ohms (Ω), refers to the resistance between two electrodes in contact with the surface being measured. According to the requirements of the IEC60079 series of standards: 1. In Class II explosive gas environments, when the surface area of the non-metallic enclosure of electrical equipment exceeds a certain specified value (as shown in Table 1), it is necessary to test the surface resistance of this non-metallic material to ensure that, by selecting the appropriate material, the surface resistance meets at least one of the following requirements when measured in accordance with IEC 60079-0 26.13: (1) ≤1 GΩ at a relative humidity of (50±5)%; (2) ≤100 GΩ at a relative humidity of (30±5%). https://pic3.zhimg.com/80/v2-86b44e3604faac34ddec73d0d1ec2f3a_720w.jpg 2. In Class III explosive dust environments, if the surface area of the non-metallic casing of electrical equipment is no more than 500 mm2, the risk of static electricity need not be considered ； If this limit is exceeded, a test to verify the surface resistance is required. The judgment requirements are the same as those for the surface resistance test limits of Class II gas environments mentioned above. For fixed-installed equipment that cannot meet the surface resistance limits, it is possible to use a \"X\" added after the #explosion-proof# mark, along with appropriate warning labels on the equipment, and to inform the users in the instruction manual. Original article; copying and reprinting are strictly prohibited!