Research on safe power threshold of radio wave explosion-proof in coal mine

In order to prevent gas explosion caused by radio waves emitted by wireless equipment in the coal mine, the power and energy of radio waves in coal mines should be limited. This paper introduces the safety power threshold of continuous radio wave explosion-proof specified in different standards. ① GB/T 3836.1-2021 Explosive atmospheres-Part 1: Equipment-General requirements and the international standard IEC 60079-0:2017 Explosive atmospheres-Part 0: Equipment-General requirements refer to the European standard CLC/TR 50427:2004 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation-Guide. When there is no slender structure object (such as a crane) that can be used as a receiving antenna in an explosive environment, the clause that the explosion-proof safety power threshold of continuous radio wave in Class I environment (representative gas is methane) is 8 W is omitted. It is indiscriminately stipulated that the safe power threshold of continuous radio wave explosion-proof in Class I environment is 6 W. ② The British Standard BS 6656:1991 Guide to prevention of inadvertent ignition of flammable atmospheres by radio-frequency radiation specifies that for continuous radio-wave operating frequencies greater than 30 MHz in a Class I environment, the safe power threshold for continuous radio-wave explosion-proof is 8 W, Whether there is a crane or other slender annular structure object. ③ The British Standard BS 6656:2002 Assessment of inadvertent ignition of flammable atmospheres by radio-frequency radiation - Guide and the European Standard CLC/TR 50427:2004 both specify a safety power threshold of 8 W for continuous radio-wave explosion-proof in Class I environments without slender annular structures such as cranes. The safe power threshold of continuous radio wave explosion-proof in Class I environment with slender annular structures such as cranes is 6 W. The characteristic of the underground environment and equipment in the coal mine are analyzed. Generally, there is no crane underground. The underground coal mine is a confined space, with a long roadway but a small roadway section. Cable, water pipe, rail, steel wire rope, overhead line, tape rack and other axial conductors laid along the roadway axis are thin and long, but will not form a ring antenna conducive to radio wave reception. Transverse conductors such as roadway I-beam support can form a ring antenna conducive to radio wave reception. However, the section of the I-steel conductor is large, which does not meet the characteristics of slender structure. The hydraulic support in the fully mechanized working face can form an annular structure. However, the hydraulic support jack divides it into multiple annular structures. The support conductor section is large, which does not meet the characteristics of slender structure. It is pointed out that before the explosion-proof safety power threshold of continuous radio wave in coal mine is implemented to 6 W, the mine wireless communication systems such as leakage, induction, through-the-ground and multi-base stations have been widely used in the coal mine. And there is no case of gas and coal dust explosion accident. Therefore, the threshold of explosion-proof safety power of radio wave in the coal mine is set as 6 W without distinction, which lacks of theoretical analysis and experimental verification. In particular, 5G, WiFi 6, UWB, ZigBee and other mining mobile communication systems and personnel and vehicle positioning system working frequency is higher. Therefore, the coal mine continuous radio wave explosion-proof safety power threshold should be 8 W.