The main issues of conventional explosion-proof enclosures for methane gas, which are mainly used in coal mines, are their high cost, the difficulty of visualization of a display device, and an inaudible sound of a speaker put in them.
In order to solve these issues, the authors fabricated three test vessels (8, 16 and 32 cubic cm), which have a clearance of 1.2 mm, a width of joint of 50 mm, and several total width of clearances. The materials used for fabricating them were thin steel and acryl resin plates. Methane gas explosion tests and tests for non-transmission of an internal ignition were conducted at a gas concentration of 9 and 7.5 vol. % using them. The test results revealed that all test vessels had an explosion-proof function similar to the conventional explosion-proof enclosure. In addition, it became clear that the maximum explosion pressures in the test vessels at 9 % were considerably low (about 5 to 130 kPa).
From the test results, it is judged that the test vessels have the potential for solving the issues mentioned above. Because we would be able to fabricate explosion-proof enclosures with lower resisting pressures and with a wider clearance when compared to the conventional ones, using inexpensive thin steel and transparent materials.