前言隔爆外壳是防止由于电气设备内部产生的火花使易燃气体发生意外爆炸的手段之一。当平行法兰表面之间的间隙小于最大试验安全间隙（MESG）时，设备内部产生的爆炸就不能传播到外部。实际上，为了达到安全裕度，电气设备的法兰间隙小于最大试验安全间隙。曾有人认为，由于设 Foreword Flameproof enclosure is one of the means to prevent accidental explosion of flammable gas due to the spark generated inside the electrical equipment. When the clearance between the parallel flange surfaces is less than the maximum test clearance (MESG), the explosion inside the equipment can not propagate to the outside. In fact, to achieve safety margin, the flange clearance of electrical equipment is less than the maximum test safety clearance. Some people think that due to set