inside the enclosure to travel outside the enclosure to potentially ignite or cause a blow out disaster on the drilling rig or site after explosion proof enclosure encountering an explosion event the explosion proof enclosure 10 must be replaced or the expandable wall member 70 may be replaced the flat portion of the wail member 70 may be attached to the next similarly constructed wall thus creating the form of the enclosure preferably the front and back sides are generally flat to provide a surface for a window indicators and or inlets outlets the wave length and amplitude may be selected from the deformation properties of the material and the size e g volume shape etc of the enclosure 10 the size of the enclosure is the maximum volume of potentially explosive mixture contained within the first enclosure volume 30 at the time of explosion the determination is based on the most expansive or extensive explosion that the explosion proof enclosure may be subjected to be encountered at site the wave length extendibility expandability is the full length of the waif l p u00d7 d u00d7 n where the full length l is the length of the wall d is the length of wave p u00d7 d is the length of one wave and n is the number of waves the extendibility expandability length is the volume of the cone extended to the cone perimeter equal to le l u2212 lw where le is the extendibility of the wall in linear units the calculations may be performed by one skilled in the art for various explosive substances 50.