wall opening 14 through which access may be had to the interior of the enclosure 12 the opening 14 is of generally rectangular configuration elongated in a vertical direction and is defined by a door frame 16 provided in the upright wall 10 a door casing 18 is mounted on the door frame 16 a rectangular access door 20 overlaps the entire periphery of the casing 18 and is adapted to abut the casing 18 when the access door 20 is fully closed the door 20 is reinforced by cross stiffeners 19 affixed to the door side facing the interior of enclosure 12 grab bars 21 are mounted on the door frame 16 inside and outside of the enclosure 12 for ease of exit from and entry into the enclosure 12 a pair of spaced upper and lower parallel horizontal yokes 22 shown in fig2 5 and 6 span the access door 20 and the door casing 18 the yokes 22 are in the form of rigid channel members having a generally rectangular cross section and are bolted to corresponding brackets 24 which are in turn fixedly attached to the access door 20 one end of each of the yokes 22 is hingedly secured about a corresponding pivot pin 26 mounted on a pair of support brackets 28 connected to the door frame 16 thus the opening and closing of the access door 20 is readily effected through movement of the yokes 22 about the pivotal axis of pins 26 each of the yokes 22 is configured with a notch 29 at the other end as shown in fig6 in.