Abstract: A storage enclosure provided for storing containers of hazardous material with a secondary containment feature being provided by a one piece containment pan cradled within a support base frame work of support beams and side beams which also allow for visual inspection of the underside of the pan. The enclosure is of a very sturdy construction employing relatively heavy gauge steel sheets for side and rear wall panels mounted to panel supporting frames of tubular steel frame members. A pair of front doors are also made of steel panels secured to door frames of tubular steel construction. Footing channel members provide spaces for forklift mobility of the enclosure. The one piece panel roof and associated frame is secured by a friction fit to the enclosure side walls so that it may lift off when elevated internal pressures are experienced.