HEPA Air Filter Case Design and Installation

The HEPA air filter case is constructed of materials that correspond to the specific application, filtration requirements, and considerations of disposal ease and cost. Commonly used case materials include fire retardant plywood, chromized carbon steel, and alloys UNS S30400 and UNS S40900 stainless steels. The minimum thicknesses required to maintain rigidity under compressive loads ranging up to 1,400 pounds when the filter is clamped to a mounting frame, are 3/4 inch for wood and manufacturers standard steel sheet gauge for steel. Grade A-C, American Plywood Association (APA) PS-1 fire-retardant-treated plywood is acceptable, but the A face must be on the inside, facing the pack, and should be assembled with this face completely coated with a sealant to close off any leak paths.

The outer face should be filled and sanded as smooth as possible (for plywood). This is particularly important for industrial plant workers whose gloved fingers and hands must not be punctured by splinters from a wooden frame when replacing filters. For wooden case filters, case panels may be joined with riveted joints, which are assembled by gluing with an adhesive and double nailing or doubling screwing with coated box nails, corrosion-resistant plated screw nails, or flat-head wood screws. The end points of the fasteners must not penetrate the inside or outside surfaces of the case. Metal cases should be used in instances of potential wetting or high humidity at elevated temperatures and when the filter will be exposed to corrosive chemicals.