Airguard Microguard 99 H1123B33-0AG000000 HEPA Filter, 11-3/8 x 23-3/8 x 11-1/2 in, 500 CFM

Airguard Microguard 99 HEPA filter, part number H1123B33-0AG000000, a deep-pleat high efficiency particulate air filter in a galvanized steel cell measuring a nominal 11-3/8 x 23-3/8 x 11-1/2 inches and labeled for 500 CFM. Airguard was a CLARCOR company, and the Microguard 99 line continues under Parker Hannifin.

Microguard 99 filters are built from a continuous sheet of microglass media pleated around corrugated aluminum separators and sealed into the frame so air cannot bypass the pack. Each filter is tested at the factory, which is why the label carries handwritten penetration and resistance readings with a tested stamp. The series is offered at 99.97, 99.99 and 99.999 percent efficiency on 0.3 micron particles.

These filters serve as final filters in cleanrooms, pharmaceutical and food processing rooms, hospital isolation and laboratory exhaust, and in air handlers and fan filter housings where cross-contamination must be controlled. The half-size 11-3/8 x 23-3/8 face fits housings built for half-module HEPA filters. The label is UL Classified Class 1 for flammability.

Available from King Surplus inventory in Del Rio, Texas.

• Manufacturer: Airguard, a CLARCOR company (Louisville, KY), as labeled; the Microguard 99 line is now sold under Parker Hannifin
• Product: Microguard 99 standard capacity HEPA filter
• Part Number: H1123B33-0AG000000 (label)
• Label Codes: 138224-001-0803-0002 and 2971101
• Nominal Size (label): 11-3/8 x 23-3/8 x 11-1/2 in
• Rated Airflow (label): 500 CFM
• Factory Test Record: % penetration and resistance (in. W.G.) are handwritten on the label and stamped tested; the handwritten values are not legible in the photos and are not stated here
• Airflow Direction: marked by arrow on the label
• Construction (series): pleated microglass media with corrugated aluminum separators in a galvanized steel cell, fully sealed media pack, 11.5 in depth available
• Efficiency (series): HEPA grades of 99.97%, 99.99% and 99.999% at 0.3 micron; the grade of this unit is not legible on the label
• Maximum Operating Temperature (series): 180 F (82 C)
• Agency: UL Classified air filter unit as to flammability only, Class 1, 453N (label)
• Spec Basis: Airguard and UL labels read directly from KSC record 18468 gallery photos 2026-09-16; Parker MICROGUARD 99 Standard Capacity HEPA Filter specification (parker.com) and Micro Guard 99 HEPA and ULPA Filters bulletin (filterprocess.com).