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Chem-Zone
TM
Directly Exhausted Work Zone
Unique to the Axiom is the Chem-Zone, a directly exhausted work zone. The central
portion of the work surface is surrounded by grilles on the sides, front and back. Air
entering these grilles is drawn to the Exhaust HEPA filter, and when the cabinet is in B-
mode and connected to an exhaust system, out of the laboratory. This feature prevents
the recirculation of volatile chemicals as seen in Type A cabinets, while exhausting
much less air than Type B2 models. This is illustrated in Figure 5-3.
HEPA Filters
HEPA filters are disposable, dry-type particulate filters. The filter material or media is
typically made of borosilicate microfibers formed into a thin sheet, in a process similar to
the production of paper. This sheet is folded, or pleated to increase its surface area.
The pleats are typically held in place by beads of glue that add rigidity to the media
pack. The pack is then set into a frame, and sealed as shown in Figure 5-4.
The HEPA filter manufacturer establishes the efficiency of the filter by challenging it with
an aerosol of known particle size. The number of particles that penetrate the filter are
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