HEPA filters are recognized as one of the finest forms of mechanical air filtration available
for this application. HEPA filters improve or become more efficient as they load under use.
There are a number of mechanisms involved in HEPA filtration which are briefly presented
below:
1. Impingement - Large particulates, e.g. dust, are captured by the filter fibers as the
air stream flows around the fibers.
2. Interception - Particulates follow air stream around filter fibers and become
captured (physical interference between particles and fibers).
3. Diffusion - Very small “particles” are bombarded by gas molecules causing them
to move erratically (Brownian motion) and contact the filter fibers.
4. Straining - Occurs when the smallest dimension of the particulate is greater than the
distance between adjoining filter media fibers.
5. Electrostatic attraction - Enhances mechanical capture through attraction of
oppositely charged particles.
Unidirectional (Laminar) Air Flow
The Laminar Flow Glovebox /Isolator offers the highest level of product protection by
providing vertical laminar flow HEPA filtered air to the complete work environment. This
is the same technology used in the Laminar Flow Workstations and Biological Safety
Cabinets that “barrier isolators” are intended to replace. The Laminar Flow Glovebox
/Isolator utilizes a full width and depth supply HEPA filter above the work surface. Any
particle-laden air is swept from the work area with a wash of HEPA filtered air. Filtered air
washes over the work area into the front and rear grilles. Particles that are generated by the
work are immediately washed into the returns and out of the work zone. Internal cross-
contamination from compounding different products in the same work area is drastically
reduced.
The Laminar Flow Glovebox /Isolator can be configured for either positive or negative
pressure operation. When the system is operating under positive pressure it is referred to as
an Isolator and when operating under negative pressure it is referred to as a Glovebox.
• Negative pressure Glovebox operation should be used when personnel protection
has been determined to be of greater concern.
• Positive Pressure Isolator operation should be used when product protection has
been determined to be of greater concern.
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