Flange:

Flange: Outer rim of an access door frame provided to
attach the frame to the duct.
HEPA: High Efficiency Particulate Air. To be called a
true HEPA filter, or certified HEPA filter the filter must
have a documented filtration efficiency of 99.97% at 0.3
micron-sized particles.
Highly Recommended: When the term highly
recommended is used in this document, it means the
practice or procedure is a component of the accepted
“standard of care” to be followed, though not mandatory
by regulatory requirement.