primarily for collecting particulate

NFPA: National Fire Protection Association.
Negative Air Machine: A HEPA-filtered air filtration
device designed primarily for collecting particulate and
limiting particulate migration while controlling workspace
pressure differentials. These machines may or may not
be ducted outside the building envelope.
Non-adhered Substance: Any material not intended or
designed to be present in an HVAC system, and which
can be removed by contact vacuuming.
Non-porous HVAC System Surface: Any surface of the
HVAC system in contact with the air stream that cannot
be penetrated by water or air, such as sheet metal,
aluminum foil, or polymetric film used to line flexible
duct.