IES: Institute of Enviromental Sciences. A professional organization dedicated to the promotion of technology in several different areas. The Contamination Control Division of the Association has written several Recommended Practices for HEPA and associated filters and equipment.

Impingement: The process in which particles are removed from an airstream because of their inertia. As air containing a particle, flows toward a filter fibre or other collecting surface, the particle does not follow the air streamlines because of its inertia. Instead it moves in a straight line colliding with the filter fibre or surface to which it may become attached.

Inches of Water Gage (in \. w.g.): A unit used in measuring pressures. The equivalent measurent in SI is Pascals. 1 in. w.g.= 0.036 psi = 248.8 Pascals (Pa).

Inertia: The tendency of a body in motion to move in the same straight line unless acted upon by some external force.

Infiltration: The controlled or uncontrolled leakage of air into a conditioned space.

Inorganic: Molecules whose chemical structure do not contain carbon.

Interception: The process in which a particle is removed from an airstream as it follows the streamilnes around a fiber. The particle comes in contact with a fiber and stays attached to it because the attractive forces between the fibre and the particle are stronger than the forces of disruption of the moving airstream.

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