Glossary of Terms

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Activated Carbon / Charcoal – A form of carbon ´activated´ by treatment with oxygen to have very high surface area, capable of removing many gases and odors from the air.
Aerosol – An assemblage of small particles, solid or liquid, approximately 100µ or smaller in size. Example: dust, smoke, fog.
Aerosol Photometer – A device used to determine particle size and distribution in air by measuring the mass concentration of scattered light.
Aerosol Spectrometer – A device used to determine particle size and distribution in air by measuring the range of color produced by passing a white light through a prism.
Air – The mixture of gases that make up the atmosphere; ~78% nitrogen, ~21% oxygen with the balance consisting of smaller amounts of gases including argon, carbon dioxide, neon, helium, and other gases.
Air Change – A measure of the amount of air moving in or out of a space because of leakage or mechanical ventilation. One air change is a volumetric flow of air equal to the cubic content of the space.
Air Cleaner – A device used for the removal of particulate or gaseous impurities from the air.
Air Diffuser – An air distribution outlet designed to direct airflow into desired patterns.
Air Filter – A device for removing particulate material from an air stream.
Ambient Air – Refers to untreated air existing in any location.
ASHRAE – American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc. The organization which historically set standards for low and medium efficiency air filters.

Baffle – Plate or vane used to direct or control movement of air within a confined area.
Bacterial Filtration Efficiency (BFE) – is a test is performed on filtration materials and devices such as face masks, surgical gowns, caps, and air filters, which are designed to provide protection against biological aerosols. The test determines the filtration efficiency of these materials when challenged with a biological aerosol of Staphylococcus aureus. The BFE test procedure is based on Military Specification 36954C and can evaluate filtration efficiencies up to 99.9%. This test is required by the ASTM F2100 and EN 14683, as well as used for 510K submissions to the FDA.
Blower – A fan used to move air under pressure.

CFM – Cubic Feet per Minute
Challenge Concentration – The concentration of an aerosol of known character used to test a filter, under specified conditions, for the purpose of determining efficiency and/or leakage.
Cleanroom – A room (facility) in which the air supply, air distribution, filtration of air supply, materials of construction, and operating procedures are regulated to control airborne particle concentrations to meet appropriate cleanliness levels.
Clean Work Station – A clean-air device such as a bench or similar enclosure, characterized by having its own supply of filtered air.
Clean Zone (Area) – A defined space in which the concentration of airborne particles is controlled to specified limits.
Contaminant – Any unwanted substance present in or on a material or any surface within a clean zone.
Contaminate – To reduce the level of a clean zone or material by the addition of contaminants.
Contamination – The result of the addition of contaminants to a material or any surface within a clean zone.
Contamination Control – Any organized effort taken to reduce the level of contamination.
Controlled Environment – An environment in which parameters such as temperature, pressure, humidity, contaminant level and so forth are controlled within specified limits.

Damper – An operable device used to control supply pressure or flow by varying the air path area, usually in a duct.
Delta P – A change in Pressure – also see Pressure Drop
Differential Pressure – A Pressure gradient – also see Pressure Drop
Diffusers – A device that distributes a subject (air) evenly – also see Air Diffuser
Dispersion – The most general term to define the scattering of particulate matter suspended in air or other gases.
Decontamination – The removal of unwanted substances from personnel, rooms, building surfaces, equipment, etc.
DOP – Dioctylphthalate, an aerosol medium used as a challenge for efficiency and leak testing of HEPA filters.
Duct – Round or rectangular conduit through which air is carried from a central air conditioning system to various locations in a building.
Dust – An aerosol of particles of any solid material, usually with particulate size of less than 100 microns.
Efficiency – The ability of a device to remove particulate or gaseous material from an airstream by measuring the concentration of the material upstream and downstream of the device.

Filter, High Efficiency Particulate Air (HEPA) – A throwaway, extended-medium, dry-type filter in a rigid frame, having a minimum particle-collection efficiency of 99.97% (that is, a maximum particle penetration of 0.03%) for 0.3µm particles of thermally generated DOP or specified alternative aerosol.

Filter, Ultra Low Penetration Air (ULPA) – A throwaway, extended-medium, dry-type filter in a rigid frame, having a minimum particle-collection efficiency of 99.999% (that is, a maximum particle penetration of 0.001%) for particles in the size range of 0.01 to 0.02µm, when tested in accordance with the methods of IES-RP-CC007.
FPM – Feet per Minute

HEPA – High Efficiency Particulate Air. See also Filter, High Efficiency Particulate Air.
Housing, Filter – A device used to hold a filter.

Impingement – The process in which particles are removed from an airstream because of their inertia. As air containing a particle flows toward a filter fiber or other collecting surface, the particle does not follow the airstreamlines because of its inertia. Instead it moves in a straight line colliding with the filter fiber or surface to which it may become attached.
Interception – The process in which a particle is removed from an airstream as it follows the streamlines around a filter. The particle comes in contact with a fiber and stays attached to it because the attractive forces between the fiber and the particle are stronger than the forces of disruption of the moving airstream.

Laminar Flow – Air that flows in a single pass, in a single direction, with uniform velocity through a cleanroom or clean zone with generally parallel streamline. See also Unidirectional Airflow

Make-Up Air – Unfiltered air that is introduced into a re-circulated air system.
Manometer – An instrument for measuring pressure of gases and vapors. Gas pressure is balanced against a column of liquid in a U-shaped tube
Medium – The filtering material in a filter (plural: media).
Micron (µm) – (micrometer often abbreviated as um, micron or µ) A unit of measurement of length, equal to one-millionth of a meter (approximately 0.00003937 inch).
Mini-Environment – An environment that provides localized control of airborne contaminants by means of an enclosure designed to isolate product-handling areas from personnel and the surrounding room environment.
Most Penetrating Particle Size (MPPS) – The size of the particles that achieve maximum penetration of the filter medium. Particles that are smaller or larger than the most penetrating size exhibit a lower rate of penetration; the reduced penetration of the smaller particles is due to diffusion mechanisms, while for the large particles it is due to interception and inertial effects. The most penetrating size is a function of the structure of the filter medium, the velocity of the airflow through the filter, and the physical and chemical nature of the particles.
O-Probe – A method used to test HEPA and ULPA filters for leaks utilizing either an aerosol photometer or discrete-particle counter. A sampling probe is moved in a series of parallel, slightly overlapping strokes across the test area at a distance of approximately 2.5cm (1 inch) from the filter face.

Particle – An object that is solid, liquid or both, usually between 1 nanometer and 1 millimeter in size.
Particle Concentration – The number of particles per unit volume of air.
Particle Count – The number of particles detected (or reported) in a given volume of air.
Particle Counter, Airborne – An instrument for continuous counting of airborne particles larger than a given threshold size. The sensing means may be optical, electrical, aerodynamic, etc.
Particle Counter, Optical – A light scattering instrument with display and/or recording means to count and size discrete particles in air.
Particle Size – The apparent maximum linear dimension of a particle in the plane of observation, as observed with an optical microscope, or the equivalent diameter of a particle detected by automatic instrumentation. The equivalent diameter is the diameter of a reference sphere having known properties and producing the same response in the sensing instrument as the particle being measured.
Particulate – An adjective referring to particles, e.g., particulate matter.
Penetration – The exit concentration of a given particulate or gas from an air cleaning device, expressed as percentage of inlet concentration, i.e. 99.99% efficiency = .010% penetration (100% – 99.99% = .010%).
Photometer – an instrument used to measure light intensity, also see Aerosol Photometer
Plenum – An enclosure in which air or other gas is at a pressure greater than that outside the enclosure.
Prefilter – A filter unit installed to protect a second filter from high dust concentration or other environmental conditions. The prefilter usually has a lower efficiency than the filter it protects.
Pressure Drop (Differential) – Also referred to as resistance, the difference of the air pressure entering the filter and the air pressure exiting the filter at a stated flow and under given conditions. The pressure drop of a filter is a measure of its resistance to airflow through it. Typically expressed in inches of water column (gauge) or in Pascals.
Pressure, Gauge – The amount by which the total absolute pressure exceeds the ambient atmospheric pressure.

Resistance (Filter) – See: Pressure Drop

Specification, Design – A concise document that provides the requirements for a product´s construction and performance.
Standard Air Density – Air having a density of approximately 1.201 Kg/m³ (0.075 lb/ft³); that is, standard air with a specific volume of 0.832 m³/kg (13.33 ft ³/lb).
Static Pressure – The potential pressure exerted in all directions by a fluid. For a fluid in motion it is measured in the direction normal to the direction of flow.

ULPA – Ultra Low Penetration Air, also see Filter, Ultra Low Penetration Air
Ultrafine Particles – Particles in the size range from approximately 0.02µm to the upper limit of detectability of the discrete particle counter.
Unidirectional Airflow – Air that flows in a single pass, in a single direction, with uniform velocity through a cleanroom or clean zone with generally parallel streamlines. Formerly referred to as Laminar Flow.
Uniform Airflow – Unidirectional airflow pattern in which the point-to-point readings are within plus or minus 20% of the average airflow velocity for the total area of the laminar flow work zone.

Velocity – The distance traveled in a given time. Air velocity is measured in feet per minute (FPM) or meters per second (m/s).

Water Gauge (w.g.) – A means of designating pressure or differential pressure in terms of the height of an equivalent column of water, commonly expressed as inches w.g. in the English system (1 inch = 0.036psi).