Monday, March 27, 2023

Glossary of Technical Terms

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.
Activated Carbon/Charcoal
A form of carbon capable of removing certain gases and odors from the air.
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.
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.
Airborne Particulate Cleanliness Classes
A set of particle concentration levels based upon the number of particles greater than or equal to specified sizes which are present in a unit volume of air.
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.
Aluminum Separator
Corrugated aluminum used to separate the folds of a pleated filter medium and provide air channels between them.
Ambient Air
Refers to untreated air existing in any location.
Airborne Molecular Contamination
An instrument for measuring the force or speed of air.
American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc. The organization which historically set standards for low and medium efficiency air filters.
Plate or vane used to direct or control movement of air within a confined area.
A fan used to move air under pressure.
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.
Refers to a level of cleanliness in a cleanroom as measured by particles per cubic feet per minute.
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.
Any unwanted substance present in or on a material or any surface within a clean zone.
To reduce the level of a clean zone or material by the addition of contaminants.
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.
An operable device used to control supply pressure or flow by varying the air path area, usually in a duct.
Delta P
See: Pressure Drop
Differential Pressure
See: Pressure Drop
See: Air Diffuser
The most general term to define the scattering of particulate matter suspended in air or other gases.
The removal of unwanted substances from personnel, rooms, building surfaces, equipment, etc.
Dioctyl Phthalate, an aerosol medium used as a challenge for efficiency and leak testing of HEPA filters.
Round or rectangular conduit through which air is carried from a central air conditioning system to various locations in a building.
An aerosol of particles of any solid material, usually with particulate size of less than 100 microns.
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.
A screen affixed to the face of a filter unit to protect it against damage caused by mishandling.
A device used for moving or producing artificial currents of air.
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.
Feet per Minute
Gasket (Filter)
Material used to prevent air leakage between the filter frame and its holding device.
High Efficiency Particulate Air. Also see: Filter, High Efficiency Particulate Air.
Housing (Filter)
A device used to hold a filter.
Institute of Environmental Sciences and Technology. The organization which historically sets standards for high efficiency air filters.
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 airstream lines because of its inertia. Instead it moves in a straight line colliding with the filter fiber or surface to which it may become attached.
Inches of Water Gauge (WG)
A unit of measuring pressure or pressure differential (1 in. WG = 0.036 psi).
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
See: Unidirectional Airflow
Magnehelic® Gauge
Registered trade name for a diaphragm activated dial gauge that measures changes in air pressure. These readings can translate into several measurements that include filter resistance, air velocity, fan and blower pressures, and furnace draft.
Make-up air
Unfiltered air that is introduced into a re-circulated air system.
An instrument for measuring pressure of gases and vapors. Gas pressure is balanced against a column of liquid in a U-shaped tube.
The filtering material in a filter (plural: media).
(µm, often abbreviated as um, micron or µ) A unit of measurement of length, equal to one-millionth of a meter (approximately 0.00003937 inch).
Micron (µm)
See: Micrometer

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.
The passive liberation of a gas from any material.
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.
An adjective referring to particles, e.g., particulate matter.
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%).
See: Aerosol Photometer
An enclosure in which air or other gas is at a pressure greater than that outside the enclosure.
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.
Pressure, Total
The sum of static pressure and velocity pressure at the point of measurement.
Pressure, Velocity
The impact pressure associated with the velocity of a flowing fluid. It is related to the kinetic energy per unit volume of the flow.
PSL (Polystyrene Latex Spheres)
Uniformly sized latex particles used as a challenge agent in some filter tests when suspended in an aerosol.
Recommended Practice
A published document that provides technical guidance, philosophy or preferred procedures regarding a given topic.
Resistance (Filter)
See: Pressure Drop
Roughing Filter
A prefilter with high efficiency for large particles and fibers but low efficiency for small particles, usually of the panel type.
A method for disclosing leaks in filter units in which the probe nozzle of an aerosol photometer is held approximately one inch from the area to be tested and moved at a rate of not more than 10 ft/min (3 m/min) across the test area. Also known as probing.
Specification - Design
A concise document that provides the requirements for a product's construction and performance.
Standard Air
Air at 50% relative humidity, with a temperature of 21ºC (69.8ºF) and pressure of 760 mm Hg (29.92 in Hg.).
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.
Ultra Low Penetration Air 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.
The distance traveled in a given time. Air velocity is measured in feet per minute (FPM) or meters per second (m/s).
Water Gauge (WG)
A means of designating pressure or differential pressure in terms of the height of an equivalent column of water, commonly expressed as inches WG in the English system (1 inch = 0.036psi).
Work Zone
The space or volume within the cleanroom that is designated for contamination-controlled operations, and for which cleanliness testing is required.