Glossary

Analog-to-digital conversion.
The process changes an analog signal into a digital value, representative of the magnitude of the signal at the moment of conversion.

A measure of sound pressure designed to reflect the response of the human ear, which does not respond equally to all frequencies. The ear is less efficient at low and high frequencies than at medium or speech-range frequencies. To describe sound in a manner representative of the human ear’s response, it is necessary to reduce the effects of the low and high frequencies with respect to the medium frequencies. The resultant sound level is said to be A-weighted, and the units are dBA. The A-weighted sound level is also called the "noise level". Sound level meters have an A-weighting network for measuring A-weighted sound levels. Most levels of occupational, industrial and environmental noise are measured using A-weighting.

A-weighting is the frequency sensitive corrections applied to linear sound level readings to approximate the way humans perceive sound.

The mass of water vapour per unit volume.
Also in H & V as humidity mixing ratio: mass of water vapour per unit mass of dry air.

The pressure above the absolute zero value of pressure that theoretically obtains in empty space or at the absolute zero of temperature as distinguished from gauge pressure (gage pressure).

The total force per unit area exerted by a fluid. It is the sum of atmospheric and gauge pressures.

Pressure referred to that of a perfect vacuum. It is the sum of gauge pressure and atmospheric pressure.

The temperature of air or gas measured from absolute zero. It is the Fahrenheit temperature plus 459.6 and is known as the Rankine temperature. In the metric system, the absolute temperature is the Centigrade temperature plus 273 and is known as the Kelvin temperature.

A quantity which expresses the ability of a ventilation system to reduce a pollution concentration relative to the feasible theoretical maximum performance.

The properties of a material composition to convert sound energy into heat, thereby reducing the amount of energy that can be reflected.

If a solid takes up a liquid or a gas, or a liquid takes up a gas and the latter permeates the former throughout its entire substance, absorption is said to take place.

Alternating current.

Ambient air in which there are no known contaminants at harmful concentrations and with which a substantial majority (usually 80%) of the people exposed do not express dissatisfaction.

The degree of precision. Usually expressed, in terms of error, as a percentage of the specified value, or as a percentage of a range.

Common indoor pollutant. Used as a solvent. Unsuited to tracer gas studies in occupied areas by reason of its odour and variable background concentration.

Actual cubic feet per minute.

Volume of gas flowing at existing temperature and pressure.

The American Conference of Governmental Industrial Hygienists.
Association which produces TLV (Threshold Limit Value) List, Industrial Ventilation Manual, Bioaerosol documents.

ACH is an acronym for Air Changes per Hour. It is a value representing the number of times each hour that an enclosure’s total volume of air is exchanged with fresh or filtered air.

The process of cleaning the interior surfaces of steam generating units by filling the unit with dilute acid accompanied by an inhibitor to prevent corrosion, and subsequently draining, washing and neutralizing the acid by a further wash of alkaline water.

Acidic components of gaseous emissions which are removed by wet or caustic scrubbing (e.g., SO2, HCl, HBr and HF). They may be recovered as products in a halogen acid furnace or neutralized with caustic.

Represents the amount of free carbon dioxide, mineral acids and salts (especially sulphates of iron and aluminium) which hydrolyse to give hydrogen ions in water and is reported as milli-equivalents per litre of acid, or ppm (parts per million) acidity as calcium carbonate, or pH (potential of hydrogen) the measure of hydrogen ions concentration.

Containing, producing, arising from, actuated by, related to, or associated with sound. The properties of a material that absorb or reflect sound.

Instrument for measuring gas concentrations by determining the speed of sound in the mixture.

A substance (or air gap) used to reduce the transmission of sound through walls, windows, etc.

A method of detecting cracks in a building where leakage may occur by placing a steady source of high pitched sound within the building and using a microphone outside as a detector. Leaks correspond to an increase in volume of the sound transmitted. This is a qualitative technique only.

A review of a space to determine the level or reverberation, or reflected sound, in the space (in seconds) as influenced by the building materials used to construct the space. Also, a study of the amount of acoustical absorption required to reduce reverberation and noise.

A professional, usually with an engineering degree, or certification (s) whom belongs to professional organizations, whose primary role is to provide advice on acoustical requirements and noise control in a variety of situations.

The acoustical characteristics of a space or room influenced by the amount of acoustical absorption, or lack of it, in the space.

The science of sound: its production, transmission and effects.

Term used by OSHA and NIOSH to express the level of toxicant which required medical surveillance, usually one half of the PEL (Permissible Exposure Limit).

Charcoal is an amorphous form of carbon formed by burning wood, nutshells, animal bones, and other carbonaceous materials. Charcoal becomes activated by heating it with steam to 800-900°C. During this treatment a porous, submicroscopic internal structure is formed which gives it an extensive internal surface area. Activated charcoal is commonly used as a gas or vapour adsorbent in air-purifying respirators and as a solid sorbent in air-sampling.

Flow rate of air at a certain point, at a certain condition at that point.

A controlled motor, relay or solenoid in which the electric energy is converted into a rotary, linear, or switching action. An actuator can effect a change in the controlled variable by operating the final control elements a number of times.

A device that creates mechanical motion by converting various forms of energy to rotating or linear mechanical energy.

Health effects which show up a short length of time after exposure.

Severe biological harm/death from a single or short term exposure to a toxin.

A substance so poisonous as to cause severe biological harm or death soon after a single exposure or dose.

Analog-to-digital converter.

The theoretical temperature that would be attained by the products of combustion provided the entire chemical energy of the fuel, the sensible heat content of the fuel and combustion above the datum temperature were transferred to the products of combustion. This assumes: No heat loss to surroundings and no dissociation.

The adiabatic heat gradient is, in Earth's atmosphere, the air temperature variation with altitude (i.e. the gradient of the temperature of air), which only depends on atmospheric pressure, that is to say without consideration of heat transfer with the environment and without consideration of condensation or precipitation.

The rate of decrease of temperature with increasing altitude in the atmosphere. If heat is neither gained nor lost from the air parcel under consideration, then the lapse rate is said to be adiabatic.

A thermodynamic process during which no heat is added to, or taken from, a substance or system.

The average of the air temperature (ta) and the mean radiant temperature (tr) at a given location. The adjusted dry bulb temperature (tadb) is approximately equivalent to operative temperature (to) at air motions less than 80 fpm (0.4 m/s) when tr is less than 120°F (50°C).

Methods of controlling employee exposure by job rotation, work assignment, or time periods away from the hazard.

Automatic Data Processing.

A material which has the ability to cause molecules of gases, liquids, or solids to adhere to its internal surfaces without changing the adsorbent physically or chemically. Certain solid materials, such as silica gel and activated alumina, have this property.

The adhesion in an extremely thin layer of molecules as of gases, solutes or liquids, to the surface of solid bodies or liquids with which they are in contact.

The interaction of a gas or vapour with a solid or liquid substrate.

The transport of a property by a fluid by embedding it in the main flow.

A structural material with good insulation properties.

Microorganisms that require the presence of oxygen.

A microorganism that can live and grow only where free oxygen is present.

A part or surface, such as a wing, propeller blade, or rudder, whose shape and orientation control stability, direction, lift, thrust, or propulsion.

A gaseous medium containing suspended particles.

A colloidal system in which the dispersal medium is a gas, and the disperse phase is finely divided solid or liquid particles with sizes from a few nm. to approx. 100 micron. The larger particles are lost rapidly by gravitational settling, the smaller particles are lost by coagulation.

The secondary combustion stage of some incinerators in which wastes are combusted, usually as liquids and gases, pyrolyzed constituents and unburned organics from a first stage with supplemental fuels added, if needed.

Automatic gain control.

Implies consolidation of solid particles into larger shapes by means of agitation alone, i.e., without application of mechanical pressure in moulds, or between rolls, or through dies. Industrial agglomeration usually is implemented in balling devices such as rotating discs, drums, or cones; but it can occur in a simple mixer. On occasion, however, the word agglomeration has been used to describe the entire field of particulate consolidation.

The change in the state of the fabric of a building with time.

Analog Input (also Artificial Intelligence).

American Industrial Hygiene Association.

The mixture of oxygen, nitrogen, and other gases, which with varying amounts of water vapour, forms the atmosphere of the earth.

The gaseous mixture (chiefly nitrogen and oxygen) of which the atmosphere is composed.

A burner for firing oil in which the oil is atomised by compressed air, which is forced into and through one or more streams of oil which results in the breaking of the oil into a fine spray.

An oil burner in which a stream of fuel oil is broken into very fine droplets through the action of compressed air.

A perforated block built into a wall to ventilate a room or the underside of a wooden floor.

A quantity of fresh air equal to the volume of the room (building) being ventilated.

The air change rate of a room is the ratio of the volumetric rate at which air enters (or leaves) a room divided by the volume of the room. Usually this is expressed in air changes per hour (ach).

A method of expressing the amount of air movement into or out of a building or room in terms of the number of building volumes or room volumes exchanged.

The gross movement of air between spaces in a building etc. (Particularly with respect to mechanical ventilation systems.)

A device used to remove airborne impurities such as dusts, gases, vapours, fumes, and smoke.

The artificial process of treating air to adjust and control its temperature, humidity, cleanliness and distribution simultaneously to meet the comfort requirements of the occupants of the conditioned space.

A piece of equipment for the treatment of air so as to control, simultaneously, its temperature, humidity, cleanliness and distribution to meet the requirements of a conditioned space.

Any moving stream of air.

A stream of air that creates a barrier between two spaces which are at different conditions. Used for fume cupboards, biological safety cabinets, department store doors.

Insufficient air in an air-fuel mixture to supply the oxygen required for complete oxidation of the fuel.

The density of air (air density) is the mass per unit volume of Earth's atmosphere, and is a useful value in aeronautics and other sciences. Air density decreases with increasing altitude, as does air pressure. It also decreases with increasing temperature or humidity. At sea level and 20 °C, air has a density of approximately 1.2 kg/m3.
At IUPAC standard temperature and pressure (0 °C and 100 kPa), dry air has a density of 1.2754kg/m3. At 20 °C and 101.325 kPa, dry air has a density of 1.2041 kg/m3. At 70 °F and 14.696 psia ( pound per square inch absolute), dry air has a density of 0.074887 lbm/ft3. (pound mass/cubic feet)

A circular, square, or rectangular air distribution outlet, generally located in the ceiling and comprised of deflecting members discharging supply air in various directions, and arranged to promote mixing of primary air with secondary room air.

The delivery of fresh or conditioned air to various spaces in a building, usually by mechanical means.

A sheet jet of air across an entrance, separating the air inside a building from the air outside. (Used to reduce the ingress of cold outdoor air or where there is heavy traffic through the entrance.)

An air passage, usually formed in sheet metal, plastics, etc. which may be of square, rectangular or circular cross section, used for guiding ventilation air to and from various parts of a building.

The pattern of air currents within a building.

(1) The volume rate of transport of air either within or through the walls of an enclosure.

(2) The mass rate of transport of air either within or through the walls of an enclosure.

A switch that incorporates a mechanism capable of detecting a flow of air. The mechanism operates the switch automatically at a preset airflow rate.

A small duct, built to withdraw bad air from a room.

The descriptive characteristic of a substance from which air has been removed.

The ratio of the weight or volume, of air to fuel.

Grating set into a wall to allow the free passage of air for ventilation, especially to the underside of floors.

The uncontrolled inward air leakage through cracks and interstices in any building element and around windows and doors of a building, caused by the pressure effects of the wind and/or the effect of differences in the indoor and outdoor air density, measured as an air change rate.

The leakage of air into a setting or duct.

Opening in an outside wall for the provision of fresh air
(1) for ventilation,
(2) for heating appliances and for combustion.

The uncontrolled flow of air through a component (duct, joint, coupling, window, building, ventilation system) mainly due to pressure difference.

An air inlet or extract device combined with a luminaire.

(1) An ancillary chamber giving access to an enclosure without changing the conditions in it and restricting leakage of air from or into the enclosure.

(2) Weather-stripping. (U.S.A)

The mathematical description of the movement and dispersion of airborne constituents (often used in risk assessment modelling).

The sampling for and measuring of pollutants in the atmosphere.

Air flowing out of a building through cracks and openings.

(1) An opening in a wall or shaft through which bad air is expelled to the outside.

(2) An opening through which fresh or conditioned air enters a room.

The passage of air through a component crack etc.

The contamination of air by noxious gases or dust particles.

The pressure exerted by the air. This may refer to static (atmospheric) pressure, or dynamic components of pressure arising from air flow, or both acting together.

(1) Impervious to air.

(2) Resistant to penetration by air.

Respirators that use filters or sorbents to remove harmful substances from the air.

Usually refers to the concentration in air of one or more pollutants. For more than one pollutant, air quality is expressed as a concentration over a certain period of time,. e.g. μg /m3 over 24 hours.

A passage, usually vertical, for admitting fresh air into a mine or a tunnel.

A shaft for ventilation.

(1) The gap between two panes in double glazed windows.

(2) The gap between two panels (or brick leaves) in hollow (cavity) wall construction.

The settling of air into layers of different density (temperature).

An air current, usually with well defined boundaries.

Respirator that provides a supply of breathable air from a clean source outside of the contaminated work area.

(1) Impervious to air.

(2) Resistant to penetration by air.

A general descriptive term for the leakage characteristics of a building.

Parameter describing the rate of movement of air.

Important when considering cooling effects and comfort criteria.

A purpose provided inlet.

A valved opening in the top of the highest drum of a boiler or pressure vessel for venting air.

A water spray system or device for cleaning, humidifying, or dehumidifying the air.

A suitable horn, bell, light or other device which when operated will give notice of malfunction or off normal condition

A minute fresh water plant growth which forms a scum on the surfaces of recirculated water apparatus, interfering with fluid flow and heat transfer.

Represents the amount of carbonates, bicarbonates, hydroxides and silicates or phosphates in the water and is reported as grains per gallon, or ppm as calcium carbonate.

A small electrically charged particle of very high velocity thrown off by many radioactive materials, including uranium and radium. It is made up of two neutrons and two protons. Its electric charge is positive.

The standard power supply available from electric utilities companies.

Amplitude modulation.

Surrounding, as the atmosphere, especially the outdoor environment.

The air that surrounds the equipment.

The standard ambient air for performance calculations is air at 80°F, 60% relative humidity, and a barometric pressure of 29.921 in. Hg, giving a specific humidity of 0.013 lb of water vapour per lb of dry air.

The air surrounding an object.

Temperature of the air, (1) outside the building, or (2) within a room.

The temperature of the air surrounding the equipment.

The temperature of the space (air) around the motor. Most motors are designed to operate in an ambient not to exceed 40°C (104°F).

The temperature of the gas around a test model, which is unaffected by the model's presence.

Common indoor pollutant arising from metabolic activity of occupants and from cleaning products. It has been used as a tracer gas in measurements of air change rates in large buildings. Measured by absorbing in dilute sulphuric acid, adding Nesslers Reagent and performing a colorimetric assay.
Advantages: Low concentrations, easy to produce.
Disadvantages: Small, high background in the domestic environment.

The standard unit of electric current. The current produced by a pressure of one volt in a circuit having a resistance of one ohm.

An organism that does not require molecular oxygen for growth.

Any bacteria that can survive in partial or complete absence of air.

Quantitative determination of the constituent parts.

An instrument for measuring the velocity of a fluid.

A device that measures the velocity of air. Common types include the swinging vane and the hot-wire anemometer.

A device used for measuring air or gas velocities.

(See flow meter, Cup anemometer, Drag anemometer, Hot Film Anemometer, Hot Grid Anemometer, Hot Wire Anemometer, Ionisation Anemometer, Laser Anemometer, Optical Anemometer, Propeller Anemometer, Pulsed Hot Wire Anemometer, Rotating Anemometer, Sinusoidally Heated Hot Wire Anemometer, Sonic Anemometer, Thermal Anemometer, Thermistor Anemometer, Vane Anemometer).

American National Standards Institute.

A particle which interacts with its counterpart of the same mass but opposite electric charge and magnetic properties (e.g., proton and antiproton), with complete annihilation of both and production of an equivalent amount of radiation energy. The positron and its antiparticle, the electron, annihilate each other upon interaction and produce gamma-rays.

Any device for treating gaseous emissions prior to discharge to the atmosphere by removing acidic gases, water vapour or particulates. Examples include baghouse, demister, ESP (electrostatic precipitator), IWS (ionizing wet scrubber), quench, scrubber and venturi.

Air quality standard.
Minimum statutory requirements for air quality with respect to contaminants. (e.g. oxygen/ carbon dioxide balance, formaldehyde, radon etc.)

Water limit temperature control, a safety device often used on boilers.

Pertaining to water.

One of the noble (or inert) gases: Atomic No. 18.
The radioactive isotope 41 Ar has been used as a tracer gas.
Radioactive argon is produced by neutron bombardment of stable 4O Ar.
Detector: Geiger counter, ratemeter or acoustic analyser.
Care must be taken during injection so that safe levels of radiation exposure are net exceeded. The short half- life is a disadvantage.

The rotating part of a brush type direct current (DC) motor. In an induction motor, the rotating part is called a rotor.

Applied to a group of hydro carbons and their derivatives characterized by presence of the benzene nucleus (molecular ring structure).

A filter's ability to remove a coarse dust particle.

(1) A device designed to keep sparks from escaping, as at a chimney opening.

(2) A device to impede the flow of large dust particles or sparks from a stack, usually screening at the top.

A sharp edge of a brick, of plaster or of other building elements.

American Standards Association. Has been renamed to ANSI.

Fibrous heat resistant minerals. Including :
(1) A fine fibrous amphibole. Forms include tremolite (Ca2.Mg5.Si8.022.(OH)2) and riebeckite (variety crocidolite) also known as blue asbestos (Na2.(Fe,Mg)5.Si8.022.(OH)2). This has fallen into disfavour due to the health hazard arising from the dust. It is known to be the most carcinogenic of the asbestos minerals.

(2) A fibrous serpentine (chrysotile) which is more common. (Mg3.Si2.05.(OH)4)

American Standard Code for Information Interchange.
Coding standard of characters in data processing.

Solid, non-combustible particulate residue usually comprised of a heavy, large-size fraction that settles by gravity (bottom ash), and a light, small-size fraction that is airborne (fly ash) and removed in APCDs.

The incombustible inorganic matter in the fuel.

A pit or hopper located below a furnace where refuse is accumulated and from which refuse is removed at intervals.

(1) A square hewn stone.
(2) Stone walls or facings finely dressed to given dimensions, laid in courses with thin joints.
(3) (USA) walling of burnt clay blocks larger than brick size (U.K. terra cotta) plus sometimes brickwork.

The American Society of Mechanical Engineers.

In air distribution outlets, the ratio of the length of the core opening of a grille, face, or register to the width. In rectangular ducts, the ratio of the width to the depth.

A burner in which the fuel in a gaseous or finely divided form is burned in suspension, the air for combustion being supplied by bringing into contact with the fuel, air drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream.

A burner in which combustion air at high velocity is drawn over an orifice, creating a negative static pressure and thereby sucking fuel into the stream of air; the mixture of air and fuel is conducted into a combustion chamber, where the fuel is burned in suspension.

These include everything of value that is owned, including tangible (physical) items, like cash, accounts receivable, inventory, land, buildings, equipment, etc., and intangible (non-physical) items, like trademarks, licences, and goodwill.

The process of dividing investments among different kinds of assets, such as stocks, bonds, real estate and cash, to optimise the risk/reward trade-off based on an individual's or specific situation and goals. A key concept in financial planning and money management.

The gaseous envelope which is held to the earth by gravitational attraction and which in large measure rotates with it.

(1) Pressure at ground level exerted by the column of atmosphere immediately above.
(2) or As (1) but referred to sea level.

The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 inches Hg, 14.7 psi, 407 inches w.g., or 760 mm Hg.

It is the pressure indicated by a barometer. Standard atmosphere is the pressure equivalent of 14.697 psi or 29.921 in. of mercury at 32°F.

The barometric reading of pressure exerted by the atmosphere. At sea level 14.7 lb per sq in. or 29.92 in. of mercury.

The force exerted on a unit area by the weight of the atmosphere.

A device by means of which a liquid is reduced to a very fine spray.

The sound reduction process in which sound energy is absorbed or diminished in intensity as the result of energy conversion from sound to motion or heat.

Sound containing frequency components lying between 20 and 20,000 Hz.

A chart or table relating hearing level for pure tones to frequency.

An instrument for measuring hearing acuity.

American Wire Gauge.

Consists of a propeller or disc type of wheel within a cylinder that discharges air parallel to the axis of the wheel.

Often called "endplay." The endwise movement of motor or gear shafts. Usually expressed in thousandths of an inch.