Glossary of Terms

Don’t get lost in the technical terms. We break down the scientific lingo and provide straightforward context about indoor environmental hazards and solutions. 

Acceptable Indoor Air Quality – air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction.

Aerosol Sample – a predetermined measured volume of air is drawn across sample media and is then sent to an appropriate laboratory for analysis.

Air Conditioning – control of temperature, moisture content (humidity), circulation, and purity of the air within a space to produce the desired effects on the occupants of that space or products and material manufactured or stored there.

Air Exchange Rate – the number of times that the outdoor air replaces the volume of air in a building per unit of time, typically expressed as air changes per hour; or the number of times that the ventilation system replaces the air within a room or area within a building.

Analyte – substance or material being sampled and analyzed.

Bacteria – microscopic organisms living in soil, water, organic matter, or the bodies of plants and animals; characterized by lack of a distinct nucleus and lack of ability to photosynthesize.

Biological Contaminants – agents derived from or that are living organisms that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases.

Biohazard Cabinetry – designed to minimize hazards inherent in work with biohazards; there are three classes of cabinetry designed for work with the four levels of biohazards; also called Biological Safety Cabinets

Biohazards – infectious agents, or part thereof, presenting a real or potential risk to the well-being of man, animals, and/or plants directly through infection or indirectly through disruption of the environment.

Biosafety Level 1 – work is performed with defined and characterized strains of viable microorganisms not known to cause disease in healthy adult humans; representative microorganisms include Bacillus subtilis and canine hepatitis.

Biosafety Level 2 – work is performed with the broad spectrum of indigenous moderate-risk agents present in the community and associated with human disease in varying severity; primary hazards to personnel working with the agents may include accidental autoinoculation, ingestion and skin or mucous membrane exposure; representative microorganisms include Hepatitis B virus and salmonellae.

Biosafety Level 3 – work is performed on indigenous or exotic agents where the potential for infection by aerosols is real and the disease may have serious or lethal consequences; representative microorganisms include Mycobacterium tuberculosis and Coxiella burnetiid.

Biosafety Level 4 – work is performed on dangerous and exotic agents, which pose a high individual risk of life-threatening disease; representative microorganisms include the Lassa fever virus.

Building Envelope – all external building materials, windows, and walls that enclose the internal space.

Building Related Illness – diagnosable illness whose symptoms can be identified and whose cause can be identified and whose cause can be directly attributed to airborne building pollutants.

Bulk Sample – a predetermined area is removed from the material of interest (wallboard, carpet, insulation, water, etc.) using instruments sterilized in isopropyl alcohol, when appropriate, wearing gloves, and then placed in the appropriate container and shipped to the laboratory for analysis.

Building Diagnostics – as defined by the Building Research Board, consists of a four-step procedure:  1) knowing and determining what to measure, 2) using appropriate instrumentation, 3) interpreting the results and 4) predicting likely outcomes.

Chemical Fume Hood – localized exhaust, kept under negative pressure, designed to capture, and exhaust gaseous chemical contaminants to the outdoors.

Chromatography – a technique in which molecules in a mobile phase are separated because of their different affinities for a stationary phase; the greater the affinity for the stationary phase, the longer the molecule is retained.

Class I Biohazard Cabinetry – ventilated cabinet for personnel and environmental protection, with an uncirculated inward airflow away from the operator; suitable for work with biosafety levels 1, 2, or 3 where product protection is not required.

Class II Biohazard Cabinetry – ventilated cabinet for personnel, product, and environmental protection having an open from with inward airflow for personnel protection, downward HEPA-filtered laminar flow airflow for product protection and HEPA-filtered exhausted air for environmental protection; suitable for work with agents assigned to biosafety levels 1, 2 or 3; four distinct types of Class II cabinets are covered under NSF International Standard 49

Class III Biohazard Cabinetry – totally enclosed, ventilated cabinet of gas-tight construction; operations in the cabinet are conducted through attached rubber gloves while the cabinet is maintained under negative pressure; suitable for work with biosafety levels 1, 2, 3, or 4.

Comfort – condition of mind that expresses satisfaction with the environment; comfort can be related to thermal conditions, perceivable odors, relative humidity, and other environmental conditions.

Critical Temperature – temperature above which a gas cannot be liquefied, regardless of the amount of pressure applied.

Dust – air suspension of particles (aerosol) of any solid material; usually with particle size less than 100 micrometers.

Electronic Air Cleaner – imposes a charge on transient dust particles then sets up an electrostatic field to attract the charged particles to oppositely charged parallel collector plates.

Electrostatic Air Filter – a mechanical filter whose collection efficiency is augmented by an electrostatic charge other than a continuous external power source on the media; the electrostatic charge may be imposed at the time the media is manufactured or it may be generated by the flow of dry air through the media.

Electron Microscope – class of microscope that uses electrons rather than visible light to produce magnified images of objects; linear magnification up to or exceeding one million.

Environmental Factors – conditions other than indoor contaminants that cause stress, comfort, and/or health problems.

Ergonomic Stressor – conditions occurring in the workplace that could cause stress to the occupants (workers); examples can include atmosphere, environmental factors, heat, light, sound, equipment, and/or health problems.

Flame Ionization Detection – (FID) gas chromatograph detector in which solute (a minor component of the solution) is burned in a hydrogen-oxygen flame to produce CHOions; the current carried through the flame by these ions is proportional to the concentration of susceptible species in the eluate (what comes out of the chromatography column).

Fumes – airborne particles, usually less than 1 micrometer in size, formed by condensation of vapors, sublimation, distillation, calcination, or chemical reaction.

Fungi – any of a major group of lower plants that lack chlorophyll and live on dead or other living organisms; can include molds, rusts, mildews, smuts, and mushrooms.

Gas – state of matter in which substances exist in the form of nonaggregated molecules, and which, within acceptable limits of accuracy, satisfies the ideal gas laws, usually a highly superheated vapor.

Gas Chromatography – (GC) form of chromatography in which the mobile phase is a gas.

High-Performance Liquid Chromatography – (HPLC) chromatographic technique using very small stationary-phase particles and high pressure to force solvent through the column.

Human Commensal Bacteria – bacteria associated with humans.

Humidity – water vapor within a space.

Absolute Humidity – weight of water vapor per unit space.
Relative Humidity – humidity in one space is compared to humidity in another space; ratio of the quantity of water vapor in air to the quantity that would saturate that specific area at any given temperature.

Infiltration – air leakage inward through cracks and interstices and ceilings, floors, and walls of a space or building.

Laminar Flow Hood – clean bench, clean workstation, wall or ceiling-hung module, or other device (except a clean room) that incorporates a HEPA/ULPA filter(s) and motor-blower to supply laminar flow clean air to a controlled workspace.

Legionella Bacteria – bacteria that causes Legionnaires’ disease and Pontiac Fever; grows in water; water found in many systems such as cooling towers, evaporative condensers, and humidifiers can serve as amplifiers.

Light Microscope – class of microscope using visible light to produce magnified images.

Mass Spectrometry – (MS) apparatus in which a sample is bombarded with electrons to produce charged molecular fragments that are then separated according to their mass in a magnetic field.

Microscopy – investigation using a microscope.

Moisture – Relative Humidity – the ratio of the partial pressure of the water vapor in the air to the saturation pressure of water vapor at the same temperature; ideal parameters for relative humidity found in indoor office environments should be between 30 & 60%; relative humidity less than 30% can contribute to dry skin, eye irritation, and respiratory discomfort; relative humidity levels greater than 60% can contribute to increased chances of microbiological growth and other moisture-related phenomena.

Negative Pressure – a condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas; air flows into negatively pressurized spaces form positively pressurized areas.

Observational Investigations – designed to relate occupant response, possible sources, and building systems; usually includes an executive session to outline specific analysis requirements.

Odor – a quality of gases, liquids, or particles that stimulates the olfactory organ; occasionally odors are detected by humans at quantities too low to be analytically quantified.

Ozone – O3, trivalent oxygen; a rather toxic gas and very powerful oxidizing agent formed from molecular oxygen (O2) either photochemically or by subjecting O2 to an electrical discharge; primary uses of ozone are to purify drinking water, to deodorize air and sewage gases and to bleach waxes, oils, and textiles.

Oxidizing Agent – takes (accepts) electrons from another element in the compound causing the element to lose electrons to be oxidized.

Ozone Generator – a device (sold as an air purifier) that produces ozone (an EPA-regulated air contaminant); most generators lack a definitive metering device resulting in ozone being introduced at unknown concentrations indoors.

Particulate Matter – state of matter in which solid or liquid substances exist in the form of aggregated molecules or particles; airborne particulate matter is typically in the size range of 0.01 to 100 micrometers.

Positive Pressure – condition that exists when more air is supplied to a space than is exhausted, so the air pressure within the space is greater than that in surrounding areas; air flows out of positively pressurized spaces into negatively pressurized spaces; and can be a pathway for contaminants.

Re-entrainment – a situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and/or other openings in the building envelope.

Respirable Particles – particles that penetrate and are deposited in the nonciliated portions of the lung; particles greater than 10 micrometers in size are not respirable.

Scanning Electron Microscope – electron microscope that forms a three-dimensional image on a cathode-ray tube by moving a beam of focused electrons across an object and reading both the electrons scattered.

Serogroup – Serotype: a group of related microorganisms distinguished by its composition of antigens (a substance that stimulates the production of an antibody).

Sick Building Syndrome (SBS) – a term sometimes used to describe situations in which building occupants experience acute health and/or comfort effects that appear to be linked to time spent in a particular building, but where no specific illness or cause can be identified; complaints may be localized in a particular room or zone or may be spread throughout the building.

Speciation – identification of sampled microbe to the species level.

Specific Testing – various methods of testing utilized to qualify and/or quantify a specific type of contaminant (chemical, microbiological, particulate, etc.) thought to possibly be present in the environment.

Stack Effect – pressure-driven airflow produced by convection as heated air rises, creating a positive pressure area at the top of a building and a negative pressure area at the bottom of a building; the stack effect can overpower the mechanical system and disrupt ventilation and circulation in a building; can be found in association with elevator shafts, stairwells, laundry chutes, etc.; can be a pathway for contaminants.

Temperature – occupant thermal comfort is typically expected in most occupants if the temperature remains between 69-76F when relative humidity is between 30-60%

Thermophilic Bacteria – bacteria requiring high temperature for normal development.

Vapor – a substance that is in the gaseous form, particularly one near equilibrium with its condensed phase, which does not obey the ideal gas laws; generally, any gas below its critical temperature.

Vapor Pressure – pressure at which a vapor and its liquid exist in equilibrium.

Volatile Organic Compounds (VOCs) – compounds that evaporate from many housekeeping, maintenance, and building products made with organic chemicals; sufficient quantities of VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals, and some are suspected of causing or are known to cause, cancer in humans.

X-ray Diffraction – the scattering of x-rays by crystal atoms, producing a diffraction pattern that yields data about the structure of the crystal.

References & Organizational Links

American Council for Accredited Certification (ACAC)

American Industrial Hygiene Association (AIHA)

Board for Global EHS Credentialing (BGC) – formerly American Board Industrial Hygiene (ABIH)

National Center for Environmental Health (CDC)

Environmental Protection Agency (EPA)

Indoor Air Quality Association (IAQA)

Institute of Inspection Cleaning and Restoration Certification (IICRC)

American Biological Safety Association – one of the premier authorities on biological safety

Building Research Board; Committee on Indoor Air Quality; Building Diagnostics:  A Conceptual Framework; Washington, D.C., National Academy Press, 1985.

Webster’s II, New Riverside University Dictionary, The Riverside Publishing Company, 1984.

ASHRAE Standard 55-1992; American Society of Heating Refrigeration and Air Conditioning Engineers, Inc., 1992.

ASHRAE Standard 62-1989, American Society of Heating Refrigeration and Air Conditioning Engineers, Inc., 1989.

Building Air Quality, A Guide of Building Owners and Facility Managers; U.S. EPA, 1991.


NSF International 49-1992

NAFA Guide to Air Filtration, National Air Filtration Association, 1996.