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The physiological process by which toxicants pass body membranes and enter the bloodstream or other body components from the site of exposure.


American Conference of Governmental Industrial Hygienists.


Air changes per hour. One ACH means a volume of outdoor air equal to the volume of the space being ventilated has entered that space in one hour.


A condition involving relatively brief periods of time. For CO exposure, acute is defined as an exposure of up to 10-15 hrs or less, involving one major exposure.

Acute effects

Those that occur immediately on exposure.


Americans with Disabilities Act of 1990.

Additive effect

A biological response to exposure to multiple chemicals which is equal to the sum of the effects of the individual agents.


Inability to perceive objects through otherwise normally functioning sensory channels.


Asbestos Hazard Emergency Response Act.


Air handling unit refers to ventilation equipment in HVAC systems.

Air Cleaning

An IAQ control strategy to remove various airborne particles and/or gases before the air enters the occupied space. The three types of air cleaning most commonly used are particulate filtration, electrostatic precipitation, and gas absorption.

Air Exchange Rate

Used in two ways. First, the number of times that the outdoor air replaces the volume of air in a building per unit time, typically expressed in air changes per hour; second, the number of times that the ventilation system replaces the air within a room or area within the building.

Air infiltration

Air leakage into a building.


Inability to initiate changes in activity and to perform ordinary volitional movements rapidly and easily. It is the most disabling feature of Parkinson's disease.


A substance capable of causing an allergic reaction because of an individual's sensitivity to that substance.


(plural = alveoli) A small microscopic sac that is the functional unit of the lung, the location at the far end of the respiratory tract where gas exchange occurs.


A unicellular organism which may either obtain energy by means of photosynthesis or by ingesting other organic material. The organism has no wall or coat outside its cell membrane; it moves and feeds by means of pseudopodia.

Amygdala (amygdaloid nucleus)

Coordinates autonomic and endocrine responses in conjunction with emotional states; part of the limbic system.


A disease marked by brief, sudden attacks of chest pain precipitated by a deficient supply of oxygen to the heart muscles (also known as angina of the chest or angina pectoris).

Animal dander

Tiny scales of animal skin.

Antagonistic effect

A biological response to exposure to a single chemical interfering with the action of another or to multiple chemicals interfering with each other's actions.


A remedy to counteract the effects of a poison.


Agent that kills microbial growth. See disinfectant, sanitizer, and sterilizer.


Disturbances of language ability.


Inability to perform complex acts requiring sequences of muscle contractions or a planned strategy.


The ability of a filter to remove injected standard dust from the test air. It is calculated as a % relationship on a weight basis.


American Society of Heating, Refrigeration, and Air Conditioning Engineers.


Substances that starve the cells of an individual from the life-giving oxygen needed to sustain metabolism.


Quick arrhythmic movements that occur due to brief interruptions in background tonic muscular contractions.


American Society for Testing and Materials.


abnormalities in the execution of voluntary movements.


Inability to sustain muscles of the fingers, toes, tongue or any other group of muscles in one position; maintained posture is interrupted by continuous slow, purposeless movements.


A genetically controlled predisposition to production of specific antibodies. Approximately 10% of the population suffer from this problem. Specific diseases include allergic rhinitis (hayfever), asthma, and atopic dermatitis.


Microorganisms that have no true nucleus, a single chromosome, and no mitochondria, capable of causing adverse health effects.


A process whereby an unoccupied building is maintained at elevated temperatures to enhance the emission of VOCs prior to the occupation of the building, in the theory that the VOCs will be ventilated out of the building. This practice is controversial and not without risk of incurring other types of problems.

Balint's Syndrome

Due to bilateral damage to the parietal-occipital regions; causes problems with visually guided motor movements.

Basal Ganglia

Made up of the caudate nucleus and putamen (known together as the corpus striatum) and the globus pallidus. Roles in regulating movement and cognition. Damage to it causes seizure disorders, multiple-sclerosis-type disorders, decrement in intellectual capacity, judgment, ability to concentrate, memory, speech capability.


Tiny airborne particles that are alive, were once alive, or are a part of something that is or once was alive.


A physical or chemical agent that is capable of killing microorganisms.


A surface layer of micro-organisms.

Biological Contaminants

Agents derived from or that are living organisms (e.g., viruses, bacteria, fungi, and mammal and bird antigens) that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases. Also referred to as microbiologicals or microbials.

Breathing Zone

Area of a room in which occupants breathe as they stand, sit, or lie down.


See Building-Related illness

Broca's area

Region of the frontal lobe on left, that makes spoken language possible.


The two respiratory tubes branching into the two lungs at the lower end of the trachea. They branch into progressively smaller passageways, the bronchioles, and finally reach the alveoli, the location where gas exchange occurs.

Building Envelope

Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.

Building-related illness

A discrete, identifiable disease or illness that can be traced to a specific pollutant or source within a building. (e.g., Legionnaires' disease, hypersensitivity pneumonitis). Contrast with sick building.


The comparison of an instrument response to known values of a parameter being measured.


A disease characterized by malignant, uncontrolled cell growth in body tissue.


A substance capable of producing cancer in a living organism.

Caudate Nucleus

Part of basal ganglia; damage causes forms of aphasia.


Constant Air Volume - Refers to a type of HVAC system where air volume is constant and airstream is either heated or cooled so as to maintain a constant temperature.

Ceiling Plenum

Space below the flooring and above the suspended ceiling that accommodates the mechanical and electrical equipment and is used as part of the air distribution system. The space is kept under negative pressure.

Cellular toxicant

A chemical which acts as a poison by temperature to meet heating and cooling needs.

Cephalea (cephalgia)

Headache, pain in the head.


Occupies most of the posterior cranial fossa; damage produces ataxia, slurring of speech.

Cerebral Cortex

Expansive mass of brain tissue covering the older parts of the brain including cerebral hemispheres and formed of sulci, consisting of 4 parts (frontal, parietal, occipital, temporal); 6th division of the C.N.S.; involved in vision, hearing, learning, memory, association, etc.

Cerebral Hemispheres

Made up of the basal ganglia, hippocampus and amygdala; overlaid by cerebral cortex; affects emotion, learning.


Cubic feet per minute

Chemical sensitivity

Health problems characterized by effects such as dizziness, eye and throat irritation, chest tightness, and nasal congestion that appear whenever individuals are exposed to certain chemicals. People may react to even trace amounts of chemicals to which they have become sensitized.

Cheyne Stokes

Characterized by rhythmic waxing and waning of the depth of ventilation, with a regular pattern of apnea, hyperventilation, etc.


Widespread arrhythmic movements of a forcible, rapid, jerky, restless type; movements are irregular and variable, but continuous. They may be simple or quite elaborate, and affect any part of body. Can be caused by damage to caudate nucleus.


A condition involving relatively long periods of time. For CO exposure, chronic is defined as an exposure of 10-15 hrs or more, and may involve one or cycles of exposure.

Chronic effects

Those occurring after repeated long-term exposure and are seen months or years after initiation of exposure.


(Interagency) Committee on Indoor Air Quality.


Short, specialized extensions of cells that appear hair-like, often arranged in rows, and present in large numbers. In the human respiratory system, cilia act to propel mucous slowly upwards, removing captured foreign particles.


Air moved through the furnace heat exchanger and then through the house to provide heating or cooling. This may not have any outside air.


Visually free of sludge, sediment, slime, algae, fungi, rust and scale.


Physical and/or chemical removal of scale, corrosion, biofilm, sludge, sediment and extraneous matter.


Carbon monoxide


Carbon dioxide


Component of HVAC system that acts as a heat exchanger, either adding heat or taking heat away from the air stream.

Colony Forming Unit (cfu)

A colony arising from a viable unit of one bacterium or more in a clump. For statistical significance, only those plates with 30 to 300 cfu's are selected for counting.


Additional air brought into the house to allow furnaces, boilers, clothes dryers, ranges and domestic hot water heaters to burn. If the appliance has "sealed" combustion this air will not affect the air within the house.


Start-up of a building that includes testing and adjusting HVAC, electrical, plumbing, and other systems to assure proper functioning and adherence to design criteria. Commissioning also includes the instruction of building representatives in the use of the building.


The process of changing a vapor to a liquid by extracting heat from the vapor.

Conditioned air

Air that has been heated, cooled, humidified, or dehumidified to maintain an interior space within the comfort zone (Sometimes referred to as tempered air).


The ability of water to conduct electricity. Conductivity measurement is used for estimating the amount of total dissolved solids in water.

Constant Air Volume (CAV) System

Refers to a type of HVAC system where air volume is constant and airstream is either heated or cooled so as to maintain a constant temperature.

Constant volume systems

Air handling systems that are designed to provide constant airflow and vary air.


Movement of molecules (gases) from a region of higher air pressure to a region of lower air pressure. Airflow can also be induced by a temperature gradient (e.g., stack effect).


Consumer Product Safety Commission

Criteria Air Pollutants

Include sulfur dioxide, particulates, lead, ozone, nitrogen oxides, and carbon monoxide, all designated by the EPA and which have national standards under the National Ambient Air Quality Standards (NAAQS).

Cyclic patterns of symptoms

One or more symptoms which occur at regular intervals (e.g., every morning).


Controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable, or part of an automated control system.


A length of pipe ending at a fitting through which water flows only when the fitting is opened.


A cleansing agent capable of penetrating biological films, sludge and sediment and having the ability to emulsify oil and hold materials in suspension. Water treatment specialist have developed detergent formulations which are capable of thoroughly cleaning components which are difficult to access and inspect, such as cooling tower fill.

Developmental toxicant

A chemical that acts as a poison by means of causing adverse effects on the developing organism, including death, structural abnormality, altered growth, and functional deficiency.



Investigation or analysis of the cause or nature of a condition, situation, or problem.


5th division of the C.N.S.


Additional air beyond that which is needed to provide combustion. This may either be within the combustion chamber as excess air or as induced flow in the exhaust stack.


A glass or plastic slide coated with culture media on which microorganisms can be grown and estimated. Legionella does not grow on these media.


One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a disinfectant when it destroys or irreversibly inactivates infectious or other undesirable organisms, but not necessarily their spores. EPA registers three types of disinfectant products based upon submitted efficacy data: limited, general or broad spectrum, and hospital disinfectant.

Dose-response relationship

The effect of a substance on a body increases as the dose increases; theoretically, the body may respond differently at different dose levels of a given substance.

DPD Test Kit

A kit for measuring free, combined and total chlroine residuals using the reagent DPD (N, N-diethyl-p-phenylene diamine). Many test kits available from swimming pool suppliers measure only total chlorine not free chlorine and consequently should not be used. Free chlorine residuals in excess of 10 mg/L 10 ppm) are capable of bleaching the indicator colour, rendering the test invalid. Samples of water may have to be diluted with distilled water, or other water which does not interfere with the test, to bring the sample within the range of the kit. Allowance must be made for the sample dilution factor when determining the free chlorine residual in the original sample.

Dust spot efficiency

A measure (expressed in percent) of the ability of a filter to remove atmospheric dust from air.


Difficulty speaking.


Inability to carry out mathematical calculations.


Disorders with reading; congenital or acquired.


Difficulty swallowing.


Abnormally increased muscular tone that causes fixed abnormal postures; sometimes shifting postures result from irregular, forceful twisting movements that affect the trunk and extremities.


Limited ability to speak unless spoken to; response usually a direct echo of examiner.


Bacterial by-products excreted into the environment.

Environmental Agents

Conditions other than indoor air contaminants that cause stress, comfort, and/or health problems (e.g., humidity extremes, drafts, lack of air circulation, noise, and overcrowding).


Acronym for the U.S. Environmental Protection Agency, the Federal agency responsible for the regulation of pesticides, toxic chemicals, hazardous wastes, and toxic pollutants in water and air.


The study of the incidence, distribution, and control of disease in a population.


Applied science that investigates the impact of people's physical environment on their health and comfort (e.g., determining the proper chair height for computer operators).


Acronym for Environmental Tobacco Smoke. ETS is made up of the smoke emanating from the burning end of a cigarette and smoke that is inhaled by the smoker, and consists of over 4,700 compounds, including both gases and particles.


Air removed form the house through fans. Typical examples are bathroom exhaust, and kitchen hoods.

Exhaust ventilation

Mechanical removal of air from a portion of a building (e.g., piece of equipment, room, or general area).


The initial contact of the body with a substance.

Exposure assessment

Analysis of a set of exposure profiles which address for each pollutant, the size of the exposed population, and the routes, duration, frequencies, and intensities of exposure.

Extra-pyramidal Signs

May different phenomena which are due to primary deficits (negative symptom) or new de-inhibited actions that have appeared due to lesions associated with the basal ganglia.

False negative

Test or investigation results that indicate a particular condition does not exist when it actually does.



Federal Insecticide, Fungicide, and Rodenticide Act.

Free Chlorine Measurement

The measurement of hypochlorous acid (an efficient disinfectant) and hypochlorite ion ( a poor disinfectant) in water. The ratio of these two materials in water is pH dependent. The pH range specified (7.0 to 7.6) ensures that sufficient hypochlorous acid is present to facilitate effective disinfection.


Refers to solid particles generated by condensation of vapors or gases, generally after volatilization from combusted melted substances. Popular usage sometimes loosely includes any type of contaminant.


Any of a group of parasitic lower plants, including molds and mildews, that lack chlorophyll.

Gas Sorption

Devices used to reduce levels of airborne gaseous compounds by passing the air through materials to extract the gases. The performance of solid sorbents is dependent on the airflow rate, concentration of the pollutants, presence of other gases or vapors, and other factors.


Individual atoms or molecules that spread evenly throughout a volume of air, and cannot be collected by ordinary particulate filters.

Globus Pallidus

Part of the basal ganglia. Damage can result in flexion dystonia, impaired postural reflexes.

Goblet cell

Specialized cell found in the human respiratory system that serves to secrete mucus.


Non-regulatory recommendations on how to achieve specific objectives.

Habit Spasms

Seemingly voluntary movements but which individuals feel compelled to do to relieve tension (eg. sniffing, clearing of throat, pulling on collar).

Hazardous Air Pollutants

189 chemicals considered by the EPA to be hazardous to human health.

Health Canada, Health Protection Branch

Material Safety Data Sheets with health and safety Information on Infectious microorganisms. Including Aspergillus and other molds and airborne biologicals.
(613) 957-1779


Hyperkinetic movement disorder characterized by violent flinging motions in the arm contralateral to a lesion in or near the subthalamic nucleus. May be due to damage in basal ganglia.


Neural motor condition affecting one side of the body only. Paraplegia affects both sides.


Neural motor condition affecting one side of the body only. Paraplegia affects both sides.


Part of the limbic system; involved in memory storage; damage produces effects on short- to long-term memory, limbic system.


A device to add moisture to air.

Humidifier fever

A respiratory illness that may be caused by exposure to toxins from microorganisms found in wet or moist areas of humidifiers and air conditioners. Also called air conditioner fever or ventilation fever.



A device, actuated by changes in humidity, used for the automatic control of relative humidity.


Acronym for heating, ventilating, and air conditioning system.

Hydronic Heat

Heat transferred from a boiler, to conditioned water, to a radiator in the living space (Called hydropic because water [hydro-] is the medium of heat transfer).

Hypersensitivity Diseases

Diseases characterized by allergic responses to animal antigens. The hypersensitivity diseases most clearly associated with indoor air are asthma, rhinitis, and hypersensitivity pneumonitis. Hypersensitivity pneumonitis is a rare but serious disease that involves progressive lung damage as long as there is exposure to the causative agent.

Hypersensitivity Pneumonitis

A group of respiratory diseases that involve inflammation of the lungs. Most forms are thought to be caused by an allergic reaction triggered by repeated exposures to biological contaminants.


Abnormally decreased mobility; abnormally decreased motor function or activity.


Controls pituitary; regulates temperature, heart rate, blood pressure, food and water intake (autonomic functions, multi-glandular control); constitutes less than 1% of brain.


Acronym for Indoor Air Quality. EPA's Indoor Air Quality Information Clearinghouse (1-800-438-4318 or 301-585-9020).


Indoor Air Quality Association, Inc.


When the body's natural defenses to infection are below normal.

Indicator Compounds

Chemical compounds, such as carbon dioxide, whose presence at certain concentrations may be used to estimate certain building conditions (e.g., airflow, presence of sources).


Substances which inflame living tissue by chemical action at the site of contact, causing pain or swelling.

Legionnaires' disease

An illness which is sometimes fatal and whose symptoms mimic pneumonia. It is caused by a bacterium (Legionnella pneumophila) and primarily attacks immunocompromised individuals.


A large phagocytic cell found in the lung tissues that helps defend the body against viruses, bacteria, and other foreign intruders, generally by engulfing them.

Make up

Air which enters the house, either intended or not, to replace the air removed through exhaust and dilution.

Make-up Air

Air brought into a building from the outdoors through the ventilation system, which has not been previously circulated through the system.


Operation of an IAQ program-including personnel and budgeting decisions, monitoring and feedback, legislative initiatives, internal information flows, and enforcement of State requirements.


Multiple Chemical Sensitivity. A term used by some people to refer to a condition in which a person is considered to be sensitive to a number of chemicals at very low concentrations. There are a number of views about the existence, potential causes, and possible remedial actions regarding this phenomenon.

Medulla Oblongata

2nd division of the C.N.S.


In toxicology, refers to the biochemical changes that a chemical undergoes in the body.

mg/L (ppm)

Milligrams per liter (parts per million). For practical purposes mg/L is assumed to be equal to ppm.


Microscopic forms of life.

Microbiological Contamination

Infection or pollution by microscopic organisms.


Agents derived from or that are living organisms (e.g., viruses, bacteria, fungi, and mammal and bird antigens) that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases. Also referred to as microbiologicals or microbials.


Characterized by very small, cramped handwriting.


4th division of the C.N.S.


Mist is a term loosely applied to any dispersion of liquid particles, many of which are large enough to be individually visible without visual aid.


Growth produced by any of a large group of fungi which has a cottony or furry appearance.


Material Safety Data Sheet


Mucus droplets are secreted by specialized cells in the respiratory system, mucus currents, swept by cilia remove foreign particles from the trachea.

Multiple Chemical Sensitivity (MCS)

A term used by some people to refer to a condition in which a person is considered to be sensitive to a number of chemicals at very low concentrations. There are a number of views about the existence, potential causes, and possible remedial actions regarding this phenomenon.


Substances that induce a permanent change in the genetic material.



Unable to speak, inarticulate; inability or refusal to speak.



Metabolites produced by fungi that have a broad spectrum of toxic effects ranging from mild acute toxicity to potent carcinogenicity.


Very brief, involuntary, random muscular contractions. Myoclus can occur spontaneously at rest, in response to sensory stimuli, or with voluntary movements.

Natural ventilation

Occurs when outdoor air enters through open windows and doors and through cracks and leaks in the home.

Negative Pressure

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.


Substances that prevent normal function of the central nervous system.


National Institute for Occupational Safety and Health (U.S.A.)

Occupational Standards

Maximum pollutant concentration levels, usually set by the Occupational Safety and Health Administration (OSHA).


The production of gases from the chemical deterioration of a substance over time.


Acronym for the Occupational Safety and Health Administration, a part of the U.S. Department of Labor responsible for determining whether employers are providing working conditions that are safe for employees.


Solids or liquids light enough to be suspended in air.


Disease-producing microorganisms or materials.


Permissible Exposure Limits (standards set by OSHA), workplace exposure limits established to protect on-the-job workers.


A term used to describe the hydrogen ion activity of a water system. A solution of pH 0 to 7 is acid, pH of 7 is neutral, pH 7 to 14 is alkaline.


An air compartment connected to a duct or ducts.


Preventive Maintenance


Recommendations defining responsibility and action.

Pollutant pathways

The routes followed by a pollutant from its emission (source) as it travels through a strucducts, air streams, etc.

Pons (+ cerebellum)

3rd division of the C.N.S.

Pontiac Fever

A flu-like illness caused by Legionnella or a similar bacterium named after a 1968 outbreak in Pontiac, Michigan.

Positive Pressure

Condition that exists when more air is supplied to a space than is exhausted, so that air pressure within that space is greater than that found in surrounding areas.

Psychosocial Factors

Psychological, organizational, and personal stressors that could produce symptoms similar to poor indoor air quality.

Public information

Development and dissemination of both technical and non-technical IAQ information to homeowners, private companies, the media, local officials, and other concerned parties.

Pulmonary Toxicants

Substances that affect the respiratory tract.

Purkinje Cells

A type of cell found in the cerebellar cortex.



Part of basal ganglia.


Quality Assurance/Quality Control procedures are used to assess method performance, accuracy, and precision.

Radiant Heat Transfer

Radiant heat transfer occurs when there is a large difference the temperatures of two No surfaces that are exposed to each other, but are not touching.


A radioactive gas formed by the decay of uranium.

Radon progeny

Radon particles that can be breathed into the lung, where they continue to release radiation as they further decay. Also known as radon decay products or radon daughters.


Situation that occurs when the air being exhausted from a building is immediately brought back into the system through the air intake and other openings in the building envelope.


Recommended Exposure Limits (recommendations made by NIOSH)

Reproductive Toxicant

A chemical acting as a poison by means of causing adverse effects on the male or female reproductive system (e.g. fertility, pregnancy outcomes).

Respirable Particles

Those particles found in air that are capable of penetrating and being deposited in the deeper (non-ciliated) portion of the lung.


Muscle tone is high and there is continuous contraction and resistance to passive movement.


One of three groups of antimicrobials registered by EPA for public health uses.' EPA considers an antimicrobial to be a sanitizer when it reduces, but does not necessarily eliminate, all the microorganisms on a treated surface. To be a registered sanitizer, the test results for a product must show a reduction of at least 99.9% in the number of each test microorganisms over the parallel control.


Depending at least in part on dead organic matter as a food source.


Acronym for the Superfund Amendments and Reauthorization Act of 1986. Title IV of this Act requires EPA to establish a research program for radon gas and IAQ and to disseminate information on IAQ problems and solutions based on current research.


Sick Building Syndrome. Term that refers to a set of symptoms affecting a number of building occupants during the time they spend in the building and diminish or go away during periods when they leave the building. Cannot be traced to specific pollutants or sources within the building. (Contrast with Building-Related Illness.)

Sodium Hypochlorite

A chlorine-releasing material used for disinfection. The strength of sodium hypochlorite solution reduces on storage.

Soil Gases


Gases that enter a building from the surrounding ground (e.g., radon, volatile organics, pesticides).


A substance used for either absorption or adsorption.

Source emissions

Emissions generated at the origin of a pollutant.

Stack effect

Occurs when a house acts like a chimney. The warm air in the home is lighter than the cold air outside and rises in the building and escapes out the top. The cool air is drawn into the building as the warm air escapes.

Staged Approach

A systematic, step-wise approach to investigation providing built-in decision points at which progress is assessed, and the investigation is redirected as necessary.


Usually, mandatory guidance which is founded on statutory authority and involves an enforcement program; however, sometimes used to refer to non-regulatory guidance (e.g., ASHRAE ventilation standards).

Static Pressure

Condition that exists when an equal amount of air is supplied to and exhausted from a space. At static pressure, equilibrium has been reached.


Short-term exposure limit


One of three groups of antimicrobials registered for public health uses. EPA considers an antimicrobial to be a sterilizer when it destroys or eliminates all forms of bacteria, fungi, viruses, and their spores. Because spores are considered the most difficult form of a microorganism to destroy, EPA considers the term sporicide to be synonymous with sterilizer.


Identification of objectives, measures of success, authority, overall resource commitment, coordination efforts, and level and timing of activities.

Substantia nigra

An area of the midbrain. Lesions can result in akinesia. Due to tremor at rest of Parkinson's disease.

Subthalamic nuclei

An area within the basal ganglia.


A soluble surface acting agent that reduces surface tension between particulate matter and water.


Faint; loss of consciousness.

Systemic Toxicants

Substances that affect entire organ systems, often operating far from the original site of entry.


Increase in heart rate.

TEAM Studies

Acronym for Total Exposure Assessment Methodology Studies. The goal of these long-term series of EPA-conducted studies is to determine the actual exposure of people to a substance or substances.


Part of cerebral hemispheres; process information reaching the cerebral cortex from rest of C.N.S.

Thermal Bridge

A heat-conductive element in a building assembly that extends from the warm to the cold side and provides less heat-flow resistance than the adjacent construction.

Thermal Discomfort

The sensation of being too cold or too warm.


The lowest dose of a chemical at which a specific measurable effect is observed. Below this dose, the effect is not observed.


The lowest dose of a chemical at which a specific measurable effect is observed. Below this dose, the effect is not observed.


Threshold limit value


Threshold Limit Values are the recommended concentrations of airborne contaminants to which workers may be exposed according to the ACGIH.


Total Bacteria Count (TBC)

An estimate of the number of viable units of bacteria per milliliter of water under the conditions of testing. Note that no single method, culture medium or conditions of incubation can satisfy the growth requirements of all bacteria in a water sample.

Total dissolved solids

The total weight of dissolved substances in water, including those which are capable of conducting electricity and those which are not.


Harmful, poisonous.

Toxic Air Pollutants

Aggregate emissions of the following are determined by the EPA to be toxic -Benzene, 1,3 Butadiene, Polycyclic Organic Matter, Acetaldehyde, Formaldehyde.


A poison.


The innate ability of a contaminant to cause injury to biological tissue.


The study of the adverse effects of chemicals on living organisms.

Tracer Gases

Compounds, such as sulfur hexafluoride, which are used to identify suspected pollutant pathways and quantify ventilation rates. Tracer gases may be detected qualitatively by their odor or quantitatively by means of air monitoring equipment.



A tube which conducts air, also known as the windpipe in humans; the first main branch leading down from the throat towards the lungs.


Rhythmic oscillations of a part of the body around a fixed point; usually involve the distal parts of limbs, the head, tongue or jaw.



Toxic Substances Control Act.


An infection associated with crowding and inadequate ventilation; characterized by the formation of tubercles, wasting away of tissue, etc., often in the lungs.


A cloudy appearance in water that is caused by a suspension of colloidal or particulate matter.


Total volatile organic compounds.


Time-weighted average. The average exposure an individual would experience over the period of an entire shift (usually 8 hours), measured at the breathing zone.


Vapors represent the gaseous phase of a substance that is normally liquid or solid at room temperature and atmospheric pressure.

Variable Air Volume (VAV) systems

Air handling systems designed to condition air to a constant temperature and vary airflow to ensure thermal comfort.


A minimum amount of air required for IAQ and moisture control. This may be natural through leaks and infiltration or controlled in a tight house through a heat exchanger.

Ventilation Air

Defined as the total air, which is a combination of the air brought into a system from the outdoors and the air that is being recirculated within the building (Sometimes used to refer only to air brought into a system from the outdoors).

Ventilation Rate

The rate at which outside air replaces indoor air (also referred to as air exchange rate), expressed in one of two ways-the number of changes of outside air per hour (ACH), or the rate at which a volume of outside air enters per unit of time (cubic feet per minute, or cfm).


The smallest of all life forms containing either RNA or DNA. Viruses are responsible for a variety of human infections.


Volatile Organic Compounds. Compounds that evaporate from housekeeping, maintenance, and building products made with organic chemicals. These compounds are released from product that are being used and are in storage. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans. At present, not much is know about what health effects occur at the levels of VOCs typically found in public and commercial buildings.

Volatile Organic Compounds (VOCs)

Compounds that evaporate from housekeeping, maintenance, and building products made with organic chemicals. These compounds are released from product that are being used and are in storage. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans. At present, not much is know about what health effects occur at the levels of VOCs typically found in public and commercial buildings.


Acronym for the World Health Organization.