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The following pages list the sources used statistics and other material in the descriptions for the concepts and the featuresin the WELL Building Standard TM.

Made by forcing hydrogen gas into oil at high pressure in order to increase the shelf life and prevent rancidity of an oil.
Inorganic Chemicals
Refers to a chemical compound that is not "organic". Broadly, compounds not containing carbon.
Necessary for healthy blood circulation, but excessive iron particles in water can provide a shelter for disease-causing bacteria.
Small amounts are required for a healthy diet, but higher amounts may cause neurological damage.
"Darkness hormone" whose levels in the body is regulated by the circadian rhythm and the presence of light and in humans acts a driver for sleep.
A naturally-occurring poisonous metal element which occurs naturally in the earth's surface.
Bacteria and microscopic algae and fungi, especially those living in a particular site or habitat.
Enters groundwater and surface water by dissolution of rocks and soils, from atmospheric fallout and biological decays and waste disposal.
Nitrogen Dioxide (NO₂)
A product of combustion mainly found near burning sources (for instance, wood smoke and traffic combustion).
A chemical that is required for metabolic processes, which must be taken from food or another external source. Macronutrients taken from food sources include carbohydrates, proteins, fats and vitamins.
Organic Chemicals
Broadly refers to chemical compounds that possess carbon-based atoms, generally found in biological systems.
Oxidized Lipids
A lipid, any of a diverse group of organic compounds including fats, oils, hormones and certain components of membranes that are grouped together because they do not interact appreciably with water, combined chemically with oxygen.
Triatomic form of oxygen. Hazardous to the respiratory system at ground level, but a layer in the upper atmosphere blocks much of the ultraviolet radiation from the sun.
Partially Hydrogenated Oil
Vegetable oils that have been hydrogenated or partially hydrogenated for the purpose of being solid at room-temperature, which contain trans-fats.
Particulate Matter
A complex mixture of elemental and organic carbon, salts, mineral and metal dust, ammonia and water that coagulate together into tiny solids and globules.
Perfluorinated Compound (PFC)
A family of fluorine-containing chemicals with unique properties to make materials stain- and stick-resistant.
A chemical that is made from petroleum or natural gas.
Polychlorinated Biphenyls (PCBs)
A former commercially produced synthetic organic chemical compound that may be present in products and materials produced before the 1979 PCB ban.
Polyunsaturated Fat
Polyunsaturated fats are among the “good” fats that can help reduce cholesterol levels and risk of heart disease and stroke. Polyunsaturated fats are found in sunflower, corn, soybean and flaxseed oils, walnuts and many fish.
A synthetic resin used chiefly in paints and varnishes. Diisocyanates in polyurethane products can be toxic if inhaled or touched during installation.
Polyvinyl Chloride (PVC)
An inexpensive plastic that is widely used for many objects. Exposure to its chemical precursors, additives and products of combustion can be harmful.
Radioactive, carcinogenic noble gas generated from the decay of natural deposits of uranium.
Saturated Fat
Typically solid at room temperature, saturated fats are found in high concentrations in salmon, butter, bacon, beef and cheese.
Neurotransmitter hormone produced in the gut and brain stem which regulates mood, sleep and digestion.
Widely used in agriculture as an herbicide to control weeds; high levels of simazine exposure over a short period can cause weight loss and blood damage.
Sodium is consumed as sodium chloride in common salt. It is a vital nutrient, but unhealthy in high amounts.
Sulfates occur naturally and can erode into water supplies; the health effects of sulfates are uncertain, but ingesting large amounts has been linked to negative health effects.
A chlorinated hydrocarbon used as a dry cleaning solvent, an additive in textile processing and metal degreasing that has been linked to cancer.
Any toxic substance, generally created by human activity.
A poisonous substance produced by a living organism.
Chlorine in water can combine with organic matter to form compounds called disinfectant byproducts (DBPs), such as trihalomethanes.
Ultrafine Particles
Also called nanoparticles, ultrafine particles are a subcategory of PM₂.₅ which are exclusively less than 0.1 µm. Due to the small size they are often airborne and can easily reach the alveoli of the lungs.
Urea-formaldehyde (UF)
A low-cost thermosetting resin that is used in the wood product industry.
Volatile Organic Compounds (VOCs)
Organic, and therefore carbon and hydrogen containing, materials which evaporate and diffuse easily at ambient temperature. VOCs are emitted by a wide array of building materials, paints and common consumer products.
Typical applications include solvents for the printing, rubber and leather industries as well as ingredients in paper and fabric coatings.
A-Weighted Decibel (dBA)
Acoustic decibel modified using "A-weighting" to adjust the frequency-dependent response of human hearing.
Air Changes Per Hour (ACH)
A measure of how many times the volume of air within a defined space is replaced, used in the context of building ventilation and air tightness.
Annual Sunlight Exposure (aSE)
Percentage of space in which the light level from direct sun alone exceeds a pre-defined threshold (such as 1000 lux) for some quantity of hours (such as 250) in a year.
Candela (cd)
Measurement of luminous intensity and the SI base unit of light.
Clothing Insulation (CLO)
Clothing insulation is the resistance to heat transfer provided by clothing measured in clo (1 clo = 0.155 m²K/W = 0.88°F ft²h/BTU).
Color Rendering Index (CRI)
Comparison of the appearance of 8 to 14 colors under a light source in question, to a blackbody source of the same color temperature. CRI or Ra refers to the average of the first 8 comparisons and R9 describes the lighting accuracy on red surfaces.
Correlated Color Temperature (CCT)
Spectral distribution of electromagnetic radiation of a blackbody at a given temperature. For example, the color temperature during the daytime is approximately 15,000 K, while during sunset is approximately 1,850 K.
Cubic feet per minute (CFM)
Measures the mass of gas that passes through a certain point.
Decibel (dB)
A unit of measurement for sound. The decibel is a logarithmic unit so an increase in 10 decibels equals an increase by a factor of 10.
Dry Bulb Temperature (DBT)
Temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture. This temperature is usually thought of as air temperature and it is the true thermodynamic temperature. Dry bulb temperature does not take humidity into account.
Equivalent Continuous Level (LAeq)
The time averaged sound pressure level on the A-weighted scale, converted to decibels.
Equivalent Melanopic Lux (EML)
A measure of light used to quantify how much a light source will stimulate melanopsin’s light response.
Footcandle (fc)
Unit of illuminance, equivalent to one lumen per square foot.
Frequency (f)
The number of times an event repeats itself per a specified unit of time. Hertz (Hz) is a common unit for frequency and equals cycles per second i.e. 1 Hz = 1 cycle/second. Most commonly used with waves (sound and light) and is the number of times the wave repeats itself at its particular wavelength.
Illuminance (Lux)
Amount of light passing through a given area in space. Measured in lux or foot-candles.
Impact Insulation Class (IIC)
Extent to which a physical structure blocks out sound, typically used in describing flooring, a higher IIC reduces footfall noise, and other impact sounds.
Light Reflectance Value (LRV)
Rating from 0 (black) to 100 (white) describing the amount of visible and usable light that reflects from (or absorbs into) a painted surface.
Measure of luminous flux, derived from the SI base unit candela, and therefore weighted to the eye's sensitivity to light; 1 W of light at 555 nm equates to 683 lumens.
Luminance (cd/m²)
Measurement of how bright a surface or light source will appear to the eye. Measured in candela/m² or foot-lamberts.
Luminous Flux
Total luminous output of a light source, measured in lumens. Weighted to the eye's visual sensitivity.
Luminous Intensity
Radiant power weighted to human vision, describing light emitted by a source in a particular direction. Measured by the candela.
Unit of illuminance, one lux being equivalent to one lumen per square meter.
Maximum Contaminant Level Goal (MCLG)
Concentration of a substance in drinking water believed to result in no adverse effects. Derived from on Population Adjusted Dose and estimated daily water consumption, fraction of exposure from water and body weight.
Maximum Contaminant Levels (MCL)
Enforceable water quality limits for a substance, based on the Maximum Contaminant Level Goal, but taking into account technology and cost limitations of treatment.
Mean Radiant Temperature (MRT)
The uniform surface temperature of an imaginary black enclosure in which an occupant would gain or lose the same amount of radiant heat as in the actual non-uniform space; MRT is a primary driver of human thermal comfort, roughly equal in influence to air temperature.
Metabolic Rate (MET)
Rate that chemical energy in the body is converted to heat and mechanical energy.
Roughness rating of a physical surface, averaged in micro-meters & micro-inches.
Milliwatt (mW)
Unit of measurement for electromagnetic radiation, equal to 1/1000 watt. Not weighted to biological responses such as vision.
Minimum Efficiency Reporting Value (MERV)
Value assigned to an air filter to describe the amount of different types of particles removed when operating at the least effective point in its life.
Nephelometric Turbidity Units (NTU)
Measure the turbidity of water.
Noise Criteria (NC)
Define the sound pressure limits of the octave band spectra ranging from 63-8000 Hz. The noise criteria equals the lowest curve which is not exceeded in the spectrum.
Noise Isolation Class (NIC)
Field test for determining the sound transmitting abilities of a wall. Higher NIC values indicate better sound insulation i.e. more effective sound cancellation between spaces. NIC specifications are defined in ASTM Standard E366.
Noise Reduction Coefficient (NRC)
Average value that determines the absorptive properties of materials.
Parts per Billion (PPB)
Measurement of the mass of a chemical or contaminate per unit volume of water.
Parts Per Million (PPM)
A unit of measurement to express very dilute concentrations of substances.
PicoCurie per Liter (pCi/L)
A non-SI unit of radioactivity.
Relative Humidity (rH)
Ratio of partial pressure of water vapor in the air to the saturation pressure of water vapor at the same temperature and pressure.
Reverberation Time (RT)
Time it takes for sound to decay. The most commonly used reverberation time is RT60, the time it takes for the sound level to decrease 60 decibels. Additional reverberation time measurements are RT20 and RT30, for decreases of 20 and 30 decibels, respectively.
Sound Pressure Level (SPL)
Sound pressure level (SPL), also known as acoustic pressure, is the pressure variation associated with sound waves. Usually measured in decibels, the acoustic pressure is a ratio between the measured value and a reference value; a common reference is threshold of hearing or the minimum sound level that the average person can hear.
Sound Transmission Class (STC)
A laboratory method for determining the sound transmission through a wall. Higher STC values indicate more effective noise isolation than lower ones. STC specifications are found in ASTM Standards E90-09 and E1425.
Spatial Daylight Autonomy (sDA)
Percentage of floor space where a minimum light level (for example 300 lux) can be met completely for some proportion (for example 50%) of regular operating hours by natural light.
Visible Transmittance (VT)
Amount of light in the visible portion of the spectrum that passes through a glazing material.
Walk Score®
A walkability index based on the distance to amenities such as grocery stores, schools, parks, libraries, restaurants, and coffee shops. Scores are normalized from 0 to 100 points and are based on an algorithm that awards maximum points to amenities within a 5 minute walk distance or 400 m [0.25 mi], and a decay function assigns points for amenities up to 30 minutes away.
Wavelength (λ)
The distance between two points on a wave in which the wave repeats itself. Often used to describe light waves.
The concentration of an air pollutant (e.g. ozone) is given in micrograms (one-millionth of a gram) per cubic meter air or µg/m3.