D Safe G:  Director of General Safety.

DA:   Distribution apportionment; the relationship between the proportion of the outside air (OA) quantity being delivered to portion a building and the proportion of the people in the building that are actually located in that portion of the building.

DACME:  Director Ammunition Clothing and Material Engineering.

Dado:  A rectangular groove cut into wood.

Dalton:  Measure of molecular mass.

Dalton’s Law:  States that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the constituent gases. The partial pressure is the pressure each gas would

Damper:  This is a plate that can be opened or closed to control and balance the airflow throughout the air handler’s ductwork. This control is most obvious in systems with a ‘zoning’ option where cooling can be confined or regulated in individual rooms.

Dampers:   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.

Dampproofing:  The process of coating the interior or exterior of a foundation wall, f1oor, etc., with bituminous emulsions or plastic cements. The purpose of dampproofing is to prevent or interrupt the capillary draw of moisture into the wall or floor system and to the interior of the foundation.

Dander:  Pronunciation (dan′dĕr).  (1.)  A fine scaling of the skin and scalp. See also: dandruff.  (2.)  A normal effluvium of animal hair or coat capable of causing allergic responses in atopic persons.

DAOD:  Defense Administrative Order and Directive.

Darby: A flat tool used to smooth concrete flatwork immediately after screeding. See Bullfloating.

DASD:  Direct Access Storage Device. These are more commonly known as disk drives. A string of DASD refers to multiple units lined up in a row.

Data-Logger:  An instrument which accepts and stores environmental or other data electronically ready for subsequent downloading into a computer for analysis.

Data Comm. Cabinet:  A tall cabinet used to house hubs, modems, multiplexers, routers and other data communications equipment.

Data Quality Objectives (DQOs):  Qualitative and quantitative statements of the overall level of uncertainty that a decision-maker will accept in results or decisions based on environmental data. They provide the statistical framework for planning and managing environmental data operations consistent with user’s needs.

Data Set: A set of subjective and physical data obtained simultaneously in a comfort survey.

Daughter Nuclide:  Nuclide formed by the radioactive decay of another nuclide, which is called the parent.

Daylight:  Visible part of global solar radiation. (Note: when dealing with the thermal effects of optical radiations, this term is commonly used for radiations extending beyond the visible region of the spectrum.)

Daylight Factor:  Ratio of the illuminance at a given point on a given plane due to the light received directly or indirectly from a sky of assumed or known illuminance distribution, to the illuminance on a horizontal plane due to an unobstructed hemisphere of this sky. The contribution of direct sunlight to both illuminances is excluded. (Notes: (1.) glazing, dirt effects, etc. are included. (2.) when calculating the lighting of interiors, the contribution of direct sunlight must be considered separately.)

Daylighting: Bringing sunlight deeper into a building to minimize the use of mechanical lighting.

DB (Decibels):  A unit to measure sound.

dbA: Sound-pressure level corrected to the “A” weighing network.

DC:  Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.

DC Motor:  A heavy-duty electric motor designed for continuous operation.

DCOS:  Deputy Chief of Staff.

DCOS FHP:  Deputy Chief of Staff Force Health Protection.

DCPEP:  Director Construction Projects and Engineering Policy.

DCSEM:  Director Combat Support Equipment Management.

DDC:   Direct digital control.

De Minimis Risk:  A level of risk that the scientific and regulatory community asserts is too insignificant to regulate.

Dead End Filtration:  Feed stream flows in one direction only, perpendicular to and through the filter medium to emerge as product or filtrate.

Dead End Pressure:  Is the suction pressure attained by an ejector or positive displacement vacuum pump at zero capacity with the suction absolutely blanked off.

Dead Load: The constant, design-weight (of the roof) and any permanent fixtures attached above or below.

Deaeration:  Act of separating air from fluids.

Death: The absence of life. Apparent death is the end of life as indicated by the absence of heartbeat or breathing. Legal death is the total absence of activity of the brain, heart, and lungs, as observed and declared by a physician.

Decay: Disintegration of wood or other substance through the action of fungi.

Decay Heat:  The heat produced by radioactive materials as nuclides spontaneously transform into other
nuclides or into different energy states. Each decay process has a definite half-life.

Decay Rate:  Math function that reflects the declining emissions of a product over time.

Decibel (DB):  A unit of sound measurement. Sound doubles in loudness for every 10 decibels.

Deciduous:  Trees and plants that shed their leaves at the end of the growing season.

Decipol:  A unit of perceived air quality. Air on mountains or the sea has a decipol = 0.01; city air with moderate air pollution has a decipol = 0.05- 0.03; acceptable indoor air quality has decipol = 1.4 (for 80% satisfaction)

Decitex (dtex):  (1) The mass in grams of 10,000 meters of fiber or yarn. (2) A direct yarn numbering system used to define size of fiber or yarn. The higher the number, the coarser (larger) the yarn.

Deciview: A measurement of visibility. One deciview represents the minimal perceptible change in visibility to the human eye.

Deck: An elevated platform. “Deck” is also commonly used to refer to the above-ground floors in multi-level parking garage.

Deck Paint: An enamel with a high degree of resistance to mechanical wear designed for use on such surfaces as porch floors.

Decking:  The wood material installed under roofing material to support the roofing.

Declination of Sun:  The angle of the sun above or below the equatorial plane. This is plus if north of the plane and minus if below and varies day by day throughout the year from +23.47o to June 21 to -23.47o to December 21.

Decomposable Waste:  Waste which, under suitable natural conditions, can be transformed through biological and chemical processes into compounds that do not impair the quality of waters of the State. Incomplete decomposition may result in some water quality degradation (i.e.: hardness, taste, odor, etc.).

Decomposition:   The breakdown of matter by bacteria and fungi.

Decongestant:  Pronunciation (dē′kon-jes′tant).  An agent that possesses this action.

Deconstruction:  A process to carefully dismantle or remove useable materials from structures, as an alternative to demolition. It maximizes the recovery of valuable building materials for reuse and recycling and minimizes the amount of waste land-filled. Deconstruction options may include: Reusing the entire building by remodeling, moving the structure to a new location or taking the building apart to reuse lumber, windows, doors, and other materials.

Decontamination:  The removal of unwanted substances from personnel, rooms, building surfaces, equipment, etc.

Decontamination Factor:  A measure of air cleaning effectiveness; the ratio of the concentration of a
contaminant in the untreated air or gas to the concentration in the treated air or gas.

Decorative: Ornamental; not required for the operation of essential systems and components of a home.

Deep-Well Injection:  Deposition of raw or treated, filtered hazardous waste by pumping it into deep wells, where it is contained in the pores of permeable subsurface rock.

Default Assumptions (used in assignment of dose):  The largest dose contributions attributable to exposure to residual nuclear fallout contamination in the Marshall Islands result from either internal exposure from intakes of radionuclides through ingestion, inhalation and/or absorption through the skin or external exposure from radionuclides distributed in the soil. External exposure rates can be measured directly using instrument surveys of the radiation field. The assignment of dose to internally deposited radionuclides is much more complicated. Biokinectic and dosimetric models developed by the International Commission on Radiological Protection (ICRP) are used to convert whole body burdens (from whole body counting or from in vitro bioassay tests such as urinalysis) into dose. In the case of a chronic exposure, organ and body burdens continue to build up over time until a steady state is reached where losses due to decay and excretion are balanced by intake and absorption. Cesium-137 has an effective half-life in an adult of about 110 days, and under chronic exposure conditions reaches a maximal dose contribution after about 2 years. By contrast, plutonium absorbed from the gastrointestinal or respiratory tract enters the blood stream and deposits in liver and bone with an effective half-life of 20 to 50 years. Only a small fraction of plutonium entering the blood stream is excreted in urine with the long-term excretion rate approaching 2 x 10-5 of the systemic body burden per day. Knowledge of excretion rates and time of exposure are important when interpreting urinalysis data. A more detailed discussion of the dose calculation methodology is given elsewhere (see under Daniels et al., 2005).

Deflect: To bend or deform under weight.

Deflection: The amount of bending movement of any part of a structural member perpendicular to the axis of the member under an applied load.

Deforestation:  The removal of forest cover from an area.

Defrost:  To melt frost; as in from an air conditioner or heat pump coil.

Defrost Cycle:  The process of removing ice or frost buildup from the outdoor coil during the heating season.

Defrost Timer:  A device which shuts unit off the compressor long enough to permit ice and frost accumulation on evaporator to melt.

Degradation:   Chemical or biological breakdown of a complex compound into simpler compounds.

Degrade:  Degradation shall be determined by comparison of the waste field and reference site(s) for characteristic species diversity, population density, contamination, growth anomalies, debility, or supplanting of normal species by undesirable plant and animal species. Degradation occurs if there are significant differences in any of three major biotic groups, namely, demersal fish, benthic invertebrates, or attached algae. Other groups may be evaluated where benthic species are not affected, or are not the only ones affected.

Degreaser:   A chemical such as soap, solvents, alkali, or detergent that dissolves and helps remove greases and oils.

Degree-day:  A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.

Degree Day:  A unit for measuring the extent that the outdoor daily average temperature (the mean of the maximum and minimum daily dry-bulb temperatures) falls below (in the case of heating, see Heating Degree Day), or falls above (in the case of cooling, see Cooling Degree Day) an assumed base temperature, normally taken as 65 degrees Fahrenheit, unless otherwise stated. One degree day is counted for each degree below (for heating) or above (in the case of cooling) the base, for each calendar day on which the temperature goes below or above the base.

Degree Days for Cooling Calculations:  The sum, over a stated period of days, e.g. month, of positive values of the arithmetic difference between a stated reference ‘base temperature’ and the daily mean dry bulb air temperature. The base temperature for assessing cooling requirements is normally set above that used for assessing heating requirements to allow for the fact that acceptable comfort temperatures in summer are higher than those adopted for winter heating assessments.

Degree Days for Heating Calculations:  The product of the number of degrees below a given base temperature and the number of days when that difference occurs. The base temperature is usually defined between 15.5o to 21oC. Different base temperatures are required to estimate heating demands, frost protection, and for relating insulation standards to internal gains.

Degree Hour:  The product of 1 hour, and usually the number of degrees Fahrenheit the hourly mean temperature is above a base point (usually 65 degrees Fahrenheit); used in roughly estimating or measuring the cooling load in cases where processes heat, heat from building occupants, and humidity are relatively unimportant compared to the dry-bulb temperature.

Degree Rankine (°R):  An absolute temperature scale. (°F + 459,67).

Degree Réaumur (°Ré):  An absolute temperature scale. ((°F - 32) x 4/9).

Degree of Intercooling:  Difference in air or gas temperature between the outlet of the intercooler and the inlet of the compressor.

Degree of Saturation:  Is the ratio of weight of vapor existing in a given space to the weight that would be present if the space were saturated at the space temperature.

Degrees Celsius (°C):  An absolute temperature scale. ((°F - 32)x 5/9).

Degrees Fahrenheit (°F):  An absolute temperature scale. ((°C x 9/5) + 32).

Degrees Kelvin (°K):  An absolute temperature scale. The kelvin unit of thermodynamic temperature, is the fraction 1/273,16 of the thermodynamic temperature of the triple point of water. The triple point of water is the equilibrium temperature (0,01 °C or 273,16 K) between pure ice, air free water and water vapour.

De-Humidistat: A control mechanism used to operate a mechanical ventilation system based upon the relative humidity in the home.

Dehumidification: (1.) Condensation of water vapour from air by cooling below the dew point, (2.) removal of water vapour from air by chemical or physical methods.

Dehumidifier:  An air cooler that removes moisture from the air.

Dehumidifier, Surface:  An air conditioning unit, designed primarily for cooling and dehumidifying air through the action of passing the air over wet cooling coils.

Dehumidifying Effect, Air Cooler:   Product of the weight of moisture condensed in the cooler by the constant 1060.

Dehydration: (1.) Removal of water vapour form air by the use of absorbing or adsorbing materials, (2.) removal of water from stored goods.

Dehydrator:  A device used to dry refrigerant. 

Dehydrator-Receiver:  A liquid refrigerant receiver that also contains a desiccant to remove moisture.

Deice Control:  Device for operating a refrigerating system in such a way as to provide melting of the accumulated ice and frost.

Deionized Water:  Water that goes through an ion exchange process in which all positive and negative ions are removed.

Deliquescent:  Melting and becoming a liquid by absorbing moisture.

Deliquescence:  A solid absorption agent used in deliquescent type dryers.

Delisted Species:  Species that are removed from the endangered species list either because it is no longer endangered or threatened, or because it has gone extinct.

Delta P:  Describes the pressure drop through a component and is the difference in pressure between two points.

Delta T:  A term indicating a temperature relationship between two temperatures or temperature variation between two points.

Delta Transformer:  Three-phase electrical transformer wired in the delta configuration, this is also forms a triangle.

Demand:  Flow of air under specific conditions required at a particular point.

Demand Control:  A device that controls the kW demand level by shedding loads when the kW demand exceeds a predetermined set point.

Demand Controlled Ventilation:  A system having sensor-driven control units that turn on ventilation systems when gas concentrations (e.g., carbon dioxide) exceed a preset level.

Demand for Energy:  The peak need for electrical energy. Some utilities levy a monthly charge for demand.
Demand Meter:  A instrument that measures the kilowatt-hour usage of a circuit.

Demand Respirator:  A respirator where the pressure in the facepiece is negative with respect to the ambient pressure during inhalation and positive during exhalation; refer to CSA Z94.4 for the definition.

Demand Side Management (DSM):  The planning and implementation of strategies designed to encourage consumers to improve energy efficiency, reduce energy costs, change the time of usage, or promote the use of different energy source.

Demand-Side Waste Management:  Process whereby consumers use purchasing decisions to communicate to product manufacturers that they prefer environmentally sound products packaged with the least amount of waste, made from recycled or recyclable materials, and containing no hazardous substances.

Demand (tankless) Water Heater:  A type of water heater that has no storage tank thus eliminating storage tank stand-by losses. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed.

Dematerialization:  The reduction of the size of products, particularly as a way to conserve mineral resources.

Demeanor:  Demeanor refers to a person’s bearing, or behavior towards others.

Demister:  A device designed to collect and divert moisture away from downstream filters (i.e., prefilters, HEPAs, and adsorbers). Demisters are installed in final filter plenums upstream of the first stage HEPA filters to prevent water damage to the filters.

Demolition:  The wrecking or removal of any load-supporting structural member of a building or structure.

Demonstrator:  A vacuum that has been out of the original box for display purposes and may have been shown in a professional demonstration.  Considered to be in new condition but not sold as new.  

Demulsibility:  The ability of a fluid that is insoluble in water to separate from water with which it may be mixed in the form of an emulsion.

Denier:   A unit of fineness for fibers based on a standard of 50 milligrams per 450 meters of fiber.

Density:  Is the weight of a given volume of gas, usually expressed in lb / cu ft at SPT condition.

Deodorizer:  A device that absorbs odors, usually by principle of 
absorption.

Deoxyribonucleic Acid (DNA):  A nucleic acid that is bound in double helical chains by hydrogen bonds between bases, forming the basic material in the chromosomes of the cell nucleus; it contains the genetic code and transmits the heredity pattern.

Department:  The New York State Department of Labor.

Depleted Uranium:  Uranium having a lower proportion of the isotope uranium-238 than is found in naturally occurring uranium. The masses of the three uranium isotopes with atomic weights 238, 235, and 234 occur in depleted uranium in the weight-percentages 99.8, 0.2, and 5 × 10–4, respectively. Depleted uranium is sometimes referred to as D-38 or DU.

Deposit Control Additives: Substances added to motor vehicle fuel to reduce and prevent deposits in the fuel delivery system and engine intake valves.

Deposition:  The laying down of material from erosion and transported by water or air.

Depressurization:   A condition that occurs when air pressure inside a structure is lower than air pressure outside.

Depressurize:  Cause to have a lower pressure or vacuum with respect to a reference of a higher pressure.

Depth Filter:  A filter medium that retains contaminants primarily within tortuous passages.

Depth Filtration:  A process that entraps contaminants both within the matrix and on the surface of the filter media.

Der p I:   A purified mite allergen from Dermatophagoides pteronyssinus, a species of mite commonly found in house dust accumulations and thought to be a contributory cause of atopic house dust asthma.

Derived Concentration Guide (DCG):  Concentrations of radionuclides in water and air that could be continuously consumed or inhaled for one year and not exceed the DOE primary radiation standard to the public (100 mrem/y EDE).

Dermal Exposure:  Contact between a microorganism (or chemical) and the skin.

Dermatitis:  Pronunciation (der′mă-tī′tis, -tit′i-dēz).  Inflammation of the skin.
[derm- + G. -itis, inflammation].

Dermatophytes:  A fungus that causes skin disease in humans or other animals.
Dermatosis:  A broader term than dermatitis; it includes any cutaneous abnormality, thus encompassing folliculitis, acne, pigmentary changes, and nodules and tumors.

Desalination:  Production of fresh (potable) water from sea water, salt or brackish water by one of several processes, e.g. distillation, flash distillation, electrodialysis or reverse osmosis if salt content is not too huge.

Describe: Report in writing on a system or component by its type or other observed characteristics to distinguish it from other components used for the same purpose.

Descriptive Scale:  A subjective scale in which the subject is asked to choose between a given list of descriptions in casting a comfort vote.

Desensitization:  Pronunciation (dē-sen′si-ti-zā′shŭn).  (1.) The reduction or abolition of allergic sensitivity or reactions to the specific antigen (allergen). Syn: antianaphylaxis.  (2.)  The act of removing an emotional complex.  Syn: hyposensitization.

Desertification:  The spread of desert-like conditions due to human exploitation and misuse of the land.

Design Basis Accident (DBA):  The most serious accident that can be hypothesized from an adverse
combination of equipment malfunction, operating errors, and other unforeseen causes.

Design Charrette:  The charrette process is focused workshop(s) which take place in the early phase of the design process. All project team members meet together to exchange ideas, encouraging generation of integrated design solutions.

Design Heat Losses:  A term expressing the total predicted envelope losses over the heating season for a particular house design in a particular climate.

Design for Environment:  An engineering perspective in which the environmentally related characteristics of a product, process, or facility design are optimized.

Design Pressure:  The maximum continuous operating pressure as designed by the manufacturer.

Design Temperature:  A high or low temperature used for designing heating and cooling systems.
Design Value: The pollutant concentration used by air quality managers as the basis for determining attainment of an air quality standard, generally by using an air quality model. The design value may or may not be the same as the designation value.

Designated Waste:  Non-hazardous waste that consists of or contains pollutants which, under ambient environmental conditions at the waste management unit, could be released at concentrations in excess of applicable water quality objectives, or which could cause degradation of waters of the state. Also applies to hazardous waste that has been granted a variance from hazardous waste management requirements.

Designation Value: The pollutant concentration used by air quality managers for designating attainment status of an air district with respect to the state and federal ambient air quality standards. Generally, the designation value is the highest concentration that remains after excluding certain qualifying values. For a specific pollutant, the designation value for the state and federal standards may not be the same.

Designer: One who designs houses, interiors, landscaping or other objects. When used it the context of residential construction it usually suggests that a designer is not a licensed architect. Most jurisdictions don’t require an architectural license for most single family construction.

Desorption:  Opposite of absorption or adsorption. In filtration, it relates to the downstream release of particles previously retained by the filter.

Dessicant:   A chemical agent that absorbs moisture.

Desuperheater:  A heat exchanger designed to remove excess superheat from a system. Normally used as a heater for pools or domestic water.

Detergent:   (1.) Synthetic washing agent that helps remove dirt and oil. Some contain compounds that kill bacteria or encourage algae growth.  (2.) A chemical composition that cleans.

Determine: To arrive at an opinion or conclusion pursuant to examination.

Dew Point:  Of a gas is the temperature at which the vapor in a space (at a given pressure) will start to condense (form dew). Dew point of a gas mixture is the temperature at which the highest boiling point constituent will start to condense.

Dew Point Cup:  An apparatus consisting of a small, polished, stainless steel cup placed in a container into which is passed the sample gas. The temperature of the polished surface is lowered by immersing dry ice (solid carbon dioxide) in an acetone solution contained in the cup. The temperature at which fog appears on the cup is the dew point of the sample.

Dewater:  To remove water from wastes, soils or chemicals.

Dewatered Sludge:  Residual semi-solid waste from which a portion of the free liquid has been evaporated or otherwise removed. It is usually 20 percent solids by volume.

Dewatering:  A physical process that removes sufficient water from sludge so that its physical form is changed from essentially that of a fluid to that of a slurry or damp solid.

DFM:  A NIOSH abbreviation which refers to a respirator filter cartridge suitable for use against dusts, fumes, or mist; see particulate.

DFSCEPM:  Director Field Support and Common Equipment Program Management.

DFT: Dry-film thickness usually expressed in thousandths of an inch (mils).

DGCPS:  Director General Construction and Property Services.

DGHS:  Director General Health Services.

DI:   DI distribution integrity; the relationship between the outside air (OA) quantity entering the HVAC equipment and the OA that actually gets delivered to the building occupants.

Di Water:  De-ionized water; water processed through an ion exchange process by passing through a mixed resin bed to remove positive and negative ions. The purity of water is measured by its electric resistance.

Diac:  A two-lead alternating current semiconductor that allows current to flow in both directions at a preset voltage.

Dialysis:  The diffusion of solute molecules through a semi-permeable membrane.

Diaphragm:  A stationary element between stages of a multistage centrifugal compressor. It may include guide vanes for directing the flowing medium to the impeller of the succeeding stage. In conjunction with an adjacent diaphragm, it forms the diffuser surrounding the impeller.

Diaphragm Compressor:  Is a positive displacement reciprocating compressor using a flexible membrane or diaphragm in place of a piston.

Diaphragm Cooling:  A method of removing heat from the flowing medium by circulation of a coolant in passages built into the diaphragm.

Diaphragmatic Breathing: Method of breathing which helps you use the diaphragm correctly so you use less effort and energy to breathe.

Diatomaceous Earth Filtration (D.E.):  A filtration method that uses a medium consisting of microscopic shells of single celled plants known as diatoms.

Diatomite:  Skeletal remains of tiny aquatic plants that lived in the ocean and inland seas millions of years ago.

Die Casting:  Process of molding low-melting-temperature metals in ac­curately shaped metal molds.

Dielectric:  A material which is an electrical insulator or in which an electric field can be sustained with a minimum dissipation of power.

Dielectric Fluid:  Fluid with high electrical resistance.

Diesel Engine: A type of internal combustion engine that uses low-volatility petroleum fuel and fuel injectors and initiates combustion using compression ignition (as opposed to spark ignition that is used with gasoline engines).

Dietitian: A health care professional who specializes in food and nutrition.

Differential:  The difference between the cut-in and cut-out of a control.

Differential Pressure:  See: Pressure Drop.

Differential Pressure Indicator:   An indicator which signals the difference in pressure between any two points of a system or a component.

Diffuse Lighting:  A form of lighting where the light is received from a number of different directions such that a precise shadow is not formed.

Diffuse Solar Radiation:  The component of solar radiation that has been scattered by atmospheric molecules, aerosol particles, and by cloud or other particles. The diffuse radiation is somtimes assumed to be isotropic, that is, equally intense from all points of the sky. Also solar radiation scattered by transmission through diffusing glazing, See diffuse transmission.

Diffuse Transmission:   The type of transmission through a diffusing or translucent glazing or other material. Transmitted radiation that is scattered by interaction with the glazing material.

Diffuser: This is a specialized grille with adjustable vents to direct the airflow from the air conditioner into the room. Some models come with a variety of adjustments some of which can distribute airflow in a particular pattern. An example would the ‘shower’ pattern of cool air.

Diffusers and Grilles:   Components of the ventilation system that distribute and diffuse air to promote air circulation in the occupied space. Diffusers supply air and grilles return air.

Diffusion:  In liquid cake washing, removing the original liquor around the individual particles by mixing with the wash liquor. In air, the particle at a size within one or two orders of magnitude of the gas-flow molecules, moves in Brownian motion and collides with a fiber or other filter media material during its random path of travel.

Diffusion Capacity: A measurement of how much oxygen is carried from your lungs into your bloodstream.

Diffusion, Scattering: Process by which the spatial distribution of a beam of radiation is changed when it is deviated in many directions by a surface or by a medium, without change of frequency of its monochromatic components. (Note: a distinction is made between selective diffusion and non-selective diffusion according to whether or not the diffusion properties vary with the wavelength of the incident radiation.)

Diffusion Test:  A test to determine the integrity of a filter. The test is based upon the transition from diffusional flow to bulk flow of a gas, though a wetted filter.

Diffusional Interception:  In gas filtration, at low gas flow velocities, tiny particles are subject to Brownian motion, enabling them to move out of the gas streamlines and become intercepted by the filter.

Diffusional Flow Test:  To determine the integrity of a filter. The test is based on the measurement of the diffusional flow of a gas through a wetted filter. Either the gas or the downstream liquid, displaced by the gas, may be measured. The transition from diffusional flow to bulk flow (bubble point) can be determined.

Diffusion, Scattering:  Process by which the spatial distribution of a beam of radiation is changed when it is deviated in many directions by a surface or by a medium, without change of frequency of its monochromatic components. (Note: a distinction is made between selective diffusion and non-selective diffusion according to whether or not the diffusion properties vary with the wavelength of the incident radiation.)

Digested Sludge:  Sludge or thickened mixture of water with sewage solids in which the organic matter has been decomposed by anaerobic bacteria.

Digestion:   The biochemical decomposition of organic matter, resulting in partial gasification, liquefaction, and mineralization of pollutants.

Diligence:  Persistent effort in the completion of a specific task, such as the construction of a water diversion structure and placing water to beneficial use.

Diluent - Any liquid or solid material used to dilute or carry an active ingredient.

Dilution:  (a) To thin down or weaken as by mixing with water or other liquid. (b) Disposal of wastewater or treated effluent by discharging it into a stream or body of water.

Dilution Air:   The air required by some combustion heating systems in order to isolate the furnace from outside pressure fluctuations and to maintain an effectively constant chimney draft.

Dilution Device: A draft diverter or barometric draft control on an atmospheric-draft combustion appliance.

Dilution Factor:  The ratio of the quantity of wastewater (untreated, partly treated, or completely treated) effluent to the average quantity of diluting water available at the point of disposal or at any point under consideration; usually expressed in percentage.  Also called available dilution.

Dilution Ventilation:   Dilution of contaminated air with uncontaminated air in a general area, room, or building for the purpose of health hazard or nuisance control.

Dimension Lumber: Yard lumber from 2 inches to, but not including, 5 inches thick and 2 or more inches wide. Includes joists, rafters, studs, plank, and small timbers.

Dimorphic Fungus:  A fungus with the ability to exhibit alternate growth forms, exhibiting yeast-like cells at 98.6oF (37oC), and exhibiting filamentous (mold) growth at room temperature.

Dioctylphthalate (DOP):   A chemical used to thermally generate consistent particles of 0.3 microns in size. The chemical is also a known carcinogen.

Direct Air System:  See “Dirty-Air Design.”

Direct Bioassay:  The measurements of radioactive material in the human body utilizing instrumentation that detects radiation emitted from radioactive material in the body (synonymous with in vivo measurements).

Direct Connect:  Power team canisters that have electric power nozzles require that electricity travel from the canister to the power nozzle. In the past this was accomplished by attaching external cords to the hose and wands. Later, electric hoses were developed that had the electrical wires inside the hose with pigtails on either end. The Direct Connect system now eliminates both external cords on the hoses and wands as well as the pigtails. The electrical system is integrated into the hoses, wands and power nozzle and is automatically connected when the vacuum cleaner is assembled for use.

Direct Current:  Current that travels only in one direction. 

Direct Digital Control (DDC):  Use of a digital computer to perform required automatic control operations.

Direct Expansion:  When the refrigerant is the system is either condensed or evaporated directly by the medium being heated or cooled.

Direct Expansion Systems:  One of two types of basic cooling media (the other is chilled water). Direct expansion systems utilize Freon for cooling and dehumidification. The three most common methods of heat rejection are air cooled, water cooled and glycol cooled.

Direct Fired Heater (DFH):  Direct fired heaters, or bunk heaters, are devices that can reduce idling by providing in-cabin heat for drivers in cold temperatures. Some product models offer an engine heating option that will also keep the engine warm overnight. Most DFHs operate by using fuel directly from the main tractor fuel tank. These devices can generally provide 10 to 20 hours of heat on a single gallon of diesel fuel, depending on the settings and options.

Direct Gain:  The directly transmitted solar radiation absorped within a room.
 
Direct Gain System: Passive solar heating system in which sunlight penetrates and warms the house interior directly.

Direct Glare:   Glare caused by self luminous objects situated in the visual field, especially near the line of sight.

Direct Interception:  Gas filtration: particles larger than the pores are removed by direct contact with the filter surface. Some particles smaller than pores can be removed as well depending on the proportion to their size hitting the surface.

Direct Method of Cooling:   A system in which the evaporator is in direct contact with the material or space refrigerated or is located in air circulation passages communicating with such spaces.

Direct Nailing: To nail perpendicular to the initial surface or to the junction of the pieces joined. Also termed Face Nailing.

Direct Solar Gains: See direct gain.

Direct Solar Radiation:  Solar radiation which reaches the Earth’s surface after selective attenuation by the atmosphere as a collimated beam (i.e. the solar radiation which is not absorbed or diffused).

Direct Sunlight:   Direct solar radiation in the visible wavelengths.

Direct Vent:  Pulls outside air for combustion and vents combustion gases directly outside.

Direct Water Heater:   A type of water heater in which heated water is stored within the tank. Hot water is released from the top of the tank when a hot water faucet is turned. This water is replaced with cold water that flows into the tank and down to just above the bottom plate under which are the burners.

Directional Control Valve:  A valve to control the flow of air in a certain direction.

Directional Lighting:  A form of lighting where light is received from a single direction.

Dirt Holding Capacity:  The quantity of contaminant a filter element can trap and hold before the maximum allowable back pressure or delta P level is reached.

Dirt Sensor/Detective/Finder/Alert:  A laser or light beam that detects particulate or debris passing into the vacuum. 

Dirty-Air Design:  This is another term for “Direct Air” system and is a vacuum cleaner design where the airflow that picks up the soils passes directly through the motor fan before any filtration and then goes into the dustbag. Traditional uprights are most often designed using this system, which is known as a “Dirty Air” system because unfiltered air and soils passed through the motor. This often results in broken fans and other motor damage. Use of attachments in vacuum cleaners using this design is often awkward, requiring specialized adapters.   

Disaster Recovery:  The act or actions associated with returning to normal operations in the wake of a disaster.

Disc:  The movable seating surface in a valve.

Discharge:  (a) As applied to a stream or conduit, the rate of flow, or volume of water flowing in the stream or conduit at a given place and within a given period of time, (b) The passing of water or other liquid through an opening or along a conduit or channel, (c) The rate of flow of water, silt, or other mobile substance which emerges from an opening, pump, or turbine, or passes along a conduit or channel, usually expressed as cubic feet per second, gallons per minute, or million gallons per day.

Discharge Prohibitions:  See Prohibition.

Discharger:  Any person who discharges waste which could affect the quality of California waters, and includes any person who owns a waste management unit or who is responsible for the operation of a waste management unit.

Discomfort:  Discomfort is viewed as a mild form of distress.

Discontinuous Phase:  Separated phase or product from the continuous phase. Example: water maybe the discontinuous phase when separated from hydrocarbon, air or gas.

Disease:   A state in which a function or part of the body is no longer in a healthy condition.

Disinfect:  To destroy harmful bacteria, viruses, etc., in wastewater.

Disinfectants:   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.

Disinfected Wastewater:  Wastewater to which chlorine or other disinfecting agent has been added, during or after treatment, to destroy pathogenic organisms.

Disinfection:   A chemical or physical process that kills pathogenic organisms.

Dissolved Oxygen (DO):  The oxygen dissolved in water, wastewater, or other liquid, usually expressed in milligrams per liter, parts per million, or percent of saturation.
Dismantle: To open, take apart or remove any component, device or piece that would not typically be opened, taken apart or removed by an ordinary occupant.
Dispense:  The final service following eye examination, lens design, frame selection, ordering & verification; fitting fabricated eyewear properly to the face.

Dispersion:  The most general term to define the scattering of particulate matter suspended in air or other gases.

Dispersion Model: See air quality simulation model above.

Displacement:  Volume obtained by multiplying area of cylinder bore by length of piston stroke.

Displacement Compressor:  A machine where a static pressure rise is obtained by allowing successive volumes of gas to be aspirated into and exhausted out of a closed space by means of the displacement of a moving member.

Displacement of a Compressor:  The volume displaced by the compressing element of the first stage per unit of time.

Disposable Filter:  A filter element intended to be discarded and replaced after one service cycle.

Disposal:   Final placement or destruction of wastes.

Disposal System:  A septic tank and drain field for sub-surface disposal of wastewater.

Disposer: A device that grinds food sufficiently to enter drains for disposal without clogging them.

Dissolved Solids:   Disintegrated organic or inorganic material contained in water.

Distillation:  Process of vaporizing a liquid and collecting the vapor, which is then usually condensed into a liquid.

Distilling Apparatus:  Fluid-reclaiming device used to reclaim used refrigerants.

Distortion: Alteration of viewed images caused by variations in glass flatness or in homogeneous portions within the glass. An inherent characteristic of heat-treated glass.

Distress:  Distress is a state associated with invasive procedures conducted on an animal, or with restrictive or other conditions which significantly compromise the welfare of an animal, which may or may not be associated with pain, and where the animal must devote substantial effort or resources to the adaptive response to challenges emanating from the environmental situation.

Distribution System:  This term refers to that part of a central heating system used to deliver heated transfer media to the living space, and return the cooled transfer media to the appliance for re-heating. In a forced air system this includes the blower, ducts, registers, dampers, and cold air returns. In a hot water system this includes circulators, supply lines, radiators, and return lines.

District Heating and Cooling:  Use of a central utility system de­signed to provide heating and cooling to large residential and industrial areas.

Disturbance:  Any activities that disrupt the matrix of ACM or PACM, or generate debris, visible emissions or airborne asbestos fibers from ACM or PACM. This includes moving of friable asbestos containing material from one place to another.

Diuretic: Medication that increases urine output. Helps the body get rid of excess fluid. Also called a “water pill.”

Diurnal Rhythm:  Most animals (and plants) have a daily rhythm of activity. This is the diurnal rhythm.

Diverter: Valves which have a single inlet and direct water to one of two outlets. Diverters are used with handshowers, shower risers, tub & shower combinations, and kitchen faucet sprayers.

Diverter Valve: A device that changes the direction of water flow from one faucet to another.

DMF:  Drug Master File. A written document that explains the formulation of an active ingredient, referenced in an Investigational New Drug (IND), New Drug Application (NDA), or Amendment to New Drug Application (ANDA) from a company.

DNBCD:  Director Nuclear, Biological and Chemical Defense.

DOE:  Department of Energy.

Doe-2:  A public domain computer program for energy analysis developed by Lawrence Berkeley National Laboratory. Well-suited for large commercial buildings, the program calculates a building’s energy use and life-cycle costs based on its location, construction, operation and HVAC systems. It is useful in evaluating building system design, energy budgets, life-cycle costs and benefits, and can explore trade-offs between design alternatives. It includes four main calculation sections: loads, systems, plants and
economics.

DOH:  Department of Health (NY).

DOL:  The Department of Labor, of which OSHA is a part.

Dolly Varden Siding: Beveled wood siding which is rabbeted on the bottom edge.
Domestic Hot Water (DHW):  Refers to a separate, closed system to heat potable (drinkable) water and supply it to the dwelling unit for washing, bathing, etc.

Doorjamb (Interior): The surrounding case into which and out of which a door closes and opens. It consists of two upright pieces, called side jambs, and a horizontal head jamb.

DOP:  Dioctylphthalate, an aerosol medium used as a challenge for efficiency and leak testing of hepa filters.

Doppler Equipment:  A Doppler transducer is one that uses ultrasound to evaluate blood flow inside the body. The instrument looks like a microphone, and sends and receives silent, high frequency sound waves.

Dormant:  Unexercised, not active, but capable of becoming exercised.

Dormer:  A vertical window projecting from a roof.

Dose: The amount of a pollutant that is absorbed. A level of exposure which is a function of a pollutant’s concentration, the length of time a subject is exposed, and the amount of the pollutant that is absorbed. The concentration of the pollutant and the length of time that the subject is exposed to that pollutant determine dose.

Dose commitment:  Dose that an organ or tissue would receive during a specified period of time (e.g., 50 or 70 years) as a result of one year’s intake of one or more radionuclides.

Dose Equivalent:  Product of absorbed dose in rad (or gray) in tissue and a quality factor representing the relative damage caused to living tissue by different kinds of radiation, and perhaps other modifying factors representing the distribution of radiation, etc. expressed in units of rem or sievert (l rem = 0.01 sievert).

Dose-Response: The relationship between the dose of a pollutant and the response (or effect) it produces on a biological system.

Dose-Response Relationship:  Correlation between the amount of exposure to an agent or toxic chemical and the resulting effect on the body.

Dosimeter:  Portable detection device for measuring the total accumulated exposure to ionizing radiation.

Dosimetry:  Theory and application of the principles and techniques of measuring and recording radiation doses.

DOT:  Department of Transport (USA).

Double Acting Compressor:  A positive displacement type compressor.

Double-blind Study:   A type of clinical trial study design in which the study participants and the investigators do not know the identity of the interventions (or lack of interventions) until data collection has been completed.

Double-Glazing: In general, any use of two lights of glass, separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In insulating glass units, the air between the glass sheets is thoroughly dried and the space is sealed, eliminating possible condensation and providing superior insulating properties.

Double Bag: Features a conventional bag on a cage and an inner bag that filters from inside out, with the bottom open for dirty air entrance. Puts more, but not necessarily effective, cloth area in a given size baghouse.

Double Coverage: Application of asphalt roofing so that the lapped portion is at least 2 inches wider than the exposed portion, resulting in two layers of roofing material over the deck.

Double Duty Case:  Commercial refrigerator in which a part of space is for refrigerated storage and part is equipped with glass windows for display purposes.

Double Hung Window: A window with sashes that slide vertically and allow opening from the top and bottom.

Double Layer Fabric: By joining a fine filter layer with an open, coarser layer of mesh, these fabrics combine high flow capacity and fine particle capture efficiency with the extremely durable construction needed for large-scale process filtration.

Double Plate: When two layers of 2x4s are placed on top of studs in framing a wall.

Double Strength: In float glass, approximately 1/8” (3 mm.) thick.

Double Tree: Refers usually to a precast roof deck panel poured with two fins in its underside to impart flexural rigidity.

Down Gradient:  The direction in which groundwater flows.

Down Stream:  In the direction of the current of a stream.

Down Stream Ocean Waters:  Waters downstream with respect to ocean currents.

Downflow Furnace:  A furnace that intakes air at its top and discharges air at its bottom.

Downgradient:  In the direction of groundwater flow from a designated area; analogous to downstream.

Downspout: The pipe that carries water down from the gutter or scupper. Also called a leader.

Downstream:  The portion of the flow stream which has already passed through the system or the portion of the system located after a filter or separator/filter.

Downstream Impacts:  Environmental impacts caused by consumer use and product disposal.

Downstream Side of Filter:  The filtrate or product stream side of the filter. Fluid and/or solids that have passed through the filter.

Downtime:  The period of time when a computer or system is shut down and is considered non-operational.

DPI (dry powder inhaler): This is a variety of devices that provide a new way of taking inhaled medicine. The propellants used in regular-metered dose inhalers can be bad for the environment. For this reason, drug companies are in the process of switching over to DPI’s, which do not use a propellant at all. The medicine is in the form of a very fine powder that is easily inhaled without the use of an aerosol spray device. DPI’s can be easier to use, because the patient doesn’t have to coordinate the timing of activating the inhaler and breathing in, and the problems of bad taste and unpleasant “feel” are also greatly reduced.

DPMA:  Data Processing Managers Association. A national trade association similar to AFCOM.

Draft:   A column of burning combustion gases that are so hot and strong that the heat is lost up the chimney before it can be transferred to the house. A draft brings air to the fire to help keep it burning.

Draft Diverter:   A door-like device located at the mouth of a fireplace chimney flue for controlling the direction and flow of the draft in the fireplace as well as the amount of oxygen that the fire receives.

Draft Gauge:  An instrument used to measure the draft in an appliance.

Draft Hood:   A device built into or installed above a combustion appliance to assure the escape of combustion byproducts, to prevent backdrafting of the appliance, or to neutralize the effects of the stack action of the chimney or vent on the operation of the appliance.

Draft Regulator: Device which maintains a desired draft in a combustion-heated appliance by automatically controlling the chimney draft to the desired value.

Drag:  Occurs when a valve does not close completely after popping and remains partly open until the pressure is further reduced.

Drain pan: Also known as the condensate pan, this is a pan positioned at the bottom of the air handling unit underneath the evaporator coils. As the name suggests, it collects the condensate that drips from the evaporator coils. This is then drained out through a drainpipe or, as is the case with some portable units, is removed and emptied.

Drain Tile Loop:A continuous length of drain tile or perforated pipe extending around all or part of the internal or external perimeter of a basement or crawlspace footing.

Drain Trap: A dip in the drain pipe of sinks, toilets, floor drains, etc., which is designed to stay filled with water, thereby preventing sewer gases from escaping into the room.

Drain Valve:  A device designed to remove surplus liquid from the compressed air system. Manual units range from petcock to a ball, gate or globe valve. Mechanical types consist of ball float. Electrical drains include solenoid type that is energized by a timer signal, or electric motor driven units. Also pneumatically activated drains.

Drainage Retention Basin (now Lake Haussmann):  Man-made, lined pond used to capture storm water runoff and treated water at the Livermore site.

Draught:  Air movement causing potential discomfort. 

Draw: The amount of progress billings on a contract that is currently available to a contractor under a contract with a fixed payment schedule.

Drawing Detail: A top view drawing of a building or roof showing the roof perimeter and indicating the projections and roof mounted equipment, drawn to scale.

Drawing Outline: A top view drawing of a building or roof showing only the perimeter drawn to scale.

Dredged Material:  Any material excavated or dredged from the navigable waters of the United States, including material otherwise referred to as “spoil.”

Dredging:  The removal of material from the bottom of water bodies using a scooping, scraping, or suction machine.

Dressed and Matched (Tongued & Grooved): Boards or planks machined in such a manner that there is a groove on one edge and a corresponding tongue on the other.

Dressed Size Lumber: The dimension of lumber after shrinking from green dimension and after machining to size or pattern.

Drier:  A device used in a refrigerant line to remove moisture.

Drier Paint: Usually oil-soluble soaps of such metals as lead manganese or cobalt which, in small proportions, hasten the oxidation and hardening (drying) of the drying oils in paints.

Drill Aerosols:  In a dental office there are a number of sources of bacterial aerosols that may transmit disease to staff and patients. These include high speed drilling as well as ultrasonic scaling.   

Drill Hole Casings: The drilling hole is fitted with a series of tubes, or casings, to prevent the collapse of the hole and contamination of the petroleum from falling dirt. Similarly, the casings prevent the contamination of the surrounding soil and water from the extraction process. These casings also guide a special mud made up of clay, water and some chemicals down the shaft to the drill bit. This mud lubricates and keeps the bit cool, as well as moves rock debris from the drilling process up the shaft and out of the way. It also prevents the oil and gas from escaping out of the hole and into the atmosphere when the reservoir is finally reached.

Drip Cap: A molding placed on the exterior top side of a door or window frame to cause water to drip beyond the outside of the frame.

Drip Edge: A device designed to prevent water from running back or under an overhang.

Drip Irrigation: Tubal, flexible hose that is installed within a topsoil layer to deliver water directly to the roots of the plants without water loss due to evaporation or over watering of non-planted areas that can occur with spray-type sprinklers.

Dripleg:  Is a pipe extending downward from the bottom of the airline to collect any condensation flow in the pipe.

Drippage: Bitumen material that drips through roof deck joints, or over the edge of a roof deck.

Drive:  A coupling between the compressor and the engine or motor. The three types of drives most common are; flange mounted motor, V belt drive or direct coupling.

DRJ:  Disaster Recovery Journal. A professional journal specializing in business continuity issues.  (www.drj.com)

Drop Siding: Usually ¾ inch thick and 6 and 8 inches wide with tongued-and-grooved or shiplap edges. Often used as siding without sheathing in secondary buildings.

Dropleg:  Is a pipe coming from the top of the airline to feed air to an outlet for tools or air operated devices, so that condensation does not easily flow into the dropleg.

Droplet Nuclei: Microscopic particles (1-5 microns in size) that can become airborne
when a person coughs, sneezes, shouts, sings, breathes, or talks. Droplet nuclei
produced by a person who has TB disease of the lungs or larynx in an infectious
state can remain airborne for a long time and can spread TB to others.

Dropping a Stringer: In carpentry, “dropping” a stringer refers to cutting short on the bottom of a stairs to allow for thickness of the first tread.

Drug Allergy:  Sensitivity (hypersensitivity) to a drug or other chemical.

Dry-In: To make a building waterproof.

Dry Adiabatic Lapse Rate:  Rate at which unsaturated air cools as it travels vertically, provided that all temperature change is adiabatic (without heat exchange), and no condensation occurs.

Dry Bulb Temperature:  Is the ambient gas temperature as indicated by a standard thermometer.

Dry Bulb Thermometer:  An instrument that measures air temperature independently of humidity.

Dry Capacitor Condenser:  Electrical device made of dry metal and dry insulation; used to store an electrical charge.

Dry Cell Battery:  A battery, having no liquid in the cell.

Dry Collector: Dust collectors that use mechanical means (centrifugal force, impingement, filtration) to remove particulate matter from exhaust gas, such as expansion chambers, knockout boxes, centrifugal collectors, cartridge filters and baghouses. Devices not using H2O.

Dry Gas:  Is any gas or gas mixture that contains no water vapor and/or in which all of the constituents are substantially above their respective saturated vapor pressures at the existing temperature.

Dry Glazing: Also called compression glazing, a term used to describe various means of sealing monolithic and insulating glass in the supporting framing system with synthetic rubber and other elastomeric gasket materials.
Dry Heat Sterilization:  Sterilization at or above 356ºF using a convection or forced air oven without moisture; may concurrently de-pyrogenate if adequate time and elevated temperature are employed.

Dry Ice:  Refrigerating substance made of solid carbon dioxide which changes directly from a solid to a gas (sublimates).

Dry Pipe:  A water sprinkler system where the pipe is pressurized with air and not water. This prevents system leaks from immediately discharging water in sensitive environments.

Dry Rot: See Fungal Wood Rot.

Dry Scrubber:  A chemical reaction chamber that neutralizes acids in a gas stream. Two system types: the spray dryer system injects a slurry, whereas dry sorbent injection systems use a dry powder.

Dry Seal: Accomplishment of weather seal between glass and sash by use of strips or gaskets of Neoprene, EPDM, silicone or other flexible material. A dry seal may not be completely watertight.

Dry Sheet: A ply mechanically attached to wood or gypsum decks to prevent asphalt or pitch from penetrating the deck and leaking into the building below.

Dry System:  Refrigeration system which has the evaporator liquid refrigerant mainly in the atomized or droplet condition.

Dry Unit (Oil Free):  One in which there is no liquid injection and/or liquid circulation for evaporative cooling or sealing.

Drywall:  Gypsum interior wallboard used to produce a smooth and level interior wall surface and to resist fire. Also called gypsum wall board or sheetrock.

Drywall Construction: A type of construction in which the interior wall finish is applied in a dry condition, generally in the form of sheet materials or wood paneling as contrasted to plaster.

Drywall Hammer: A special hammer used for nailing up gypsum board. Also known as an ax or hatchet. Edges should be smooth and the corners rounded off. The head has a convex round and checkered head.

Drywall Nail: Nails used for hanging regular drywall that is to be taped and finished later must have adequate holding power and a head design that does not cut the face paper. They must also be of the proper depth to provide exactly 1 inch penetration into the framing member. Nails commonly used are chemically-etched and are designed with a cupped head.

DSCFM (Dry Standard Cubic Feet per Minute): See gas flow rate.

DSSPM:  Director Soldier Systems Program Management.

Dual Chamber Test Method:  Measures near-field shielding effectiveness by indicating the signal attenuation caused by passage through a test material.

Dual Compressors:  An outdoor unit featuring two compressors, one for everyday cooling and a second larger one for extreme temperature days. Provides superior durability designed for cost-saving efficiency and low sound levels.

Dual Duct System:    An air conditioning system that has two ducts, one is heated and the other is cooled, so that air of the correct temperature is provided by mixing varying amounts of air from each duct.

Dual Fuel:  A comfort system that pairs an electric heat pump with a gas furnace, providing an energy-efficient alternative to the conventional furnace/air conditioner combination.

Duct:  Round or rectangular conduit through which air is carried from a central air conditioning system to various locations in a building.

Duct Blower:  A blower-door-like device used for testing duct leakiness and air flow.
Duct Fan:   HVAC term for an axial flow fan mounted in a section of duct to move conditioned air.

Duct Silencer: Insulated section of ductwork connected to the outlet of a fan to attenuate sound. Silencers are available in various sizes and are designed to achieve the desired level of noise reduction.

Ductwork: This can basically be described as a large pipe that carries airflow throughout the building both to and from rooms. These can be used for both heating and cooling. Ductwork is commonly made of metal but flexible ductwork, known as mini-duct, is now also available.

Due-On-Sale: A clause in a mortgage contract requiring the borrower to pay the entire outstanding balance upon sale or transfer of the property.

Dumbwaiter: An elevator with a maximum footage of not more than 9 sq. ft. floor area; not more than 4” headroom and a maximum capacity of 500 lbs. used for carrying materials only.
Duplex:  Any structure which consists of two separate dwelling units in one building.

Duplex Filter: Assembly of two filters with a valve for selection of either or both filters.

Dura Board, Dura Rock: A panel made out of concrete and fiberglass usually used as a ceramic tile backing material. Commonly used on bathtub decks. Sometimes called Wonder Board.

Durable Power of Attorney for Health Care: A legal document that authorizes another person to make health-care decisions for you if you became physically or mentally unable to make these decisions yourself.

Durometer (Shore):  Measure of hardness. Must be defined as being either A or D scale.

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

Dust Cake:  A layer of dust built up on an air filter.

Dust Collection:  A term usually associated with an assembly of large pleated elements that collect air-borne particles where large volumes of air flow is found e.g. granaries, cement factories, abrasive production and other manufacturing facilities.

Dust Collector: An air-cleaning device used to remove heavy particulate loadings from exhaust systems prior to discharge.

Dust Collector, Cyclone: A mechanical device that utilizes the centrifugal force of the inlet gas to remove large particulate matter suspended in the gas.

Dust Collector Efficiency: See Collecting Efficiency.

Dust Holding Capacity:  The amount of atmospheric dust which a filter will capture.

Dust Mask:  See filtering facepiece.

Dust Mites:  Dust mites are microscopic, eight-legged creatures that are 250-300 micrometers in length (7,000 can fit on a fingernail) and are invisible to the naked eye.
Dust mites live on dead human skin cells, (which comprise up to 80% of house dust) as well as fungi and bacteria. They also live off water vapor, which humans provide for them by perspiration and respiration, emitting approximately one pint of moisture per person per night. This is why mites are found even in areas of extremely low humidity and prevention strategies such as reducing humidity levels in the home are generally ineffective. Dust mite feces contains a potent allergen thought to be responsible for as much as 25% of all allergies worldwide.  Physician organizations such as the American Academy of Allergy Asthma and Immunology (AAAAI) state that dust mite feces are a major source of allergen found in house dust. It is clear that dust mite feces is one of the most important and hazardous allergens found in indoor environments.   

Dust Mite Debris:  Dust Mites are probably the closest thing to “bed bugs” that you'll find - if you have a microscope, that is. Invisible to the naked eye, dust mites are tiny creatures closely related to spiders & ticks. The dust mite's favorite food is the dead skin that constantly falls off of our bodies, and they prefer to live where the food is - in our beds, a comfy chair, or our favorite stuffed animals. As dust mites grow, they shed their skin, and just like every other creature in the world, they poop. Dust mite debris is just a combination of shed skin and feces. Every time you hop in bed, this debris makes its way into the air, and that's where it becomes troublesome to humans.  Dust mite debris is second only to pollen in causing allergic reactions. Like other allergens, dust mite debris can trigger an immune system response which leads to symptoms such as sneezing, runny nose, and itchy-watering eyes.  Dust mite debris is removed by Nordic Pure’s MERV 12, electrostatically charged, pleat design air filters.

Dust Mite Feces:  Dust mite feces contains two highly potent allergens Dermatophagoides pteronyssinus and Dermatophagoides farinae generally referred to as Der p1 & Der f1. A dust mite will produce 20 to 100 fecal pellets per day or 200 times its own body weight in feces during its short lifetime. If dust mite pellets were the size of golf balls, the average queen size bed would have a pile of pellets 70 feet high. A female dust mite will also lay 100 eggs during its approximately ten-week lifetime, with a new generation being produced about every three weeks.  During the night, most people toss and turn up to 60 or 70 times. This expels dust mite feces into the air from bedding and pillows. These allergens can then stay in the air for up to two hours. Once airborne, these potent allergens are inhaled where they can cause allergic illness in the first place and stimulate allergic reactions and asthma attacks in those that already have developed allergic disease.  Other activities such as walking, vacuuming (with typical vacuum cleaners) and changing bed linens easily stir up dust mite allergens.

Dust Permeability: The mass of dust (grains) per square foot of media divided by the resistance (pressure drop) in inches of water gauge (WG) per unit of filtering velocity, feet per minute (fpm). Not to be compared with cloth permeability.

Dust Spot Efficiency:   See atmospheric dust spot efficiency test.

Dustbag Change Indicator:  A display on a vacuum cleaner that informs the user that the dustbag needs changing. Given that a full dustbag can decrease cleaning ability and put unnecessary strain on the vacuum motor, this is an excellent feature. Also referred to as “Dustbag Indicator” or “Full Bag Indicator.”

DUSTCHEK:  A filter collection bag used in conjunction with a standard vacuum cleaner to collect dust samples to be analyzed for microbial contamination or allergens.

Dutch Weave:  Warp and weft wire diameters are different in size and the weft wires are closer together to provide excellent strength and high density.

Duty Cycle:  Percentage of time a compressor unit can operate at full load over a thirty minute period.

Dwelling Unit:  A house, including a stationary mobile home, an apartment, a group of rooms, or a single room occupied as separate living quarters.

Dwdi: Double-width, double-inlet fans.

DWV (Drainage, Waste & Vent): The pipes in a plumbing system that remove waste water.

DX:  Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.

DX Coil:  A direct expansion coil. The refrigerant liquid turns to vapor in the coil, cooling the air (or water) flowing across the coil.

Dyeing:  The process of adding color to textiles in fiber, yarn or fabric form.

Dynamic Balance: The mechanical balancing of a rotating part or assembly in motion.

Dynamic Environmental Chamber:  Well-controlled system (including temperature, relative humidity (RH) and air quality/purity) that utilizes realistic air flows for the assessment of chemical emissions from products and materials.

Dynamic Insertion Loss: A reduction of airborne noise levels affected by the installation of an acoustical silencer.

Dynamic Losses:  Friction against duct walls, internal friction in the air mass and direction variations will cause a speed reduction and are therefore called dynamic losses.

Dynamic Type Compressors:  Machines in which air or gas is compressed by the mechanical action of rotating vanes or impellers imparting velocity and pressure to the flowing medium. (Raise the pressure of the air by converting the energy from the velocity of the air to pressure.)

Dynamic Viscosity (Dynamic):  The force in newton required to move a fluid layer of one square meter area and a thickness of one meter with a velocity of one meter per second.

Dyne: The amount of force that cause a mass of one gram to alter its speed by one centimeter per second for each second during which the force acts.

Dyspnea: Difficult breathing.