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For this document, certain terms are defined in this section. Terms not defined herein should have their ordinary meaning within the context of their use. (Ordinary meaning is as defined in "Webster's Ninth New Collegiate Dictionary.")

Backdrafting: A condition where the normal movement of combustion products up a flue, resulting from the buoyant forces on the hot gases, is reversed, so that the combustion products can enter the house. Backdrafting of combustion appliances (such as fireplaces and furnaces) can occur when depressurization in the house overwhelms the buoyant force on the hot gases. Backdrafting can also be caused by high air pressures or blockage at the chimney or flue termination.

Backer Rod: A semi-rigid foam material resembling a rope of various diameters. Used to fill around pipes, etc. to assist in making a sealed penetration. For example, where a pipe is inserted through a concrete slab, a length of backer rod is jammed into the opening around the pipe. Caulking is then applied to the space above the backer rod and between the outside of the pipe and the slab opening. The purpose of the backer rod is to hold the semi-fluid caulk in place until it sets or hardens.

Block Wall Depressurization: A radon mitigation technique that depressurizes the void network within a block wall foundation by drawing air from inside the wall and venting it to the outside.

Perimeter Channel Drain: A means for collecting water in a basement by means of a large gap or channel between the concrete floor and the wall. Collected water may flow to aggregate beneath the slot ("French Drain") or to a sump where it can be drained or pumped away.

Certified: A rating applied by some jurisdictions to individuals or firms that are qualified and authorized to provide radon testing or mitigation services within the area of their jurisdiction.

Client: The person, persons, or company that contracts with a radon mitigation contractor to install a radon reduction system in a building.

Combination Foundations: Buildings constructed with more than one foundation type, e.g., basement/crawlspace or basement/slab-on-grade.

Communication Test: A diagnostic test designed to qualitatively measure the ability of a suction field and air flow to extend through the material beneath a concrete slab floor and thus evaluate the potential effectiveness of a sub-slab depressurization system. This qualitative test is commonly conducted by applying suction on a centrally located hole drilled through the concrete slab and simultaneously observing the movement of smoke downward into small holes drilled in the slab at locations separated from the central suction hole. (See also "Pressure Field Extension")

Contractor An individual listed in EPA's RPP program, specifically one listed as a "Mitigation Service Provider," or certified by a state which requires adherence to the RMS.

Crawlspace Depressurization: A radon control technique designed to achieve lower air pressure in the crawlspace relative to indoor air pressure by use of a fan-powered vent drawing air from within the crawlspace. (See also  Mechanically Ventilated Crawlspace System.)

Diagnostic Tests: Procedures used to identify or characterize conditions within buildings that may contribute to radon entry or elevated radon levels or may provide information regarding the performance of a mitigation system.

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.

Mitigation System: Any system or steps designed to reduce radon concentrations in the indoor air of a building.

Mechanically Ventilated Crawlspace System: A radon control technique designed to increase ventilation within a crawlspace, achieve higher air pressure in the crawlspace relative to air pressure in the soil beneath the crawlspace, or achieve lower air pressure in the crawlspace relative to air pressure in the living spaces, by use of a fan. (See also  "Crawlspace Depressurization".)

pCi/L: The abbreviation for picocuries per liter which is a unit of measure for the amount of radioactivity in a liter of air. The prefix "pico" means a multiplication factor of 1 trillionth. A Curie is a commonly used measurement of radioactivity.

Pressure Field Extension: The distance that a pressure change is induced in the sub-slab area, measured from a single or multiple suction points. (See also “Communication Test”)

Radon: A naturally occurring radioactive element (Rn-222) which exists as a gas and is measured in picocuries per liter (pCi/L).

Radon Decay Products: The four short-lived radioactive elements (Po-218, Pb-214, Bi-214, Po-214) which exist as solids and immediately follow Rn-222 in the decay chain. They are measured in working levels (WL).

Re-Entrainment: The unintended re-entry into a building of radon that is being exhausted from the vent of a radon mitigation system.

Soil Gas: The gas mixture present in soil which may contain radon.

Soil-Gas Retarder: A continuous membrane or other comparable material used to retard the flow of soil gases into a building.

Stack Effect: The overall upward movement of air inside a building that results from heated air rising and escaping through openings in the building envelope, thus causing indoor air pressure in the lower portions of a building to be lower than the pressure in the soil beneath or surrounding the building foundation.

Sub-Membrane Depressurization: A radon control technique designed to achieve lower air pressure in the space under a soilgas retarder membrane laid on the crawl- space floor, relative to air pressure in the crawlspace, by use of a fan-powered vent drawing air from beneath the membrane.

Sub-Slab Depressurization (Active): A radon control technique designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a fan-powered vent drawing air from beneath the concrete slab.

Sub-Slab Depressurization (Passive): A radon control technique designed to achieve lower sub-slab air pressure relative to indoor air pressure by use of a vent pipe (without a fan) routed through the conditioned space of a building and connecting the sub-slab area to the outdoor air. This system relies primarily on the convective flow of warmed air upward in the vent to draw air from beneath the concrete slab.

Working Level (WL): A unit of radon decay product exposure rate. Numerically, any combination of short-lived radon decay products in one liter of air that will result in the ultimate emission of 130,000 MeV of potential alpha energy. This number was chosen because it is approximately the total alpha energy released from the short-lived decay products in equilibrium with 100 pCi of Rn-222 per liter of air. (See also the referenced document in paragraph 8.15.)

Working Level Month (WLM): A unit of exposure used to express the accumulated human exposure to radon decay products. It is calculated by multiplying the average working level to which a person has been exposed by the number of hours exposed and dividing the product by 170.

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