Radon glossary

This glossary holds the radon terms you meet on a test report, a quote or a device label. Each definition carries its source: Health Canada’s measurement guide or guideline page, the 2024 Cross-Canada Radon Survey, the CAN/CGSB-149.11-2024 and 149.12-2024 standards, or the CARST real estate screening guideline. It uses Health Canada’s current terms and names the older ones.

A becquerel is one radioactive decay a second. For radon, that is one atom breaking down and giving off one alpha particle. Bq/m³ counts those decays in one cubic metre of air.

Units and measurement

Average annual radon level

The average radon level in a home, calculated over a twelve-month period.

Becquerel (Bq)

The SI unit of radioactivity. One becquerel corresponds to one nuclear decay per second. For radon gas, one Bq represents one nuclear decay of radon, emitting one alpha particle per second.

Becquerel per cubic metre (Bq/m³)

The unit used to express the concentration of radon in air. Indoor radon measurements in Canada are normally reported in Bq/m³.

Geometric mean

A type of average commonly used when reporting radon concentrations because radon measurements can span a wide range. The 2024 Cross-Canada Survey reports Canadian residential radon results using geometric averages.

Picocurie per litre (pCi/L)

An alternative unit commonly encountered in U.S. radon information. 1 pCi/L = 37 Bq/m³. Canada's 200 Bq/m³ guideline is approximately 5.4 pCi/L.

Radon level / radon concentration

The concentration of radon gas in air, measured in Bq/m³.

Unweighted result / unweighted geometric mean

A result calculated from collected test data without applying the survey's statistical weighting adjustments.

Weighted geometric mean

A geometric average adjusted using statistical weighting so that survey results better represent the distribution of Canadian housing. The 2024 Cross-Canada Survey weighted results by region, community type and building type using 2021 Canada Census data.

If your reading is in pCi/L, the unit US radon information uses, convert it to Bq/m³ with the unit converter.

Canadian and international reference levels

ALARA / ALARP

ALARA means "as low as reasonably achievable." ALARP means "as low as reasonably practicable." These terms describe the principle of reducing radiation exposure as much as reasonably possible while considering practical, technological, social and economic factors.

Canadian Radon Guideline

Canada's national radon guideline is 200 Bq/m³. Health Canada recommends corrective action if the average annual radon level exceeds 200 Bq/m³ in a normal occupancy area.

Corrective action

An action to reduce the indoor radon level to as low as reasonably practicable.

Guideline level / national reference level

A threshold radon level at which corrective action is recommended. Canada's guideline level is 200 Bq/m³. This is also referred to as Canada's national reference level.

WHO reference level

The World Health Organization recommends a national residential radon reference level of 100 Bq/m³. Where this cannot be achieved under country-specific conditions, the reference level should not exceed 300 Bq/m³.

With a result in hand, see what the guideline means for your number.

Radon science

Alpha particle / alpha radiation

Alpha particles are a form of ionizing radiation produced during radioactive decay. Radon measurement devices detect alpha particles produced by radon and its decay products.

Attached fraction

The portion of radon decay products attached to airborne particles such as dust or smoke.

CR-39

A plastic material used in alpha-track radon detectors. The 2024 Cross-Canada Survey identifies CR-39 plastic film as the material used in the alpha-track radon test devices included in the survey.

Free-phase gas movement

The movement of radon-containing soil gases through the ground toward the surface.

Half-life

The time required for half of a radioactive substance to undergo radioactive decay. Radon-222 has a half-life of approximately 3.8 days.

Radioactive decay

The process by which an unstable radioactive atom transforms and releases radiation. Radon is formed through the radioactive decay of uranium and radium.

Radon decay products / radon progeny

The radioactive products formed when radon decays. Some radon decay products can attach to airborne particles such as dust and smoke.

Soil gas

Gas found in the pore spaces of soil. Soil gas can contain radon and can provide a pathway for radon to enter buildings.

Stack effect

Air movement resulting from temperature differences. As warmer air rises and leaves the home, lower levels can become depressurized, allowing air from the ground and outdoors to enter. The effect is generally stronger during the heating season.

Read how radon forms and gets into a house.

Testing terms

Active device / electronic radon monitor (ERM)

An Electronic Radon Monitor (ERM) is an active radon measurement device that continuously measures radon levels at regular intervals and displays or stores the results. ERM is updated Health Canada terminology: ERM replaces the older term digital detector, and professional-grade ERM replaces the older term continuous radon monitor (CRM). Health Canada recommends considering replacement of an ERM five years after purchase unless it has been recalibrated to manufacturer specifications.

Alpha-track detector

A passive radon detector containing a special plastic or film that records damage tracks produced by alpha particles from radon decay.

Breathing zone

The space where residents typically breathe. Health Canada describes the typical breathing zone as 0.3 m to 2.5 m above the floor. For device placement, the detector should be at least 30 cm (1 ft) above the floor.

Electret ion chamber

A passive radon measurement device that uses an electret inside an ionization chamber to measure radiation produced by radon and its decay products.

Heating season

The period during the year when home heating appliances are used to supply heat to a room or space. Health Canada recommends that at least 91 days of a long-term test occur during the heating season.

Lived-in level / lowest lived-in level

The floor or storey of a home with a normal occupancy area. Radon measurements should be made in a normal occupancy area of the lowest lived-in level.

Long-term radon test

A radon measurement that spans a period of at least 91 days.

Measurement uncertainty

All radon measurements include some uncertainty, meaning that repeating a test under the same conditions can produce somewhat different results. Health Canada notes that North American standards from the Canadian Standards Association (CSA) and American National Standards Institute (ANSI) consider it acceptable for repeated radon results to vary by up to ±25%. A result slightly below 200 Bq/m³ may therefore have a true value above the guideline, while a result slightly above 200 Bq/m³ may have an actual radon concentration below the guideline.

Normal living conditions

Residents should not alter their lifestyle during a long-term radon test, because the goal is to measure the home as it is actually lived in.

Normal occupancy area

Any space in which an individual spends more than four hours per day. Spaces that are not used daily but average this level of occupancy over the course of the year, or spaces that may become occupied soon, can also be considered normal occupancy areas.

Passive device

A radon measurement device that does not require an external power source or active sampling to measure indoor radon levels. Passive devices measure cumulative radiation over the duration of the test and provide an average radon level for that period.

Short-term test

A radon measurement lasting less than 91 days (Health Canada). CARST, for real estate screening, separates a screening assessment (at least 4 days and under 7), a short-term measurement (7 to 90 days) and a post-mitigation assessment (at least 48 hours).

See how to run a long-term test in your home.

Mitigation and building terms

Active soil depressurization (ASD)

A radon mitigation system that reduces radon entering a building by drawing soil gas from beneath the building and exhausting it outdoors using a fan.

CAN/CGSB-149.11-2024, Radon control options for new buildings

The Canadian standard addressing radon control options for new buildings. It supersedes the 2019 edition, which was titled Radon control options for new construction in low-rise residential buildings.

CAN/CGSB-149.12-2024, Radon mitigation options for existing buildings

The Canadian standard addressing radon mitigation options for existing buildings.

Gas permeable layer

A layer used beneath a building to facilitate movement of soil gas toward a radon collection system.

Manometer

A pressure-measuring device used with radon mitigation systems to indicate pressure differences within the system.

Mitigation

Action taken to reduce the indoor accumulation of radon.

Passive stack

A passive radon-control system that provides a pathway for soil gas to move from beneath a building and exhaust outdoors without relying on a continuously operating fan.

Radon rough-in

A radon-control system incorporated during construction to provide a pathway and components that facilitate future radon mitigation if required.

Radon rough-in pipe / stub

A pipe incorporated into a new building's radon-control system to provide a connection point for future radon mitigation.

Soil gas barrier

A material or membrane intended to limit the movement of soil gas into a building.

Soil gas collection system

A system installed beneath a building to collect soil gas and provide a pathway for its removal.

Sub-membrane depressurization (SMD)

A mitigation approach that draws soil gas from beneath a membrane installed over exposed soil and exhausts it outdoors.

Sub-slab depressurization (SSD)

A radon mitigation approach that draws soil gas from beneath a concrete slab and exhausts it outside the building.

U-tube manometer

A U-shaped liquid pressure indicator used to show the pressure difference produced by a radon mitigation system.

Read how a mitigation system works.

Certification terms

C-NRPP

The Canadian National Radon Proficiency Program, the national certification body for radon measurement and mitigation professionals, run by the Canadian Association of Radon Scientists and Technologists with Health Canada oversight.

CAL

Certified Analytical Laboratory: the C-NRPP certification for a laboratory that analyses radon detectors, abbreviated CAL.

CARST

The Canadian Association of Radon Scientists and Technologists, the association that runs C-NRPP.

CRMT

Certified Radon Mitigation Professional: the C-NRPP certification for radon mitigation, abbreviated CRMT.

CRT

Certified Radon Measurement Professional: the C-NRPP certification for radon measurement, abbreviated CRT.

Non-interference agreement

A signed agreement, required by the CARST guideline for real estate screening assessments, that the occupants will not interfere with a radon test; it states that anyone who falsifies or assists in falsifying information related to a real estate transaction may be subject to legal action.

Before you hire someone, see what each certification allows a professional to do.