Guide for radon measurements in homes

About

This guide provides technical guidance for individuals and organizations carrying out long-term radon testing in low-rise residential buildings and individual units in multi-unit residential buildings (MURBs) (collectively referred to as homes in this guide). It provides information on how to measure radon levels in homes, for the purpose of comparing against the Canadian Radon Guideline level to make informed decisions about managing exposure and mitigation. Measurements taken following this guide will provide a reasonable estimate of a home's average annual radon level and assist with determining if mitigation is necessary.

The scope of this guide is limited to:

selection of radon measurement devices,
device placement,
measurement duration,
reporting, and
interpretation of measurements.

The Guide for Radon Measurements in Public Buildings is available for individuals looking to test radon in public buildings, such as workplaces, schools, daycares, hospitals, care facilities, and several units or building-wide measurements in MURBs.

More information:

Radon: Long-term test instructions (for homeowners)
Radon Resources

Radon

Radon is a naturally occurring radioactive gas formed by the radioactive decay of uranium in the natural environment. It is invisible and odourless, but radon measurement devices can easily detect it. When radon is released from the ground into the outdoor air, it is diluted and not a concern. In enclosed spaces, like homes, radon gas can accumulate to high levels and become a health risk.

The International Agency for Research on Cancer (IARC) has identified radon as a group 1 carcinogen. It is the number one cause of lung cancer for non-smokers in Canada. An individual's risk of lung cancer from radon depends on the concentration and duration of an individual's exposure. As such, individuals with long-term exposure to high radon levels are at greater risk of developing lung cancer.

Soil gas is the largest source of indoor radon. Radon can enter a home anywhere the building is in contact with the ground. Typical entry points include cracks in foundation walls and floor slabs, construction joints, gaps around service pipes, support posts, floor drains, or sumps (Figure 1). Radon will also move through the foundation. While higher radon levels are typical in basements and crawl spaces, elevated radon levels can be found throughout a home. Radon outgassing from water may be a potential source when a home's water supply is from a private well. Typically radon from water does not affect indoor radon levels as much as soil gas.

Figure 1. This diagram illustrates radon movements inside and outside a building. — **Figure 1. This diagram illustrates radon movements inside and outside a building**

Radon gas is in all buildings in contact with the ground. Testing is the only way to know the radon level in a specific home and to determine if mitigation is necessary. Health Canada recommends every home should be tested, no matter where it is located, the type of building, or if it already has a mitigation system. Radon can vary widely between homes, even in homes in the same building, or buildings on the same street.

Canadian radon guideline

The Canadian Radon Guideline (the guideline) was established to help Canadians manage their risk of radon induced lung cancer. Health Canada collaborated with the Federal Provincial Territorial Radiation Protection Committee to review the health risk to Canadians from exposure to radon, using both a risk assessment and feedback obtained from a public consultation.

The guideline is as follows:

take corrective action if the average annual radon level exceeds 200 Bq/m³; in the normal occupancy area,
the higher the radon level, the sooner corrective action should be taken,
the corrective action should reduce the radon concentration as much as is practicable, and
the construction of new buildings uses techniques that minimize radon entry and will help remove radon after construction is completed, if necessary.

NOTE: 37 Bq/m³ is equal to 1 pCi/L

What to test with

There are many measurement devices available to test a home for radon. These devices work by measuring the alpha particles from the decay of radon and its decay products. There are many different detector technologies used in these devices, and they can generally be classified as either passive or active devices; both are available in Canada. The types of devices described below are currently recommended by Health Canada as acceptable for use with the measurement strategies described in this guide, provided they are C-NRPP approved devices.

Health Canada recommends the use of long-term radon devices that have passed the Canadian National Radon Proficiency Program (C-NRPP) performance testing. C-NRPP provides a list of approved passive devices and professional-grade electronic radon monitors (ERMs). C-NRPP also conducts performance testing for ERMs and has developed a list of approved electronic monitors. Both passive and active devices can provide accurate measurements when conducted according to this guide. Health Canada does not recommend the use of any specific device over another on these lists.

Passive radon devices

Passive radon measurement devices do not require an external power source or active sampling to measure indoor radon levels. These devices rely on the natural diffusion of radon into a detection chamber and measure the cumulative radiation from radon over the duration of the test. The collected signal from the radiation is read after the test is complete. Passive devices can only provide an average value of the indoor radon level over the test period.

The start and end dates must be recorded to at least the nearest day. These devices do not record time so the start and end dates of the test must be manually recorded to know the test period of the measurement. Passive devices are easy for anyone to deploy, but require trained individuals to read the output and produce a report that reflects the average radon level over the course of the measurement.

Health Canada recommends two types of passive devices, alpha track detectors and electret ion chambers.

Alpha track detector

Alpha track detectors (ATD) are the most common devices in Canada. These devices contain a special plastic or film inside a filter-covered detection chamber. The chamber allows the entry of radon, while filtering out the entry of its decay products. Alpha particles released in the chamber damage the plastic or film inside the device leaving damage tracks. The number of tracks correlates with the integrated radon level over the test period.

At the end of the test period, ATDs must be sent to a laboratory where the tracks are counted and analyzed to determine the radon level. The device should be sent according to the manufacture or lab instructions provided with the unit.

Individuals should ensure that their test is completed before the manufacturer-specified expiry date to ensure accurate results. This expiry date is clearly labeled on the packaging or the device itself.

Health Canada recommends using long-term ATDs. Short-term ATDs are available but short-term measurements are not appropriate for informing mitigation decisions.

Electret ion chamber

Electret ion chambers contain a positively charged disk (electret), in an electrically conductive plastic canister (chamber). During the measurement period, radon diffuses into the detection chamber with the exposed electret. Radiation emitted by radon and its decay products ionizes the air molecules inside the chamber and the negatively charged ions impart a charge onto the positive electret, reducing the electret voltage. The drop in voltage on the electret over a known time interval is measured and analyzed using specific calibrated readers to determine the average radon level. This is usually done through a qualified laboratory. The detectors are not destroyed during measurement or analysis, so these devices can be reused and readings can be taken at intervals during the measurement period. The electret will need to be replaced once its voltage is below the usable level. Refer to manufacturer's instructions to determine when to replace an electret.

Different types of detection chambers and electrets are available and should be used based on the measurement requirements. Refer to the manufacturer's user manual to select the appropriate chamber and electret based on measurement requirements. Health Canada recommends using long-term electrets. Short-term electrets are available but short term measurements are not appropriate for informing mitigation decisions.

Active radon devices

Active radon measurement devices are electronic devices that continuously measure radon levels and provide real-time or near real-time readings. These devices collect air samples either through a small pump or natural diffusion into a detection chamber. Within the chamber, various technologies (alpha scintillators, ionization chambers, or solid-state detectors) detect alpha particles emitted by radon and its decay products. They have on-board electronics to measure, analyze, and provide radon level readings concurrent to the test. They can collect independent or integrated measurements, and provide discrete or averaged readings for specified time intervals.

The only active measurement devices recommended by Health Canada for long-term measurements are ERMs. These devices vary greatly in terms of functionality, features, and usability; individuals should be familiar with the capabilities and shortcomings of any ERM prior to use.

Electronic radon monitors

ERMs continuously measure radon levels at regular time intervals and provide results either directly on a digital screen or through a smartphone application. Some ERMs can store the readings for later evaluation or reporting, or include other indicators of air quality such as temperature, humidity, and pressure.

Health Canada recommends that users consider replacing these devices five years after their purchase date to ensure that measurements remain accurate, unless they are recalibrated to manufacturer specifications.

NOTE: Many ERMs targeted at the public cannot be recalibrated after purchase.

Health Canada recommends selecting ERMs that have passed the C-NRPP performance testing for conducting long-term radon measurements in homes. As well, Health Canada independently studies the performance of new ERM models as they enter the market. Based on the assessments made by C-NRPP and Health Canada, devices that do not meet performance requirements are recalled and listed on Government of Canada's Recalls and Safety Alerts

A subset of ERMs target professional applications. These professional-grade ERMs are typically more durable, sensitive, accurate, have a wider detection range, and have additional features or software relevant to professional applications. Professional-grade ERMs should be recalibrated by the manufacturer or a C-NRPP/NRPP accredited facility when required, to ensure reliable results. C-NRPP has a separate approval process for professional-grade ERMs and has a list of approved professional devices.

NOTE: Electronic Radon Monitors (ERMs) and professional-grade ERMs are updated terminology. ERM replaces the term Digital Detectors from previous versions of this guide and encompasses all current active radon measurement devices. Professional-grade ERM replaces the term Continuous Radon Monitor (CRM) from previous versions of this guide to emphasize their professional-grade quality and application.

This update reflects the advance of radon measurement technology, which has led to features that were once only in professional-grade ERMs (for example the capacity to provide hourly measurements or to record air quality parameters) now being found in more ERMs targeted at the public. Health Canada recommends using these updated terms when referring to active radon measurement devices to maintain clarity and consistency in communications and documents.

C-NRPP uses the terms Consumer-grade ERM, and Professional-grade ERM to split ERMs into two distinct categories, one designed for use by consumers and the other by professionals.

How to test

It is important to consider the appropriate placement of radon measurement devices and timing, for measuring radon in homes. The goal of testing is to determine the average annual radon level in normally occupied areas of the home, for the purposes of making mitigation decisions. The criteria outlined below achieves this goal, either through direct measurement of the average annual radon level or an estimate based on a measurement of no less than 91 days using conservative assumptions.

When to test

Radon testing should take place over a period of no less than 91 days. Radon levels in homes vary over time due to factors such as residents' habits, building ventilation systems and construction, entry pathways, prevailing weather conditions, daily and seasonal fluctuations, and more. To accurately determine the average annual radon level in a home, Health Canada recommends conducting radon tests over a period of 3 to 12 months. Longer tests give a more accurate estimate, smoothing out variations caused by these factors.

The test should be conducted during the heating season, so that 91 days of the test is during the heating season. In Canada, this is typically from October to April, but can vary by location. Testing during the heating season is preferable as it provides a conservative annual estimate, as indoor radon levels are typically higher during colder months. This is primarily due to less radon escaping the home, as residents keep windows and doors shut, and more radon entering the home from the soil due to the stack effect. Tests that occur outside of the heating season may underestimate the average annual radon level.

NOTE: Residents should not alter their lifestyle during a long-term radon test.

What room to test

All measurements should be made in a normal occupancy area of the lowest lived-in level of the home. A normal occupancy area is any area occupied by an individual more than 4 hours per day. Spaces that are not used everyday, but on average, over the course of the year, are used for this same amount of time may also be defined as a normally occupied space. Areas that may become occupied soon can be considered a normal occupancy area, for example, renovating a basement to add a bedroom, or changing how a space is used to add an office.

NOTE: Example of a space that is not used everyday but may be considered a normal occupancy area: Anne works part time as an artist, and spends a significant amount of time (12hrs a day) in her basement studio on most weekends. She also spends a few hours during the week in her basement. Even though she is not spending 4 hours each day in the basement, the average time spent in the basement over a year is greater than 4 hours per day and the basement would be considered a normal occupancy area.

Ideal measurement locations include:

family rooms,
living rooms,
dens,
playrooms,
offices, and
bedrooms.

Bedrooms on the main floor or basement should be prioritized; residents generally spend more time in their bedrooms than in any other room in the house. If children are in the home, areas such as basement-level playrooms should be tested.

NOTE: The basement is only considered a potential measurement location if it includes a normal occupancy area.

Tests should not be conducted in the:

kitchen,
laundry room, or
bathrooms.

These locations are not appropriate to conduct radon tests, as they typically have different air quality and ventilation characteristics compared to the rest of the home. In homes with open floor plans, individuals should choose a location in the living area of the open space and avoid the previously mentioned areas.

Figure 2. Potential rooms for radon testing locations in a home. Locations that are appropriate (✓) for radon testing, such as a bedroom, living, or office, and locations that are not appropriate (✘) for radon testing, such as a kitchen, bathroom, or storage room, are indicated.

Where to place a device

When choosing a place for the device within a room, considerations should be made to ensure that the device is not disturbed or lost. Select a place that is out of the reach of children or pets. Place the device in the approximate breathing zone, with access to the main air space, following the placement criteria below.

NOTE: Examples of appropriate places for a measurement device include a shelf, end table, dresser, or suspended from the ceiling.

ERMs may have limited placement options due to being connected to a wall socket or a power cable. In these situations, users should follow the placement criteria to the extent that is reasonably possible and any specific placement instructions from the manufacturer. Always install new batteries for battery operated ERMs before starting a test to prevent any loss of power during the measurement period.

**Figure 3. Potential detector placement in a room. Locations that are appropriate (✓) for radon testing and locations that are not appropriate (✘) for radon testing are indicated.**

Placement criteria

For more specific recommendations relating to the placement of measurement devices, refer to Appendix II - placement specifics.

Do:

Place the device where it will not be disturbed.
Allow space for air flow around the device.
Place the device in an area occupied for four or more hours per day.
Place the device on the lowest lived-in level of the home.
Wipe the surface with a dry cloth before placing the device.

Do not:

Place the device in contact with the floor, ceiling, or exterior wall.
Place the device in enclosed spaces such as a closet or drawer.
Place in areas with high humidity such as in sunrooms, near humidifiers, or in bathrooms.
Place the device near heat sources or in direct sunlight such as near a fireplace, on a windowsill, or over a radiator.
Place the device near air currents caused by heating, ventilation, and air conditioning systems such as on a vent, near a door, or near windows.
Place the device next to or on electrically powered devices or network appliances such as computers, Wi-Fi routers, television sets, stereos, or speakers; as some measurement devices may be affected.
Place the device near typical radon entry points that may artificially increase measured levels, and are not representative of the typical breathing zone such as near sump holes, in crawl spaces, or next to exposed cracks in the foundation.

Other considerations

Damaged devices: If the device is dropped, broken, or potentially compromised in some way, individuals should contact the manufacturer for further information and guidance. Alternatively, users can choose to repeat the test with a new device.

High readings from ERMs: If an ERM measures a radon level greater than 3700 Bq/m³, consult the manufacturer or a C-NRPP certified radon measurement professional. This is the upper limit for some ERMs, and the reading should be verified.

Floors above ground level: Homes where the lowest lived-in level is not in contact with the ground should still be tested. Although these homes typically have lower radon levels, they can still have a level above the guideline.

Homes with mitigation systems: Homes with mitigation systems should still be tested when there are no prior measurements available. Although these homes typically have lower radon levels, these homes can still have a level above the guideline, and may require further corrective action. The only way to determine the efficacy of a mitigation system is by testing the home.

Loss of power: If an ERM loses power during a measurement, individuals should check the integrity of the measurement data. If the data is still intact, then the measurement can continue once power to the device is restored. If not, it may be necessary to start the testing period over again. Most battery operated ERMs do not preserve data in the case of loss of power. It is important to use new batteries when starting a test with a battery-operated ERM. ERMs that require removable, external, or cloud storage should be set up according to manufacturers' instructions.

Using a single device to test multiple locations: ERMs and electrets can be used to test multiple locations. Before testing a new location with an ERM, reset the device prior to a new test in a new location.

Quality assurance / quality control: Professionals conducting radon measurements and laboratories analyzing radon measurement devices should comply with C-NRPP's Quality Control and Quality Assurance Manual for Radon Sampling and Analysis conducted by Radon Measurement Professionals and Laboratories.

Reporting and interpretation of results

Report criteria

After a completed test, a report should be provided detailing the results of the test, and all residents of the home should be informed. Depending on the device and company used, these reports may be created in a number of different ways. The report must be clear, easy to understand, and provided in a digital or physical format as requested by the individual.

NOTE: Reports are provided if an individual tests their home with a passive radon detector or a hired radon professional. For individuals that test with an ERM themselves, depending on the ERM device, it may not be possible to generate a detailed report for their test.

Basic report content

The report should have the following information:

Date the report was issued.
Complete physical address of the home where the measurement was taken.
Start and end date of the measurement.
Results of the measurement reported in Bq/m³ for the measurement period:
1. with the uncertainty of the measurement in Bq/m³; or,
2. if the result is less than the limit of detection or quantification, the limit should be reported instead with a statement the result is below that specific limit.
A comparison of the measurement result to the guideline level and the recommended action as per the guideline.
If it can be determined that any of the conditions in Table 1 occurred during the measurement period then the appropriate disclaimer should be included.

Table 1: Testing conditions that may impact the validity of the measurement
Condition	Example disclaimer
The test period is less than 91 days.	This test was less than 91 days; Health Canada recommends that measurements occur over a time period no less than 91 days. Shorter test periods may not be sufficient to estimate an annual average. A new test is recommended.
The radon measurement device was tampered with or damaged.	The radon measurement device was compromised prior to analysis. The results of this test may not be representative of the location. A new test is recommended.
Less than 91 days occurred during the heating season.	Not enough of the test occurred during the heating season. Health Canada recommends that tests occur during the heating season. This measurement is still representative of the radon level over the test period that occurred. However, testing periods that occur in part or wholly outside the heating season may not provide a sufficiently conservative estimate of an average annual radon level.
Location and placement of the radon measurement device deviated from the guidance.	The placement of the radon measurement device deviated from Health Canada's placement guidance. This measurement is still valid for the location that was tested. However, devices placed in non-standard locations may not provide a sufficient estimate of an average annual radon level.

Supplementary report content

A report should have the following information if appropriate:

Name and contact information of all certified professionals or companies that conducted the measurement or analysis.
Room and floor where the device was placed in the home.
Serial number or identification number of the device used for the measurement.
Type, manufacturer, and model of the device used for the measurement.
Information on the validity of the device (for example, expiry date of the ATD, calibration date of professional grade ERM).
Photos of the device serial number, and of the device in the test location.
Statement of the Health Canada radon guideline.

Interpretation of results

A measurement following this guide provides a conservative estimate of an individual's average annual radon level in their home. Only the long-term average value should be used for this estimation. Passive radon measurement devices are capable of providing only this value. Active radon measurement devices, such as ERMs, are often capable of displaying various measurement periods and statistics. Short-term or non-average values are not to be used as a substitute for long-term average values when determining corrective action. Some ERMs do not report long-term averages; the long-term average radon level can be calculated using the calculations in Appendix III - Sample calculations.

The goal of measuring indoor radon is to determine if corrective action should be taken to mitigate the adverse health risks from radon inhalation. While the health risk from radon exposure below the Canadian Guideline is small, there is no level that is considered risk free. It is the choice of each individual to decide what level of radon exposure they are willing to accept. Regardless of radon level, any action taken that reduces an individual's radon exposure corresponds to a decrease in their health risk.

If a measurement is above the Canadian Radon Guideline level, the building owner should take steps to reduce the exposure of all residents. Health Canada recommends:

individuals mitigate within 1 year for radon levels higher than 200 Bq/m³.
individuals take action sooner if the radon level is higher.
Mitigation measures should reduce the radon level in the home to as low as reasonably achievable (ALARA).

Individuals can find more information on corrective actions and mitigation solutions in the Radon - Reduction Guide for Canadians or by contacting a C-NRPP certified Radon Mitigation Professional.

Re-testing

Follow-up radon testing may be necessary in some cases. Health Canada recommends individuals re-test their home the next heating season in the following situations:

After any renovation that affects the structure or ventilation of the home (for example renovating the basement, installing a new furnace, adding a bathroom).
After energy retrofits to the home to make it more energy efficient (for example installation of new windows, insulation, sealing).
After any excavation or earthwork near the foundation of the home (for example replacing a septic tank, exterior waterproofing, terracing, installing drainage systems).
If the basement or main floor was not tested and has since become the lowest lived-in level of the home.
After any radon mitigation system is installed, to ensure performance of the system.
In a newly built home, 2 years after year of construction; note that the home should still be tested the first heating season after occupancy.

Additionally, if an active soil depressurization system is installed, the home should be tested every 5 years to ensure the system is continuing to function as intended.

Appendix I - Frequently asked questions

Question: What should I do if my test has lasted longer than 12 months?

Answer: You should contact the manufacturer or laboratory to determine if the measurement is still valid.

Question: I live above the second floor in an apartment building, should I test?

Answer: Homes above ground level should still be tested. Although, these homes typically have lower radon levels, there is still a risk that it could exceed the guideline level.

Question: I moved into a home that has a mitigation system installed. Do I still need to test?

Answer: Health Canada recommends that everyone test their home. If you don't know the radon level in your home, you should test. Additionally, Health Canada recommends that homes with active mitigation systems should be retested every 5 years to ensure the system is functioning as intended.

Appendix II - Placement specifics

The requirements below represent best practice for device placement. In the event that it is not feasible or reasonable to fully implement these specifications, Health Canada recommends following them to the extent possible. Radon measurement device placement should be:

in a room on the lowest level of the home with a normal occupancy area such as a bedroom, office, playroom, living room in a basement or main floor.
in a place where the device will not be moved during the measurement period.
in the typical breathing zone (at least 30 cm, or 1 ft, above the floor).
at least 30 cm from walls or ceilings.
in a place which falls within the manufacturer's recommended range for temperature, humidity, and pressure. Typical ranges for these parameters are as follows:
- Temperature: 0 to 35°C (32 to 95 °F)
- Relative humidity: below 80%
- Pressure: 70 to 110 kPa (10 to 16 PSI)
at least 1 m away from vents, windows, doors, or anything that may interfere with normal airflow.
away from electronic or network devices, which may affect measurements.
away from objects to allow normal airflow around the device, except the surface the device is placed on or mounted to. Health Canada suggests a minimum of 10 cm (4 in) between the device and other objects.

Appendix III - Sample calculations

This appendix provides detailed methods for calculating the arithmetic average radon concentration over a given time period. These calculations are applicable for situations where ERMs do not provide a long-term average and only shorter-term measurement data are available (for example, average hourly measurements instead of a long-term average value). Average radon concentrations calculated using the methodology below can be directly compared to the guideline value of 200 Bq/m³ for decision-making purposes, provided they meet the other testing requirements in this guide.

Individuals are reminded that Health Canada does not recommend testing for periods shorter than 91 days. The 8 hour period used in the sample calculations is for demonstrative purposes only and should not be interpreted as an appropriate test duration.

For equal time intervals

To calculate the average radon concentration for this period, a simple average (Equation 1) can be used to calculate the long term average from smaller interval measurements.

Equation 1: Calculation for the average long-term radon concentration when the measurement intervals are all equal. This is calculated by dividing the sum of all interval radon measurements by the number of intervals. Where Rn_i is the radon measurement for the interval, n is the number of intervals, and Rn' is the long-term average radon concentration.

A sample dataset is provided for this calculation below.

Table 2: Sample data showing radon measurements taken every hour over 8 hours
Date	Time	Interval duration (hours)	Radon (Bq/m³)
June 10^th, 2024	11:00 am - 12:00 p.m.	1	144
June 10^th, 2024	12:00 p.m. - 1:00 p.m.	1	159
June 10^th, 2024	1:00 p.m. - 2:00 p.m.	1	159
June 10^th, 2024	2:00 p.m. - 3:00 p.m.	1	177
June 10^th, 2024	3:00 p.m. - 4:00 p.m.	1	157
June 10^th, 2024	4:00 p.m. - 5:00 p.m.	1	190
June 10^th, 2024	5:00 p.m. - 6:00 p.m.	1	182
June 10^th, 2024	6:00 p.m. - 7:00 p.m.	1	215

To calculate the average radon concentration for this period, sum the individual hourly measurements and then divide by the number of intervals during the test.

**Figure 4. Example calculation when measurement intervals are equal**

For irregular time intervals

For irregular time intervals, measured levels of radon need to be corrected based on the length of time that they represent. This can be done using weighting factors. The weighting factor is the length of the measured time interval divided by a reference time interval. The units for the measurement and reference intervals must be the same, and consistent (for example both values are in minutes). Once the weighting factors have been determined, they can then be used to estimate the average radon concentration for the measurement period using the equation shown below:

Equation 2: Calculation for the average long-term radon concentration when the measurement intervals are not equal. This is calculated by dividing the sum of all products of each interval radon measurement by the respective interval weight, calculated using Equation 3, by the sum of all the interval weights. Where w_i is the weight factor for the interval measurement, Rn_i is the radon measurement for the interval, and Rn' is the long-term average radon concentration.

Equation 3: Calculation of weight factor for the interval measurement. This is the interval duration divided by the reference interval. This weight factor is calculated for each interval. Where i_M is the interval duration, i_R is the reference interval, and w_i is the weight factor for the interval.

A sample dataset is provided for this calculations below.

Table 3: Sample data showing measurements are irregular intervals over the course of 8 hours
Date	Time	Interval Duration (minutes)	Radon (Bq/m³)	Weighting factor
June 10^th, 2024	11:00 am - 11:45 a.m.	45	200	0.75
June 10^th, 2024	11:45 a.m. - 12:15 p.m.	30	207	0.5
June 10^th, 2024	12:15 p.m. - 1:30 p.m.	75	222	1.25
June 10^th, 2024	1:30 p.m. - 2:30 p.m.	60	185	1.0
June 10^th, 2024	2:30 p.m. - 3:45 p.m.	75	170	1.25
June 10^th, 2024	3:45 p.m. - 5:45 p.m.	120	230	2.0
June 10^th, 2024	5:45 p.m. - 6:00 p.m.	15	215	0.25
June 10^th, 2024	6:00 p.m. - 7:00 p.m.	60	195	1.0

The calculation of average radon concentration with measurements taken at irregular time intervals for a period of 8 hours.

In this case, the reference interval will be 60 minutes. The example below shows the calculation of the first weighting factor.

**Figure 5. Example calculation of the weighting factor for an interval**

**Figure 6. Example calculation when measurement intervals are not equal**

Defined terms

Active soil depressurization system: A radon mitigation system that reduces the radon level in a home. The system removes the air pressure difference between the house and soil, and exhausts the soil gas outside using a fan.
Average annual radon level: The average radon level in a home, calculated over a twelve-month period.
As low as reasonably practicable/ As low as reasonably achievable (ALARP/ALARA): The principle that radiation exposure should be as low as possible using reasonable effort and weighing the social, economic, and technological costs and limitations with the health benefits. While the guideline level for mitigation is 200 Bq/m³, it is expected that mitigation measures will reduce radon to levels that are ALARA. The Guideline level of 200 Bq/m³ is not a recommended stopping point for mitigation if it is reasonable to go lower, with social, economic, technological, and other factors considered.
Becquerel (Bq): International System unit for radioactivity. One becquerel corresponds to one nuclear decay per second. For radon gas, one becquerel is one nuclear decay of radon, emitting one alpha particle (a form of ionizing radiation) per second.
Becquerel per cubic metre (Bq/m³): International System unit for the concentration radioactive decay in air.
Breathing zone: The summation of all space where residents typically breathe (i.e., the region around their face and immediately adjacent). The zone will depend on the use of the room (for example: bedroom vs. living room) and the physical characteristics of the individuals using the room (for example: children vs. adults). Typically this zone is considered from 0.3m to 2.5 m from the floor of the room.
Corrective action / Mitigation action: An action to reduce the indoor radon level to as low as reasonably practicable.
Group 1 carcinogen: A substance that causes cancer; there is sufficient evidence of the substance causing cancer in humans. This is a classification by the International Agency for Research on Cancer used to evaluate the strength of evidence for cancer-causing substances.
Guideline level: A threshold radon level at which corrective action is recommended. Determined by the Canadian Radon Guideline to be 200 Bq/m³. This is also referred to as Canada's national reference level.
Heating season: A period of time during the year when home heating appliances are used to supply heat to a room or space directly. This time period can span different durations depending on the region and climate patterns, but generally coincides with the colder months of the year.
High radon level: A radon level that exceeds the guideline reference level of 200 Bq/m³.
Home: A low-rise residential building or a single unit in a multi-unit residential building.
Home heating appliance: Any appliance that is used to heat a home. This includes all fixed, and non-fixed appliances that are used to heat a home, or a space within the home.
Lived-in level: The floor or story of a home with a normal occupancy area.
Long-term radon test: A radon measurement that spans a time period of at least 91 days.
Low-rise residential building: Building intended for private occupancy with up to and including four stories in height.
Mitigation: Action to reduce the indoor accumulation of large amounts of radon.
Multi-unit residential building (MURB): Residential building that contains two or more units intended for private occupancy.
Normal occupancy area: Any area occupied by an individual for more than 4 hours per day. Spaces that are not used everyday, but on average, over the course of the year, are used for this same amount of time may also be defined as normally occupied.
Outgassing: The release of a dissolved, frozen, or trapped gas from solid or liquid material.
Radon level: The concentration of radon gas in air, measured in Bq/m³.
Residential building: A building intended for private occupancy.
Short-term: Time period that is less than 91 days.
Soil gas: Gas found in pore spaces of the soil.
Stack effect: Air movement resulting from temperature differences. As warmer air rises due to its lower density, which is forced out of the home, the lower levels of the home become depressurized. This allows cooler air from the ground and outdoors to enter the lower floors of a home. This effect is strongest during the heating season.

List of acronyms

ATD: Alpha-track detector
ALARA: As low as reasonably achievable
ALARP: As low as reasonably practicable
CARST: Canadian association of radon scientists and technologists
C-NRPP: Canadian national radon proficiency program
CRM: Continuous radon monitor
ERM: Electronic radon monitors
MURB: Multi-unit residential buildings

Acknowledgements

Health Canada would like to acknowledge the Canadian Association of Radon Scientists and Technologists (CARST) for the support and collaboration they provided during the development of this guide. The invaluable studies conducted by CARST support the guidance by Health Canada. Health Canada would like to dedicate this guide to Adelene Gaw. Adelene was an exceptional member of the radon and radiation protection community, and was instrumental to the development of this version of the radon testing guide.

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Date modified:: 2024-11-29

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