Étude comparative du radon en Suède et au Canada. Baisse au pays nordique et hausse en Amérique du Nord

Comparative study of radon in Sweden and Canada. Decline in the Nordic country and increase in North America.

This is a summary of the international collaborative study between Canada and Sweden on the incidence of radon in buildings in these two countries. We encourage the reader interested in the subject to read the full study.

The study focused on a large cohort of buildings, single family homes, semi-detached homes and townhouses built since 1945. The number of buildings included in Canada is 25,489 and for Sweden 35,596.

The comparative study of our 2 countries has this interesting feature: They are 2 Nordic countries. The curve of smoking, in decrease is similar in the 2 countries. However, the curve of innate presence of radon in the buildings varies in the time with a constant decrease in the buildings for Sweden since the years 1980 whereas it is in constant increase in Canada. For non-smokers the cancer rate is 163% higher in Canada today, a sobering fact. It appeared in the study that the new buildings tested after construction show a lower radon rate which increases in the 2 to 3 years after construction. These buildings were eliminated from the study in order not to induce a bias.

If the buildings in Sweden have a higher radon level before 1970 than in Canada, the buildings of the 1970s and 1980s are comparable (93 - 103 bq/m3). Thereafter the rates increase in Canada and decrease in Sweden. Passing for the buildings of 2010 to 2020 to 28 bq/m3 in Sweden and 131 bq/m3 in Canada is 467% higher. Several parameters have been integrated into a prediction model. Several simulations have also been performed to perfect the understanding of this mountain of data. The predictions suggest a decrease in Sweden to a level _> 15 bq/m3 while for Canada the prediction is an increase _> 175 bq/m3. By 2050 if no drastic changes are made in the way our houses are built.

In Swedish side the decreases of the innate radon occurred in a significant way it occurred everywhere in the country without discernment between the regions. In Canada the increase also occurred across the country with a greater proportion in the prairie region. The period of greatest reduction in Sweden follows the implementation of the air exchanger addition after 1980. In Canada it is considered that it is only since 2010 that this addition is significantly used.

The analysis of building codes shows that Sweden has no specific standards for radon, the application of the building code is prescribed upon publication resulting in immediate changes. In Canada the risk is addressed by the requirement to install basic mitigation infrastructure. Since the building code is subject to provincial and municipal approval, a 5-year implementation gap is generally known. In both countries the downward and upward trends coincide with the adoption of performance-based building codes and a variety of energy efficiency provisions. Based on these observations that the innate risks of radon exposure have taken diametrically opposite trends. It is not suggested that the adoption of this energy performance-based design philosophy is related to these trends.

Energy efficiency concerns have coincided with changes in building ventilation. These concerns have produced more airtight buildings and the addition of mechanical ventilation has been required to ensure a healthy balance of indoor air. While the use of air exchangers in Sweden coincided with a reduction in radon in Canada, the opposite occurred. It became clear during the study that there was no correlation between the use of air exchangers with heat recovery and increased radon in Canada.

Modelling predicts a bleak future in Canada over the next 30 years unless drastic changes are made. Most global strategies are limited and consist of convincing individuals to test and personally invest in post-construction radon mitigation solutions if the administrative rate is deemed too high. The overall effectiveness of this strategy is limited because it relies on many variables, psychological, sociological, economic, and human behavioral to persuade individuals to test for radon, understand the results, and mitigate as needed. A process that is neither inclusive nor fair. A systemic approach to eliminating radon from properties could be that anything built after a certain date be required to have a mitigation system. Costs per installation would be lowered by standardization, more inclusive and fairer.

There is a big difference between the heating modes in the two countries. In Canada, natural gas forced air heating is present in 57% of buildings, 2% are electric. In Sweden in the 2010's district heating represented 70% of the heating and 10% with a natural gas forced air furnace. District heating consists of a central heating plant that produces steam that is distributed through a network of pipes to the buildings. Forced air systems have a major impact on the air and pressure dynamics in a given building. While the use of an air exchanger can reduce the incidence of radon by 25% to 75%, the opposite appears to be true with a natural gas forced air system. The prevalence of this type of heating, particularly on the prairies, where natural gas forced air heating accounts for 77% to 94% of all types of heating. Further study should focus on these more specific aspects, i.e., the heating mode of forced-air systems and also include parameters such as the use of air conditioning in the summer, the presence or not of a chimney, a wood stove, the insulation and age of the building, and the lifestyle habits of the occupants.

Taking into consideration that 70% of the building stock remains to be built over the next 30 years, the future of our children looks grim. The increase of radon in our houses in Canada risks to cause a hecatomb among the non-smokers if no concrete measure is adopted. Therefore the study suggests including in the future National Building Code 2025 the obligation to put in place a complete level 3 mitigation system at the time of construction. Level 1 represents the basic infrastructure with a running duct under the slab connected to a closed duct above the slab. Level 2 consists of a basic infrastructure with the addition of a roof vent without mechanical ventilation. This system relies on the stack effect to reduce the radon level. Level 3 consists of adding a mechanical ventilator to the Level 2 installation.

We recommend that the reader consult the complete study at https://www.nature.com/articles/s41598-021-96928-x

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