Indoor radon regulation using tabulated values of temporal radon variation

Comparative studies on radon seasonal variations in various undeground environments: Cases of abandoned Beshtaugorskiy uranium mine and Kungur Ice Cave

It is well known that one of the most important risk factors in underground environment is the harmful effects of radon. The reasons for strong seasonal fluctuations in radon content in underground environments remain not fully understood. The purpose of this article is to improve existing ideas about this phenomenon. The article presents the results of a study of radon transport in two different underground spaces - the Beshtaugorskiy uranium mine (North Caucasus) and the Kungur Ice Cave (Middle Ural). We have used the direct measurements of the equilibrium equivalent concentration (EEC) of radon progeny in air, as well as the air flow velocity. A very wide range and strong seasonal variations in the radon levels have been recorded in both cases. The EEC has a range of 11-6653 by Bq m-3 and 10-89,020 Bq m-3 in the Kungur cave and the Beshtaugorskiy mine, respectively. It has been established that seasonal fluctuations in radon levels both in the mine and in the cave are caused by the same process - convective air circulation in the underground space due to the temperature difference between the mountain massif and the atmosphere (so called chimney effect). Overall, these results indicate that due to convective air circulation, underground spaces are periodically intensively ventilated with atmospheric air, and then, on the contrary, they are filled with radon-enriched air that seeps into caves or adits from rocks and ores. In both cases, the EEC of radon progeny exceeds the permissible level for the population and workers. The results of this study highlight the need for the development of measures to limit the presence of people in the surveyed underground spaces.

Metrology for Indoor Radon Measurements and Requirements for Different Types of Devices

Indoor radon measurements have been conducted in many countries worldwide for several decades. However, to date, there is a lack of a globally harmonized measurement standard. Furthermore, measurement protocols in the US (short-term tests for 2-7 days) and European Union countries (long-term tests for at least 2 months) differ significantly, and their metrological support is underdeveloped, as clear mathematical algorithms (criteria) and QA/QC procedures considering fundamental ISO/IEC concepts such as "measurement uncertainty" and "conformity assessment" are still absent. In this context, for many years, the authors have been advancing and refining the theory of metrological support for standardizing indoor radon measurements based on a rational criterion for conformity assessment within the ISO/IEC concepts. The rational criterion takes into account the main uncertainties arising from temporal variations in indoor radon and instrumental errors, enabling the utilization of both short- and long-term measurements while ensuring specified reliability in decision making (typically no less than 95%). The paper presents improved mathematical algorithms for determining both temporal and instrumental uncertainties. Additionally, within the framework of the rational criterion, unified metrological requirements are formulated for various methods and devices employed in indoor radon measurements.

A challenging path to rational and harmonised international regulation of indoor radon

The main trends of indoor radon regulation in Europe are expressed through the standard ISO 11665-8. This standard, however, ignores the short-term tests (2-7 days in practice)-the main tests in the USA, and instead requires conducting long-term tests only (2-12 months)-without any justification. Moreover, the temporal (key) uncertainty of indoor radon is ignored altogether, a fact that does not allow the assessment of a room's conformity with a normative at a given reliability (usually 95%). Thus, the current international regulation is neither harmonised nor rational. This paper reports the interim results of storming discussions within the ISO 11665-8 Focus Group, in charge of revising the aforementioned standard. Proposed are the rational criterion for conformity assessment of a room with a normative for both short- and long-term measurements, as well as the indicative values and the algorithm for determining indoor radon temporal uncertainty depending on the measurement duration.

Radon transport in permeable geological environments

This article presents the results of a long-term soil radon and meteorological parameter monitoring study in the fault zone at Mt. Beshtau, North Caucasus, which for more than 3 years. Strong seasonal variations in the radon levels with maxima during summer and minima during winter were recorded. The values of radon exhalation and soil radon concentration have a range of 0.025-25 Bq m ² s ^-1 and 1-170 kBq m ^-3, respectively. In addition, measurements of the air radon concentration, and direction of air movement at the adits mouths of the former uranium mine on the same mountain were carried out. Seasonal radon variations, similar to those observed in fault zones, were recorded at the mouths of adits. It was established that radon anomalies are associated with the periodic release of mine air from the fractures and tunnels into the atmosphere. Above an altitude of 900 m a. s. l., an abnormal release of radon occurs in winter, when the mine air is warmer than the surrounding atmosphere. At the altitudes below 900 m the cold radon rich air blows from the adit mouths in summer. During mine air discharge, radon concentrations in the open atmosphere locally around the adit mouth reach 600,000 Bq m^-3, averaging 50,000-250,000 Bq m^-3. The temporal pattern of radon fluctuations in fault zones and at the adit mouths is similar. A very close correlation between radon levels and atmospheric air temperature was observed both in the fault zone and at the adits mouths. It indicates that radon release in both cases are caused by a single mechanism. This mechanism probably is the atmospheric air circulation in shallow permeable zones due to the temperature difference between the inside mountain and ambient atmosphere.

Short- versus long-term tests of indoor radon for risk assessment by Monte-Carlo method towards effective measurement strategy

There now exists a broad consensus among the European radon community members that long-term measurements are the best practice in managing the risk of indoor radon exposure. This, not with standing the fact that <1% of buildings have been tested in Europe so far. At the same time, US' experience over the years shows more effective regulation has been accomplished through tests that are short-term. This study quantifies the uncertainty of collective risks obtained independently through short- and long-term measurements under the same conditions using the Monte Carlo method that takes into account the number of measurements, as well as the diversity of the spatial distribution of radon concentrations in representative samples of buildings. Simulation results have shown that contrary to the erroneous practice of the European radon community, the accuracy of the assessment of the collective risk due to radon exposure does not in fact depend on the duration of the indoor test at all. The main problem remains ensuring the existance of a representative sample of buildings, especially given limited number of tests. In this regard, recommended is a revision of the regulatory documents of IAEA, ICRP, WHO, and ISO focusing on (i) the principle of the effective measurement strategy based on rational ISO/IEC concepts, (ii) the mass measurements via short-term tests, and (iii) the societal engagement in measurements.

Temporal uncertainty versus coefficient of variation for rational regulation of indoor radon

Significant temporal variations of radon and other air pollutants can be observed in any room, even one with permanently closed windows and doors. Therefore, a question arises: how can one assess the conformity of a room with a normative and make a reliable decision if the test lasts <1 year (days or months)? The measurement protocol fundamentally differs between Europe with its long-term testing tradition lasting several months, and the US where short-term tests of several days are more common. Neither the European nor the American protocols considers the temporal uncertainty of indoor radon, a factor that usually exceeds the instrumental uncertainty (including in long-term tests) and is 2-3 times higher the coefficient of variation (COV) commonly used to estimate temporal variations. This problem significantly complicates the creation of a rational and harmonized ISO standard. At the same time, strict adhering to the fundamental ISO/IEC rules within such concepts as "measurement uncertainty" and "conformity assessment" allows to control the coverage probability or reliability of decision making. Within ISO/IEC, proposed are a criterion of conformity assessment of a room with a normative for both short- and long-term measurements, as well as a statistical algorithm for determining the temporal uncertainty considering mode and measurements duration.

Evaluation of citizen science contributions to radon research

In order to reduce lung cancer due to radon exposure situations, not only authorities and organisations but also citizens may meaningfully contribute to radon mitigation actions. Citizen science (CS) initiatives are recognised for their scientific, societal and policy value related to environmental issues. The purpose of this paper is to identify which CS initiatives in the field of radon exist and evaluate to what extent these CS initiatives contribute to radon research and/or radiation protection from radon. We conducted a systematic review of internet pages and scientific literature (September-December 2020) as well as expert consultation to help us identify and assess CS initiatives on radon (September 2020-February 2021). The ten principles of the European Citizen Science Association have been used as a starting point to develop indicators for the analysis of CS contributions to radon research. The results show that there are at least eight CS initiatives in the world contributing to radon related research which comply, to some degree, with each of the ten principles. In all these initiatives citizens contributed or are contributing meaningfully to radon testing and measurements. However, most of them apply the simplest form of participation (crowdsourcing) and only one focuses on radon mitigation. Moreover, unlike CS initiatives in other environmental areas, those focusing on radon are always led by the authorities and/or universities, in a top-down manner. Yet, results confirm that both the experts in radon-related fields and the citizen scientists from radon prone areas benefit from taking part in radon CS initiatives. Experiences and lessons learned in radon related to CS initiatives are identified and discussed in order to inspire future CS initiatives potentially contributing to reducing exposure to radon as well as to the implementation of national radon action plans.

Seasonal Variation of Radon Concentrations in Russian Residential High-Rise Buildings

Assessment of the annual radon concentration is often required in indoor radon surveys of territories and individual dwellings for comparison with reference levels, studying factors affecting radon accumulation in dwellings, assessment of exposure in epidemiological studies, etc. The indoor radon surveys were carried out in multistorey buildings in eight Russian cities using solid state nuclear track detectors with an exposure period of three months. For these surveys, the estimation of annual indoor radon concentration was required to compare radon levels in buildings of high- and low-energy-efficiency classes located in different cities. To develop approaches to seasonal normalization in high-rise buildings, long-term one-hour radon concentration series obtained applying radon-monitors in 20 flats were analyzed. The dependency of indoor radon concentration on the indoor–outdoor temperature difference was studied taking into account the known natural, technogenic and anthropogenic factors affecting radon levels. The developed model of seasonal variations in multistorey buildings includes winter, summer, and demi-season periods, which differ both in ventilation intensity and dependency of radon concentration on the temperature difference. The developed model allows to estimate annual radon concentration taking into account the actual distribution of outdoor temperatures during the exposure of the track detectors.

VARIATIONS OF INDOOR RADON CONCENTRATION IN TRADITIONAL RUSSIAN RURAL WOODEN HOUSES

Continuous indoor radon measurements were carried out in two traditional Russian rural houses located in different villages of the Moscow region in summer of 2017 and 2018. In additional, in the summer of 2017, continuous measurements of soil gas radon activity concentration at depth 0.8 m and radon exhalation rate from the ground surface near the house were performed simultaneously. It was found that the indoor radon concentration in rural houses is subject to strong daily variations, which are characterized by highs at night and lows during the day. Indoor radon concentration is directly proportional to indoor and outdoor temperature difference and inversely proportional to wind speed. While the radon exhalation rate from the ground surface, as well as the ventilation of premises (opening doors and windows) practically do not affect the concentration of radon in Russian rural wooden houses.

Involving schoolchildren in radon surveys by means of the "RadonTest" online system

A 'citizen science' approach was evaluated as an approach to organize an extensive radon survey to be representative of the population of either single regions or a whole country. The "RadonTest" online system allowed schoolchildren to undertake and record short-term radon tests in their homes. Measurements were carried out in Israel using charcoal in miniature flacons and simple detectors with high sensitivity. Among other things, the "RadonTest" online system implements an alternative principle of building a radon map, allowing the display of radon tests more clearly than the traditional approach, while ensuring the confidentiality of test participants. Examples of public radon maps are presented, and the first test results are discussed. A scientifically based approach for the effective identification of buildings with a high radon concentration, based on the principle of radon regulation, is proposed.

Modelling of the temporal indoor radon variation in Bulgaria

In this study, temporal variations of indoor radon concentrations in Bulgaria were investigated. The radon concentrations were measured by nuclear track detectors as part of the Bulgarian National Survey, performed in the dwellings of 28 regional districts. The detectors were exposed through a year in two consecutive time periods of different lengths. For 2433 dwellings, measurements could be completed for both time periods, while for 345 dwellings they could only be completed for one of the periods. To estimate any missing radon concentrations, a temporal correction procedure was developed. This procedure, which included development of a linear correlation between the ln-transformed radon concentrations from the 9-month period [CRn(L)] and from the 3-month period [CRn(S)]. A normal distribution of the data, which is a condition for linear regression, was achieved when the ln-transformed radon concentrations were grouped by climate zone, then by regional districts, and finally by the presence/absence of a basement in the investigated building. The linear models obtained for each group showed reasonable coefficients of determination (R² ≈ 0.50) and root mean square errors (RMSEs) of about 0.50. When these correlations were used to reconstruct radon concentrations in missing measurement periods, it turned out that the reconstructed data (for 345 dwellings) were within the 95% confidence interval of the measured data (for 2433 dwellings). The geometric means of CRn(L) and CRn(S) were 76 Bq/m³ and 100 Bq/m³, respectively, for 2433 dwellings, which are almost equal to those of 75 Bq/m³ and 98 Bq/m³, which represent the measured and reconstructed data together (for 2778 dwellings).