Radon Entry Rate Research Articles

Radon indoors source potential from soil gas in a temperate climate: impact of infiltration rate and seismicity

Indoor radon source potential from unground soil was monitored using prototype devices approaching a dwelling with a cellar basement at 1 depth from the soil-atmosphere interface. Therefore, the radon concentrations in soil gas were monitored at 1 m depth. Integrated radon measurements were performed, and the results correlated with meteorological parameters. The influence of the difference in outdoor and device-soil temperature was considered, and the infiltration rate was calculated. The effect of the soil temperature gradient on the soil radon entry rate was evaluated. The indoor radon entry rate due to the soil gas was 7.0 ± 2.7 Bq m−3 h−1. The radon entry rate was 5.0 ± 0.8 Bq m−3 h−1 due to diffusion. In contrast, the advection-drive flow of soil gas is ranged up to ± 4.0 Bq m−3 h−1. So, the infiltration rate of the model dwelling was 0.7 (± 0.5) × 10−1 h−1 if only the stack effect occurred. The radon levels in tap water were measured, and the radon entry rate was estimated at 1.3 ± 0.7 Bq m−3 h−1. If the ventilation rate is low or seismic faulting appears, the soil radon entry is increased by one order of magnitude. The soil radon appeared like the building materials, having 1/3 of the total indoor radon entry, while outdoor air was slightly lower (28%), with tap water at 5%. The resident’s mortality risk occurred at < 2.5% for typical dwellings in temperate climate areas founded on sand-gravel underground. The risk rises to 34% with an extremely low ventilation rate between indoors and outdoors or high radon entry from the soil due to seismic faulting.

Relationship between Ra-226 activity concentration in building materials and indoor radon concentration: An example of Russian high-rise residential buildings

The worldwide trend toward the construction of high-rise buildings with high energy efficiency highlights the role of building materials as a source of indoor radon in the modern urban environment. The aim of the study is to analyze the relationship between the Ra-226 activity concentration in building materials and indoor radon concentration using the example of multi-story buildings in Ekaterinburg. Measurements of the activity concentration of natural radionuclides in building materials were carried out using a new non-destructive method. A radon survey conducted early provided the data on indoor radon concentrations in the same apartments. The obtained Ra-226 activity concentrations in building materials in high-rise buildings were found to be relatively low, ranging from 9.1 to 51 Bq/kg. The typical radon entry rate by diffusion from building materials for modern Russian multi-story buildings can be accepted as equal to 0.5 Bq/(m3∙h) per 1 Bq/kg of Ra-226 activity concentration. Ra-226 in building materials has been shown to be a primary source of indoor radon in modern high-rise buildings, where this factor can cause indoor radon concentrations above the reference level of 100 Bq/m3 at low air exchange rates. The activity concentration of Ra-226 in building materials should be considered a separate parameter for regulation within the national radiation protection systems.

Annual monitoring of soil radon behavior and entry into building

A simple experimental scheme is proposed to study the concentration behavior and mechanism of soil radon transport from beneath a building foundation. In addition to the results of the annual monitoring of soil radon concentration and environmental factors, the calculated results of the annual continuous monitoring of the soil radon entry rate into experimental room with high levels of indoor radon are presented. This room is located in the basement of one of the buildings in Haifa, Israel. The correlation between radon behavior and environmental factors is discussed. It is found that the soil radon concentration beneath the building is maximum in the winter season due to very heavy rains. There is an absence of soil radon entry by only convection mechanism into the experimental room for the summer and autumn seasons; however, the indoor radon concentration remains high (about 500 Bq m-3) due to diffusion of soil radon. A regular soil radon entry into the experimental room by convection is observed in the winter and spring seasons with a maximum, approximately at the beginning of the spring season, and therefore, the indoor radon concentration is twice as high as in the summer and autumn seasons. The obtained results indicate that not only convective process but also diffusion of soil radon plays a significant role in the formation of indoor radon.

Non-destructive measurements of natural radionuclides in building materials for radon entry rate assessment

To control the specific activity of 226Ra in building materials of operated buildings, a non-destructive in situ method consisted in measurements of gamma spectra with a fixed geometry of the detector position in a room is suggested. The calculation of the average specific activity of natural radionuclides in building materials is carried out by comparing the calculated flux density of unscattered gamma quanta normalized to the specific activity of 100 Bq/kg, and the experimentally measured count rates in the photopeak. For the measured values of the average specific activity of 226Ra in building materials, the expected values of radon concentration in rooms were calculated. The developed method has been verified for rooms in modern multi-storey energy-efficient buildings. Concentrations of 232Th and 40K in building materials which contribute to the indoor external radiation exposure can be measured by developed method also.

Factors influencing radon concentration during energy retrofitting in domestic buildings: A computational evaluation

The findings of recent research signalled increased radon levels following energy retrofitting of dwellings but to date, there have been limited quantitative data to support this observation. A modelling framework was developed that incorporates a dynamic radon entry rate, capturing changes in pressure differentials, to investigate changes in radon concentration following different energy-efficient retrofit measures in naturally-ventilated dwellings. Simulations examined a range of input criteria: dwelling type, air permeabilities, radon flow exponents, pre and post thermal retrofit characteristics, outdoor weather locations and corresponding wind profiles, as well as different ventilation guidelines. A total of 3,780 simulations were carried out. The air permeability of the building had the greatest impact on radon concentration with increases of up to 107%. Non-linear increases were observed arising from the impacts on pressure differentials due to changes in air permeability. The application of representative weather profiles associated with different locations (e.g. coastal, inland) resulted in differences of up to 37%. To a lesser extent, increased indoor temperature due to thermally retrofitting the building fabric, without changes in air permeability, resulted in radon levels increasing by 7%. Additionally, it was shown that the radon flow exponent was not a significant influence on radon concentrations following a retrofit. The addition of ventilation measures means that it is possible to achieve increased airtightness without impacting on the radon concentration. Overall, the simulations provide quantitative information that explains increased airtightness and elevated radon levels, highlighting the potential for radon concentrations to either increase or decrease following an energy retrofit.

An approach to predicting indoor radon concentration based on depressurisation measurements

Exposure to radon is recognised as the second-leading cause of lung cancer after tobacco smoke. The passive measurements typically take up to three months to be representative of the annual radon concentration. A recently developed approach depressurises a dwelling to heighten the convective radon flux determining radon entry rate coefficients. The current study characterises the ventilation status, air tightness and eight selected hourly air change rates measurements, of a sample of naturally ventilated dwellings in Ireland. The household averaged air change rate ranged from 0.28 to 1.87 h−1 and airtightness measurements ranged from 4.830 to 9.423 m3 h−1 m−2 @ 50 Pa, depending on the building characteristics. The experimentally obtained values were used to parameterise a computational model for these selected dwellings and to predict radon concentrations. The radon entry rate power laws ranged from 0.18ΔP0.97 to 1.28ΔP1.18 Bq s−1. Probabilistic functions were generated based on the experimental data and predicted radon concentrations were within one standard deviation of the experimentally measured values in three out of four cases. The data generated can be used in modelling simulations to predict indoor radon concentrations based on local meteorological conditions, building characteristics, ventilation guidelines and energy-retrofit measurements.

Impact of ventilation systems and energy savings in a building on the mechanisms governing the indoor radon activity concentration

For a given radon potential in the ground and a given building, the parameters affecting the indoor radon activity concentration (IRnAC) are indoor depressurization of a building and its air change rate. These parameters depend mainly on the building characteristics, such as airtightness, and on the nature and performances of the ventilation system. This study involves a numerical sensitivity assessment of the indoor environmental conditions on the IRnAC in buildings. A numerical ventilation model has been adapted to take into account the effects of variations in the indoor environmental conditions (depressurization and air change rate) on the radon entry rate and on the IRnAC. In the context of the development of a policy to reduce energy consumption in a building, the results obtained showed that IRnAC could be strongly affected by variations in the air permeability of the building associated with the ventilation regime.

Radon emission rate and analysis of its influencing parameters

Abstract The geological and structural conditions define the radon situation inside a building. While the geological realities can be specified by the content of radium-226 and the ratio of radon-222 emitted from the ground the structural conditions are defined by the tightness of the building envelope. The radon concentration inside has an unsteady character, which is caused by meteorological conditions outside and the air change rate (ACH or ACR), which in turn is influenced by the residents’ behaviour such as venting and heating. For the assessment of the radon exposition, it is necessary to perform measurements for a long time. An approach to reduce this time by eliminating the inhabitants influence on the radon concentration is the radon emission rate, also known as radon entry rate. This variable is based on the measurement of the radon concentration and the parallel determination of the air change rate via a tracer gas method, the result expresses a released activity per time. Due to their noisy character, it is necessary to apply a smoothing algorithm to the input parameters. In addition to mean values, the use of window functions, known from digital signal processing, was analysed. For the verification of the whole calculation procedure, simulations and measurements under defined conditions were used. Furthermore, measurements in an uninhabited house showed proof of the capability of the assessment of the radon potential. First examinations of influencing parameters of the radon emission rate showed a possible dependence on the temperature difference inside and outside the building.

Measurement strategy to study radon source, entry and dilution rates in energy-efficient buildings in Russia

Main physical quantities, which control indoor radon in modern energy-efficient buildings of Russia was studied basing on the results of radon survey in Ekaterinburg, Russia. It was approved that measures to increase energy efficiency lead to reduction in the ventilation rate and high accumulation of radon concentrations indoors. Long-term measurements with application of proposed mathematical methods give an improved understanding of the radon entry processes. Combined use of integrative and time series (differential) measurements provides effective way to develop standard protocol for radon measurements in energy-efficient multi-storey buildings.

Influence of humidity on radon and thoron exhalation rates from building materials

The contributions of radon and thoron from building materials to total radon (thoron) entry rates in dwellings range from almost zero to several percent. It is necessary to measure radon and thoron exhalation rates, among other things, to assess the radiological hazard to human health in a living environment. Brick and granite specimens were used to study the changes of these rates as a function of the relative and absolute humidities. Measurement results showed that radon and thoron exhalation rates change to humidity with the same trends as well as effective dose could be changed by the factor of 2 due to this.

Radon entry rate analyses using in situ tracer gas method application.

Recently, the role of energy savings in indoor air quality deterioration has been extensively emphasised, predominantly in the context of significant air exchange rate reduction as a result of home energy retrofits. In case of refurbishment of existing buildings, the effect of energy-efficient technologies on indoor radon concentration is considerably complex and has to be carefully evaluated with respect to radon entry rate (RER) and air exchange rate alteration. For the purpose of detailed analysis of radon entry pathways, the unique infiltration experiment has been carried out using the tracer gas (N2O) method application in field conditions. Significant amount of experimental works has been done to provide an independent assessment of RER and air-exchange rate facilitating the analysis of fundamental factors influencing the indoor radon variations (e.g. indoor-outdoor pressure difference induced by wind, stack effect, heating, ventilation and operation of air-conditioning systems).

Determination of mechanisms and parameters which affect radon entry into a room

There are practically no direct techniques for measuring radon entry rate in the rooms. The suggested technique allows estimating such parameter under real conditions. The technique for radon diagnostic procedures including radon entry rate and air change rate assessment was proposed and tested in the field under various experimental conditions.The method consists of the continuous measurement of radon concentration, temperature and pressure difference between indoor and outdoor atmosphere. It was demonstrated that the study of dependence of radon entry rate on temperature difference ΔT between indoor and outdoor atmosphere allows to estimate the dominant radon entry mechanism – diffusion mechanism (absence of the dependence on ΔT) or convective (radon entry rate increase at ΔT increase). It was shown that simultaneous measurements of time series of radon concentration and pressure difference between building envelope and outdoor atmosphere allow assessing such room parameter as Effective Leakage Area.The approach applied in this paper to estimate the air change rate practically is not differing from tracer gas techniques when the constant gas entry rate is used. It was shown that radon could be used as kind of tracer gas to estimate the air change rate.Obtained measurement results for all buildings confirmed the seasonal variations of radon concentrations. A correlation of radon concentration and air change rate with outside temperature occurred in general.

Significance of independent radon entry rate and air exchange rate assessment for the purpose of radon mitigation effectiveness proper evaluation: case studies

Two new single-family houses identified as insufficient with regard to existing radon barrier efficiency, have been selected for further examination. A complex set of radon diagnosis procedures has been applied in order to localise and quantify radon entry pathways into the indoor environment. Independent assessment of radon entry rate and air exchange rate has been carried out using the continuous indoor radon measurement and a specific tracer gas application. Simultaneous assessment of these key determining factors has turned out to be absolutely crucial in the context of major cause identification of elevated indoor radon concentration.

State-space dynamic model for estimation of radon entry rate, based on Kalman filtering

To predict the radon concentration in a house environment and to understand the role of all factors affecting its behavior, it is necessary to recognize time variation in both air exchange rate and radon entry rate into a house. This paper describes a new approach to the separation of their effects, which effectively allows continuous estimation of both radon entry rate and air exchange rate from simultaneous tracer gas (carbon monoxide) and radon gas measurement data. It is based on a state-space statistical model which permits quick and efficient calculations. Underlying computations are based on (extended) Kalman filtering, whose practical software implementation is easy. Key property is the model's flexibility, so that it can be easily adjusted to handle various artificial regimens of both radon gas and CO gas level manipulation. After introducing the statistical model formally, its performance will be demonstrated on real data from measurements conducted in our experimental, naturally ventilated and unoccupied room. To verify our method, radon entry rate calculated via proposed statistical model was compared with its known reference value. The results from several days of measurement indicated fairly good agreement (up to 5% between reference value radon entry rate and its value calculated continuously via proposed method, in average). Measured radon concentration moved around the level approximately 600 Bq m −3, whereas the range of air exchange rate was 0.3–0.8 (h −1).

Cost assessment of ventilation and averted dose due to radon in dwellings

The inhalation dose due to radon and its progenies could be averted by ventilation in dwellings; however, on the other hand the increased ventilation augments the heating cost. Therefore a cost–benefit analysis could contribute to optimise the ventilation rate. In our current work we applied our former defined parameters of the optimising procedure to assess the optimised ventilation and radon concentration in dwellings with average parameters. To assess the inhalation dose rates the time-dependent concentrations of all the progenies were calculated in case of periodic and continuous ventilation as well, at three different radon entry rates (5, 10, 20 kBq h −1). The optimal ventilation rates in case of continuous ventilation are 0.22, 0.40 and 0.66 h −1, respectively. By these conditions the optimal radon concentration takes 160–210 Bq m −3. According to the more detailed analysis the periodic ventilation gives, in general, a better solution than the continuous one. The Monte Carlo simulations provided a large uncertainty; therefore, before the practical application of the results the uncertainty should be decreased taken into account the local conditions.

Effect of various factors on the rate of radon entry into two different types of houses

Various factors that affect the rate of radon entry were investigated in two detached hill-side houses. In the slab-on-grade house (A), this rate reached its maximum value during a particular weather condition when the wind-induced internal transport of radon, whereas the rate of radon entry into the basement house (B) on the upper slope of a esker was highest when the wind was blowing towards the esker. In neither house did changes in barometric pressure measured at 3 h intervals influence the radon entry rate. Nor did rain influence the rate of radon entry into house A. In house A, the radon entry rate was observed to have a 2–3 h delay; and after it was adjusted by the analysis of covariance, the radon entry rate was higher in the morning and lower in the evening. In house B, however, diurnal variations in the radon entry rate were negligible.

Variation of radon entry rate into two detached houses

The influence of various factors on the concentration of indoor and its variation were investigated statistically in two different types and location of houses. In the single-storey slab-on-grade house (A), the variation of indoor radon closely followed the difference in indoor–outdoor temperature. The measured pressure difference across the wall and wind speed were significant variables ( p<0.00), but these factors explained the variation of the radon concentration only slightly. In the two-storey hillside basement house (B), the most significant variable difference in indoor-attic space explained 28% of the variation of the indoor radon. In both houses, the coefficient of determination increased slightly when the average wind speed increased, but in house B the coefficient decreased with high wind speed. In house A, the highest concentration of indoor radon was observed as the wind-induced internal transport of radon. In house B, the highest concentration of indoor radon occurred and the highest coefficient of determination (100 R 2%=89%) was observed when the wind was blowing towards the slope-side of the esker, causing increased soil gas pressure and air flow in soil. According to this study, the effect of the wind speed on the concentration of indoor radon and on the coefficient of determination was difficult to foresee because the effect of the wind on soil depended strongly on the wind direction and location of the houses.

Behaviour of radon, radon progenies and particle levels during room depressurisation

The aim of the study was to investigate the effect of room depressurisation (up to −28 Pa) on indoor radon, radon progenies and particle concentrations in a wooden school building (A) and in a wooden double-family house (B). The airborne concentrations of particles, radon, and radon progenies decreased with increased depressurisation. At the same time, the air exchange rates increased by a factor of 9.5 (house A) and 13 (house B). The calculated radon entry rates thus rose almost in the same ratio, 6.3 and 12, respectively. The equilibrium factors between radon progenies and radon were the same before and after the depressurisation being 0.04 in house A and 0.16 in house B. When the pressure was the lowest, radon concentrations decreased by a factor of 0.7 in house A and 0.9 in house B, and the radon progeny levels fell by a factor of 0.6 in both houses. The particle levels (particles exceeding 0.01 μm) decreased by a factor of 10 (house A) and of 1.2 (house B). The dilution by outdoor air was more effective in house A, which was less tight.

Effects of variable wind speed and direction on radon transport from soil into buildings: model development and exploratory results

We describe a novel modeling technique, based on Duhamel’s theorem, to study the effects of time-varying winds on radon transport in soil near buildings. The technique, implemented in the model RapidSTART, reduces computational times for transient, three-dimensional, wind-induced soil-gas and radon transport by three to four orders of magnitude compared with conventional finite-difference models. To test model performance, we compared its predictions to analytical solutions of one-dimensional soil-column flow, finite-difference simulations of flow around a full-scale house, and measurements of transient soil–gas and radon entry into an experimental basement structure. These comparisons demonstrate that RapidSTART accurately simulates time-dependent radon transport through soil and its entry into buildings. As demonstrated in a previous study, steady winds can significantly affect radon entry. In this paper, we extend the findings of that study by applying RapidSTART to explore the impacts of fluctuating wind speed and direction on radon entry into a prototypical house. In soils with moderate to high permeability, wind fluctuations have a small to moderate effect on the soil-gas radon concentration field and entry rate into the building. Fluctuating wind direction dominates the impact on radon entry rates, while fluctuating wind speed has little effect. For example, in a soil with a permeability of 10 -10 m 2, diurnal oscillations in wind direction can increase the predicted radon entry rate by up to 30% compared to steady-state predictions.

Radon and Natural Ventilation in Newer Danish Single-Family Houses

Abstract To investigate the effect of ventilation on indoor radon (222Rn), simultaneous measurements of radon concentrations and air change rates were made in 117 Danish naturally ventilated slab-on-grade houses built during the period 1984–1989. Radon measurements (based on CR-39 alpha-track detectors) and air change rate measurements (based on the perfluorocarbon tracer technique; PFT) were in the ranges 12–620 Bq m−3 and 0.16−0.96 h−1, respectively. Estimates of radon entry rates on the basis of such time-averaged results are presented and the associated uncertainty is discussed. It was found that differences in radon concentrations from one house to another are primarily caused by differences in radon entry rates whereas differences in air change rates are much less important (accounting for only 80,0% of the house-to-house variation). In spite of the large house-to-house variability of radon entry rates it was demonstrated, however, that natural ventilation does have a significant effect on the indoor radon concentration. Most importantly, it was found that the group of houses with an air change rate above the required level of 0.5 h−1 on average had an indoor radon concentration that was only 50% (0.5±0.1) of that of the group of houses with air change rates below 0.5 h−1. The reducing effect of increased natural ventilation on the indoor radon concentration was found to be due mainly to dilution of indoor air. No effect could be seen regarding reduced radon entry rates.