Indoor Radon Measurements Research Articles

Indoor Radon Monitoring and Associated Diffuse Radon Emissions in the Flanks of Mt. Etna (Italy)

Between October 2021 and July 2024, radon measurements in air and soil were carried out in the South and East flanks of Etna volcano to check the possible correlation between radon emissions and active faults/eruptive fissures and to obtain preliminary data on any negative impacts on human health. Fifteen continuous indoor radon monitors were installed in homes, some of which are inhabited by patients suffering from Multiple Sclerosis and Amyotrophic Lateral Sclerosis. In all sites, the limit of 300 Bq/m3 indicated by the Euratom Directive 2013/59 was exceeded, even if slightly and for short periods. The highest values were recorded closest to active fault zones and during winters. Furthermore, 27 discrete indoor radon measurements were carried out using a passive method by means of activated charcoal canisters that were exposed for 48 h. Most of the values (>70%) were <100 Bq/m3; six canisters gave values >100 Bq/m3 and one >200 Bq/m3. Measurements of radon in soils were carried out using a Durridge RAD7 in the gardens of the homes in which the indoor radon measurements were made. The background radon values in soils were <5000 Bq/m3; the highest values (12,500 Bq/m3) were measured near the Aci Catena fault. The role of Etna’s faults in draining the deeper radon towards the surface and, therefore, into nearby homes is evident, with a consequent increase in the health risk caused by indoor radon pollution.

Indoor radon trends with building code change in two Canadian cities

Radon studies were conducted in two Canadian cities, in Halifax, Nova Scotia, and Winnipeg, Manitoba, to evaluate trends in indoor radon before and after the 2010 National Building Code of Canada was adopted into the legally binding provincial building codes in 2011. Participants were recruited in neighbourhoods characterized by newer housing developments. A postcard campaign in each city offered free radon testing to every house in the target areas, and free testing kits were mailed to study participants. Indoor radon measurements and house questionnaires were completed by 225 eligible participants in Halifax and 171 eligible participants in Winnipeg, using alpha-track radon detectors deployed for three months during the heating season in 2021–2022. Multivariate logistic regression analyses were conducted to evaluate the association between indoor radon and the period of construction, the area in contact with the ground, the number of storeys, the type of heating system, the water source, and the type of ventilation. These analyses were focussed on the detached study houses because the majority of the participants lived in a detached house, and significant associations were identified for the period of construction and the floor where the radon detector was located. An odds ratio of 1.91 (1.04–3.50) for the detached Halifax study houses built after 2011 was associated with having a higher than geometric mean radon concentration (p = 0.033), nearly double the likelihood. There was no evidence of significant change in the indoor radon after 2011 in the detached Winnipeg study houses. A lower likelihood – almost half - for measurement conducted on a main/upper floor compared to in the basement was associated with a radon concentration above the respective geometric mean for each city: an odds ratio of 0.48 (0.27–0.86) for the detached Halifax study houses (p = 0.012), and of 0.45 (0.32–0.64) for the detached Winnipeg study houses (p = 0.022). Radon is the second most important cause of lung cancer, after smoking, and the results of this study support strengthening the radon preventive measures required in new low-rise housing to reduce the associated lung cancer burden in Canada.

Utilization of radiometric data for mapping primary and secondary sources of gamma radiation and radon/thoron release potentials in Ireland.

This paper presents a novel approach to predict and map radon and thoron levels. We developed separate radon and thoron prediction maps for Ireland and introduced a system for producing high-resolution 3D radiation maps which may be used for planning purposes in residential areas, recycling and demolishing waste depots, and quarries of building and construction material. Additionally, we highlight the critical need to monitor thoron alongside radon in indoor surveys, as thoron's shorter half-life and higher energy levels may pose a greater health risk. We utilized Tellus radiometric survey data and indoor radon measurement records to investigate the spatial correlation between elevated indoor radon activity and anomalies in radioelement concentrations. We also estimated the degree of thoron interference in indoor radon surveys conducted in Ireland using CR-39 detectors. Field and laboratory surveys were performed to produce high-resolution radiation maps for four Irish quarries and estimate the radon and thoron potential of these quarries. Our initial findings suggest that thoron may be the primary health issue in some parts of Ireland, surpassing radon. For example, our map shows that the expected thoron potential in county Donegal is significantly higher than that for radon. Our radon and thoron exhalation tests on building material samples from four random quarries confirm this. We also estimate that over 20% of the elevated indoor radon activity recorded by the EPA using CR-39 detectors may be attributed to thoron-related sources. This study contributes to a better understanding of the prevalence and impact of radon and thoron in Ireland, helping to determine the main radiological health issue related to indoor air quality in the country. Thoron's impact on indoor air quality and health has been understudied in Ireland, necessitating more comprehensive studies and monitoring programs to accurately assess the prevalence and impact of both radon and thoron.

Spatial multi-criteria approaches for estimating geogenic radon hazard index

The geogenic radon hazard index (GRHI) map plays a crucial role in evaluating radon exposure risks. The construction of this map requires a comprehensive analysis of radon levels in soil gas and some critical factors, such as uranium content in bedrock, soil permeability, and geological inhomogeneities. In this context, the spatial multi-criteria decision analysis is proposed to integrate the GRHI-based criteria for identifying the high-potential radon areas. In particular, the multivariate integration involves the fuzzy gamma operator and a hybrid multi-criteria decision-making technique, namely AHP-TOPSIS, which represents a novel approach in GRHI mapping. Thus, a comparison is provided through the definition of the GRHI map of an unexplored study area, that is the Apulia region, located in Southern Italy. In order to evaluate the output maps, high radon potential areas are identified based on some available indoor radon measurement data. The success-rate curve, as a valid evaluation metric, is employed for the performance assessment and comparison of these two methods. The results demonstrate that although both generated GRHI maps are closely correlated with high-potential radon zones in Apulia, the hybrid AHP-TOPSIS method is preferable in identifying areas with elevated radon potential.

Strategy and Metrological Support for Indoor Radon Measurements Using Popular Low-Cost Active Monitors with High and Low Sensitivity.

Traditionally, for indoor radon testing, predominantly passive measurements have been used, typically applying the solid-state alpha track-etch method for long-term and the charcoal method for short-term measurements. However, increasingly, affordable consumer-grade active monitors have become available in the last few years, which can generate a concentration time series of an almost arbitrary duration. Firstly, we argue that consumer-grade monitors can well be used for quality-assured indoor radon assessment and consequent reliable decisions. Secondly, we discuss the requirements of quality assurance, which actually allow for reliable decision-making. In particular, as part of a rational strategy, we discuss how to interpret measurement results from low-cost active monitors with high and low sensitivity with respect to deciding on conformity with reference levels that are the annual average concentration of indoor radon. Rigorous analysis shows that temporal variations in radon are a major component of the uncertainty in decision-making, the reliability of which is practically independent of monitor sensitivity. Manufacturers of low-cost radon monitors already provide sufficient reliability and quality of calibration for their devices, which can be used by both professional inspectors and the general public. Therefore, within the suggested measurement strategy and metrologically assured criteria, we only propose to clarify the set and values of the key metrological characteristics of radon monitors as well as to upgrade user-friendly online tools. By implementing clear metrological requirements as well as the rational measurement strategy for the reliable conformity assessment of a room (building) with radon safety requirements, we anticipate significant reductions in testing costs, increased accessibility, and enhanced quality assurance and control (QA/QC) in indoor radon measurements.

Short-Term vs. Long-Term: A Critical Review of Indoor Radon Measurement Techniques.

Radon is a known carcinogen, and the accurate assessment of indoor levels is essential for effective mitigation strategies. While long-term testing provides the most reliable data, short-term testing (STT) offers a quicker and more cost-effective alternative. This review evaluated the accuracy of STT in predicting annual radon averages and compared testing strategies in Europe (where long-term measurements are common) and the United States (where STT is prevalent). Twenty (20) studies were systematically identified through searches in scientific databases and the grey literature, focusing on STT accuracy and radon management. This review revealed several factors that influence the accuracy of STT. Most studies recommended a minimum four-day test for initial screening, but accuracy varied with radon levels. For low levels (<75 Bq/m3), a one-week STT achieved high confidence (>95%) in predicting annual averages. However, accuracy decreased for moderate levels (approximately 50% success rate), necessitating confirmation with longer testing periods (3 months). High radon levels made STT unsuitable due to significant fluctuations. Seasonality also played a role, with winter months providing a more representative picture of annual radon averages. STT was found to be a useful method for screening low-risk areas with low radon concentrations. However, its limitations were evident in moderate- and high-level scenarios. While a minimum of four days was recommended, longer testing periods (3 months or more) were crucial for achieving reliable results, particularly in areas with potential for elevated radon exposure. This review suggests the need for further research to explore the possibility of harmonizing radon testing protocols between Europe and the United States.

Indoor Radon Measurement in Buildings of A.O.R.N Cardarelli, the Largest Hospital of National Relevance in Southern Italy

: Indoor radon concentrations constitute a major source of exposure to ionizing radiation for humans. It has been estimated that radon contributes about 10% of deaths from lung cancer in the USA and Europe. In Italy, current legislation establishes that the concentration of radon must be monitored in all workplaces located in a basement and on the ground floor. In this study, the indoor radon concentration of 20 multi-floor buildings on the Cardarelli Hospital was measured during two consecutive semesters. The survey was carried out with CR-39 solid-state nuclear track detectors (SSNTDs). Radon concentrations were found to range from 4 Bq/m3 to 424 Bq/m3, with a median of 24 Bq/m3. The dependence of the radon concentrations on the measurement floor and the room-to-room spatial variation was also analyzed.

Assessment of soil moisture on radon levels, radon exhalation, natural radioactivity, and radiological risks in offices and laboratories in GAEC

This study investigates the influence of moisture on soil radon exhalation, natural radioactivity in soil, and indoor radon concentrations in offices and laboratories at the Ghana Atomic Energy Commission (GAEC) and their associated radiological risks to workers. Radon exhalation rates were determined using the Sealed Can method. CR-39 SSNTD detectors were used to measure indoor radon concentrations. Gamma spectroscopy using HpGe detector was used to determine the activity concentrations of U-238, Ra-226, Th-232, and K-40 in the soil samples. The results showed mean concentrations of 14.3 ± 2.0 Bq/kg (CI 95%: 10.0–18.0) for U-238, 145.0 ± 10.0 Bq/kg (CI 95%:123.0–167.0) for K-40, 31.5 ± 6.0 Bq/kg (CI 95%: 24.0–39.0) for Th-232, and 15.6 ± 2.0 Bq/kg (CI 95%:14.0–29.0) for Ra-226. The results showed mean surface and mass exhalation rates of 6.9 ± 2.3 × 10−4 Bq/m2/h1 (CI 95%: 5.7 × 10−4 –12.6 × 10−4) and 2.4 ± 0.4 (CI 95%: 1.9–4.2) nBq/kg1/h1 respectively. The findings revealed mean indoor radon concentrations of 93.0 ± 10.0 Bq/m3 (CI 95%: 88.0–98.0), 111.0 ± 12.0 Bq/m3 (CI 95%: 102.0–119.0) and 145.0 ± 13.0 Bq/m3 (CI 95%: 135.0–155.0) in the offices, laboratories, and basements respectively, with laboratories and basements exceeding the WHO reference level of 100 Bq/m3. A strong inverse relationship between moisture levels and exhalation rates (r = −0.8) was observed, leading to a negative correlation (r = −0.3). Between the moisture levels and indoor radon levels. The research findings indicated a mean annual effective dose of 0.6 mSv/yr. (CI 95%: 0.5–0.6) to the workers, which is well below occupational and public dose limits. The lung cancer cases of workers were computed which ranged from 0.9 × 10−8 to 1.2 × 10−8 cases per million people per year, which is less than the limit range of 170–230 per million people per year recommended by ICRP but remaining with safe radiological limits for workers. This study identified moderate radon exposure risks at the GAEC, exceeding the WHO recommendation. The correlation and trend analysis demonstrate strong relationships between moisture, exhalation rates, radium, and indoor radon.

Assessment of Indoor and Water Radon Concentrations in Esenyurt and Beylikdüzü Districts of Istanbul, Marmara Region, Turkey

The radon activity concentration measurements for indoor and tap water were studied in Esenyurt and Beylikdüzü districts of Istanbul Province, Turkey. The mean radon concentration value received from thirty-six passive radon detectors was obtained as 63.56 Bq/m3. The mean annual effective dose for indoor radon measurements is 1.60 mSv/y in this measurement period. The radon activity results of calculated tap water samples were under 0.8 Bq/L. The annual effective doses resulting from ingestion and inhalation were calculated to evaluate the health risk across various age groups. All radon measurement results, and the associated calculated data for ingestion and inhalation remained below the threshold values established by international organizations

The BC Radon Data Repository (BCRDR) and BC Radon Map: Integrating disparate data sources for improved public health communication.

The potential for exposure to indoor radon varies dramatically across British Columbia(BC) due to varied geology. Individuals may struggle to understand their exposure risk and agencies may struggle to understand the value of population-level programs and policies to mitigate risk. The BC Centre for Disease Control (BCCDC) established the BC Radon Data Repository (BCRDR) to facilitate radon research, public awareness, and action in the province. The BCRDR aggregates indoor radon measurements collected by government agencies, industry professionals and organizations, and research and advocacy groups. Participation was formalized with a data sharing agreement, which outlines how the BCCDC anonymizes and manages the shared data integrated into the BCRDR. The BCRDR currently holds 38,733 measurements from 18 data contributors. The repository continues to grow with new measurements from existing contributors and the addition of new contributors. A prominent use of the BCRDR was to create the online, interactive BC Radon Map, which includes regional concentration summaries, risk interpretation messaging, and health promotion information. Anonymized BCRDR data are also available for external release upon request. The BCCDC leverages existing radon measurement programs to create a large and integrated database with wide geographic coverage. The development and application of the BCRDR informs public health research and action beyond the BCCDC, and the repository can serve as a model for other regional or national initiatives.

Кризис регулирования радона в России: масштаб проблемы и предложения по исправлению

Among the many accumulated challenges, radon mitigation measures for existing buildings are not still carried out in Russia that, combined with the use of an inadequate method for indoor radon measurements, has led to stagnation and crisis of the radon regulation system. To overcome the crisis, a ranking of buildings and responsibility distribution in radon control, including theses on updating the national norms and regulations for ensuring radiation safety, as well as nine priority activities of the radon action plan are proposed in accordance with IAEA requirements.

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.

Indoor radon and thoron levels in some residences of Sri Renga Narayana Puram Village, Tirunelveli, India, using solid-state nuclear track detectors

The indoor radon and thoron measurements were carried out at Sri Renga Narayana Puram village, Tirunelveli district, Tamil Nadu, which is located nearer to the Nuclear Power Plant, Kudankulam. The survey was performed using a single-entry pin-hole dosimeter with a solid-state nuclear track detector for a period of 90 days. In the present study, the radon and thoron levels have been measured initially for 10 residences using LR-115 Type II films as a detector. The dose assessment due to radon and thoron is calculated. The effective dose of radon and thoron in the corresponding residences has been found to vary from 0.516 to 0.660 mSvy−1 and 0.010 to 0.144 mSvy−1. The total effective dose due to radon and thoron has been calculated which found to vary from 0.545 to 0.791 mSvy−1 with an average value of 0.655 mSvy−1.

Standardization of indoor radon measurements based on rational criterion for conformity assessment

Significant temporal variations in radon are observed in any buildings, including unoccupied buildings with limited ventilation. This fact causes serious difficulties in radiation monitoring to assess the compliance of premises with the requirements of the normative, which limits the annual average level of radon in buildings. Therefore, neither at the national nor at the international level has yet been solved the problem of standardizing the indoor radon measurement if the test duration is less than a year. An analysis of approaches to radon measurement, including an assessment of the effectiveness of regulation, shows very significant differences between practices established in different countries. For example, in Russia, rapid (no more than 20 min) measurements are mainly used and mitigation measures to protect existing buildings from radon are practically not carried out. In European countries, mainly long-term (at least two months) measurements are used, while mitigation measures are still relatively rare, with the exception of the UK and Sweden. In the USA, short-term (2–7 days) measurements are widely used, which are not only carried out, but also paid for by residents themselves, including mitigation measures. However, despite the established approaches to indoor radon monitoring in Russia and the USA, there is a persistent distrust among specialists in the results of shortterm and, especially, rapid measurements. In this regard, a compromise approach is proposed to standardize radon measurements based on a rational criterion by applying fundamental ISO/IEC concepts such as “measurement uncertainty” and “conformity assessment”. The rational criterion for conformity assessment allows using measurements of different durations, providing a given reliability when making a decision. It also proposes a rationale for optimizing indoor radon monitoring through the participation of not only professional inspectors, but also the population itself due to the possibility of introducing simple methods and inexpensive radon devices within the rational criterion.

Assessment of Radon and Naturally Occurring Radionuclides in the Vredefort Meteorite Crater in South Africa

The concentric impact rings of the Vredefort Crater contain rocks with elevated uranium concentrations resulting from the geological signature of a meteoric impact. The decay of this uranium was estimated to lead to elevated indoor radon concentrations in the Crater, but such a study has never been carried out. This study explores the relationship between the natural radionuclides found in the geology of the Vredefort Crater and indoor radon concentrations. This was achieved through soil sampling and radionuclide surveys conducted on three impact rings, supplemented by indoor radon measurements in dwellings found in the area. In situ measurements revealed that one impact ring had higher-than-average uranium concentrations at 50 Bq/kg. Surprisingly, the measured indoor radon levels were lower than expected (113 Bq/m3). These measurements were taken during the COVID-19 pandemic and colder months, conditions that would typically result in elevated indoor radon levels. Soil samples indicated uranium activity of 30 Bq/kg, comparable to the world average of 35 Bq/kg. However, defunct mine tunnels in the area exhibited elevated radon concentrations, averaging 364 Bq/m3. The disparity between expected and measured indoor radon levels was attributed to the composition of surficial deposits, bedrock, and architectural features of the dwellings preventing radon accumulation.

Evaluating the indoor radon concentrations in the Swedish building stock using statistical and machine learning

Exposure to excessive indoor radon causes around 500 lung cancer deaths in Sweden annually. However, until 2020, indoor radon measurements were only conducted in around 16% of Swedish single-family houses and 17% of multifamily houses. It is estimated that approximately 16% of single-family houses exceed the indoor radon reference level of 200 Bq/m3, and the corresponding situation in multifamily houses is unknown. Measuring indoor radon on an urban scale is complicated and costly. Statistical and machine learning, exploiting historical data for pattern identification, provides alternative approaches for assessing indoor radon risk in existing dwellings. By training MARS (Multivariate Adaptive Regression Splines) and Random Forest (RF) regression models with the data labels from the radon measurement records in the Swedish Energy Performance Certification registers, property registers, soil maps, and the radiometric grids, the correlations between response and predictive variables can be untangled. The interplay of the key features, including uranium and thorium concentrations, ventilation systems, construction year, basements, and the number of floors, and their impact magnitudes on indoor radon concentrations, are investigated in the study. The regression models tailored for different building classes were developed and evaluated. Despite the data complexity, the RF models can explain 28% of the variance in multifamily houses, 24% in all buildings, and 21% in single-family houses. To improve model fitting, more intricate supervised learning algorithms should be explored in the future. The study outcomes can contribute to prioritizing remediation measures for building stocks suspected of high indoor radon risk.

Estimation of radiation dose due to thoron and progeny inhalation in high background natural radiation area of Odisha, India

Abstract Results of the preliminary measurements of indoor radon, thoron and progeny concentrations showed very high values of thoron concentrations in the eastern coastal region of Odisha, India. Therefore, measurements of thoron and its progeny concentrations were extended to a larger number of houses in this area for the assessment of the radiation dose received by the public. The measured values of thoron concentrations were used for the calculation of annual effective doses. The estimated values of the annual effective dose due to thoron exposure were observed in the range of 0.2–14.7 mSv. The estimated radiation doses responsible for thoron exposure were observed considerably high in the region. The results obtained are compared with those obtained in other studies performed so far in the study area and a review of different studies involving different measurement techniques is presented in the paper. The results of this study support the preliminary studies showing high values of thoron levels in the study area.

Exploring assumptions for air infiltration rate estimates using indoor radon in UK homes

Radon, a known carcinogen, is one of the most commonly monitored indoor contaminants. This paper utilises findings from a previous study on indoor radon measurements in United Kingdom (UK) homes to explore the UK Government’s Standard Assessment Procedure (SAP) assumptions for air infiltration rates. These assumptions are important as they are used to assess the energy performance of dwellings and compliance with building regulations. Indoor radon data is aggregated by 16 combinations of home energy efficiency measures (loft and wall insulation, glazing upgrades and draught proofing) and fitted using a simple analytic radon model. We find indoor radon to be inversely proportional to air change rate and proportional to a fit coefficient, k, of 42.2 ± 3.1 (95% Confidence Interval (CI)). We also show that the assumptions within SAP used to estimate home infiltration rates can be modified to include the impact of home energy efficiency which improves the fit (R 2 from 0.38 to 0.51) to the radon data. This work provides evidence to help improve assumptions regarding the effects of home energy efficiency on infiltration rates.

Development of a Pre-Diagnosis Procedure for the Evaluation of Indoor Radon Potential in Buildings

Indoor radon accumulation is considered the main source of human exposure to ionizing radiation. Depending on the average radon level, indoor long-term exposure can significantly increase the risk of lung cancer onset. The publication of international regulations on the protection of human health the exposure of ionizing radiation, defining threshold values over whom health consequences for occupants could be expected, led to the control and testing of radon levels in workplaces and premises using multiple techniques and approaches. In particular, since the main source of radon is soil, many efforts have been done for the redaction of maps of the geogenic potential risk, as well as the definition of proper measurement standards and techniques for indoor monitoring. Radon maps, based on geology and measurements of radon and/ or the natural radioactive content in the soil, constitute an evaluable tool for decision-making authorities in radon policies giving the possibility to characterize areas for radon risk where indoor radon measurements are not available. But, of course, they are not completely descriptive of the potential risk, so indoor monitoring in buildings is also required. The correct design of an indoor monitoring campaign is a crucial topic.. Scientific literature has largely demonstrated that many site-specific features influence the accumulation process, as well as most building materials represent a significant source, after the soil. The preliminary complete investigation in buildings should be properly defined since radiation safety in a situation of radon exposure completely ensured during the building's construction and maintenance phases as well as during the selling/rental ones. So, the aim of this work is to put the basis for the development of a pre-diagnosis procedure as a tool for the screening of buildings susceptible to high indoor radon activity concentrations. The work represents a very early stage of implementation of a qualitative method for the design of a measurement campaign for the indoor radon assessment. A pre-evaluation selection of the variables that play a leading role in the accumulation process is presented. A prior survey, based on evidence in scientific literature, was done to identify all relevant characteristics that most affect indoor radon levels, mainly concerning local geology, building features, ventilation, and occupancy factors. The selected parameters, classified into levels according to defined indicators and then combined, allow a more refined sample selection for measurements campaign in the indoor radon assessment process. Future development will be oriented to the validation of case studies and the implementation of the procedure in a software environment which will be the first tool available to systematize and regulate the radon monitoring process for short-term decision-making.

Indoor radon concentration levels in some selected offices at Ibrahim Badamasi Babangida University, Lapai, Nigeria and its attendant annual effective dose

Although radon concentrations in outdoor environments are generally low, the indoor concentrations can become appreciably high thereby affecting the indoor air quality and causing some severe health challenges. Thirty (30) offices from the ground floor and first floor of some buildings within Ibrahim Badamasi Babangida (IBB) University campus, Lapai Nigeria, were randomly selected for indoor radon concentration (CRn) measurement using RAD7 continuous radon monitor. Annual effective dose was also computed to determine the level of public exposure. The results showed that radon concentration values for all the offices on the ground floor ranged between 9.6±2.7 Bqm−3 and 90.7±8.1 Bqm−3, with mean value of 28.5±4.8 Bqm−3 while the range of radon concentration at first floor was 2.5±1.4 Bqm−3 - 80.4±7.5 Bqm−3. All the measured indoor radon concentration levels were less than the 100 Bqm−3 action level proposed by World Health Organization (WHO). Average annual absorbed dose for both ground and first floors were 0.36±0.06 mSvy−1 and 0.24±0.05 mSvy−1 respectively, with corresponding mean annual effective dose of 0.86±0.15 mSvy−1 and 0.58±0.11 mSvy−1 in sequence. These values were below the 1.0 mSvy−1 safety limit set for public. Although the results did not suggest any immediate exposure threat to the public, it is important that the University staffs are adequately informed of indoor radon levels and its attendant health hazards. Improved and adequate ventilation of all the office buildings is highly encouraged in order to keep the radon levels as low as reasonably achievable (ALARA).