A Comparative Study of Indoor Radon Levels between Two Similar Dwellings Using CONTAM Software

Assessing the effects of transient weather conditions on airborne transmission risk in naturally ventilated hospitals

BACKGROUND

Many UK hospitals rely heavily on natural ventilation as their main source of airflow in patient wards. This method of ventilation can have cost and energy benefits, but it may lead to unpredictable flow patterns between indoor spaces, potentially leading to the unexpected transport of infectious material to other connecting zones. However, the effects of weather conditions on airborne transmission are often overlooked.

METHODS

A multi-zone CONTAM model of a naturally ventilated hospital respiratory ward, incorporating time-varying weather, was proposed. Coupling this with an airborne infection model, this study assessed the variable risk in interconnected spaces, focusing particularly on occupancy, disease and ventilation scenarios based on a UK respiratory ward.

RESULTS

The results suggest that natural ventilation with varying weather conditions can cause irregularities in the ventilation rates and interzonal flow rates of connected zones, leading to infrequent but high peaks in the concentration of airborne pathogens in particular rooms. This transient behaviour increases the risk of airborne infection, particularly through movement of pathogens between rooms, and highlights that large outbreaks may be more likely under certain conditions. This study demonstrated how ventilation rates achieved by natural ventilation are likely to fall below the recommended guidance, and that the implementation of supplemental mechanical ventilation can increase ventilation rates and reduce the variability in infection risks.

CONCLUSION

This model emphasises the need for consideration of transient external conditions when assessing the risk of transmission of airborne infection in indoor environments.

Analysis of Ventilation Efficiency as Simultaneous Control of Radon and Carbon Dioxide Levels in Indoor Air Applying Transient Modelling

The impact of ventilation efficiency on radon (²²²Rn) and carbon dioxide (CO₂) concentrations in the indoor air of a residential building was studied by applying transient data analysis within the CONTAM 3.4 program. Continuous measurements of ²²²Rn and CO₂ concentrations, together with basic meteorological parameters, were carried out in an apartment (floor area about 27 m²) located in Ljubljana, Slovenia. Throughout the experiment (October 3–15), frequent ventilation (several times per day), poor ventilation (once to twice per day) and no ventilation scenarios were applied, and the exact ventilation and occupancy schedule were recorded. Based on the measurements, a transient simulation of ²²²Rn and CO₂ concentrations was performed for six sets of scenarios, where the design ventilation rate (DVR) varied based on the ventilation requirements and recommendations. On the days of frequent ventilation, a moderate correlation between the measured and simulated concentrations (r = 0.62 for ²²²Rn, r = 0.55 for CO₂) was found. The results of the simulation indicated the following optimal DVRs: (i) 36.6 m³ h⁻¹ (0.5 air changes per hour, ACH) to ensure a CO₂ concentration below 1000 ppm and a ²²²Rn concentration below 100 Bq m⁻³; and (ii) 46.9 m³ h⁻¹ (0.7 ACH) to ensure a CO₂ concentration below 800 ppm. These levels are the most compatible with the 5C_Cat I (category I of indoor environmental quality, defined by EN 16798-1:2019) scenario, which resulted in concentrations of 656 ± 121 ppm for CO₂ and 57 ± 13 Bq m⁻³ for ²²²Rn. The approach presented is applicable to various types of residential buildings with high overcrowding rates, where a sufficient amount of air volume to achieve category I indoor environmental quality has to be provided. Lower CO₂ and ²²²Rn concentrations indoors minimise health risk, which is especially important for protecting sensitive and fragile occupants.

Determination of optimal ventilation rates in educational environment in terms of radon dosimetry

INTRODUCTION

New and renovated energy efficient buildings with minimised ventilation rates together with increased building airtightness are often associated with higher indoor radon concentrations compared to the concentrations in existing buildings. The purpose of our study is to analyse the problem associated with the increased radon concentration and ventilation requirements and recommendations in schools. The radon concentration was critically assessed by varying the design ventilation rates (DVRs) within fifteen cases according to legislative requirements and recommendations. The case study is a branch primary school in western part of Slovenia situated in a radon prone area.

METHODS

Radon (²²²Rn) concentrations were simulated in the classroom, using CONTAM 3.2.

PROGRAM

For validation, measurements were performed on 8 measuring days in September and 6 measuring days in March. The simulated and measured ²²²Rn concentrations are well correlated for all measurement days, with the simulated/measured ratio of 0.85-1.39. In order to define optimal DVRs in terms of dosimetry, the effective dose and its ratio to the worldwide average effective dose at workplace, received by radon progeny in 950 h (expected effective dose, 0.13 mSv/y), were calculated for each case.

RESULTS

Simulations showed that the highest radon concentrations were observed in case 1 with a DVR of 79.6 m³/h (621 Bq/m³) and case 4 with a DVR of 69.4 m³/h (711 Bq/m³), both defined by national regulations. The calculated values in both cases exceeded the national reference value for radon (300 Bq/m³) by 2.1 times and 2.4 times, and the WHO guideline value (100 Bq/m³) by 6.2 times and 7.1 times, respectively. The simulations are in line with the results of radon dosimetry. Both DVRs correspond to the highest effective doses, 1.88 mSv/y (about 14-fold higher than expected effective dose) for case 1 and 2.15 mSv/y (about 17-fold higher than expected effective dose) for case 4. Case 11_Cat I with a DVR of 1999.7 m³/h defined by EN 15251: 2007 resulted in minimal Rn concentration (35 Bq/m³) and corresponds to the lowest effective dose 0.11 mSv/y and its ratio to the expected effective dose 0.8.

CONCLUSIONS

Ventilation is an immediate measure to reduce radon concentration in a classroom and it must be performed in line with other holistic measures to prevent and control radon as a health risk factor.