Radon and thoron concentrations in public workplaces in Brisbane, Australia

• Radon and thoron concentrations in public workplaces in Brisbane city were measured.
• The average radon and thoron concentrations were 10.5 ± 11.3 and 8.2 ± 1.4 Bq m−3.
• Radon and thoron levels were relatively higher in the storage rooms and basements.
• A diurnal variation was observed in the radon concentration in most locations.
• Radon and thoron concentrations tended to be higher in rooms with concrete flooring.

Radon and thoron are radioactive gases that can emanate from soil and building materials, and it can accumulate in indoor environments. The concentrations of radon and thoron in the air from various workplace categories in Brisbane, Australia were measured using an active method. The average radon and thoron concentrations for all workplace categories were 10.5 ± 11.3 and 8.2 ± 1.4 Bq m−3, respectively. The highest radon concentration was detected in a confined area, 86.6 ± 6.0 Bq m−3, while the maximum thoron level was found in a storage room, 78.1 ± 14.0 Bq m−3. At each site, the concentrations of radon and thoron were measured at two heights, 5 cm and 120 cm above the floor. The effect of the measurement heights on the concentration level was significant in the case of thoron. The monitoring of radon and thoron concentrations showed a lower radon concentration during work hours than at other times of the day. This can be attributed to the ventilation systems, including the air conditioner and natural ventilation, which normally operate during work hours. The diurnal variation was less observed in the case of thoron, as the change in its concentration during and after the working hours was insignificant. The study also investigated the influence of the floor level and flooring type on indoor radon and thoron concentrations. The elevated levels of radon and thoron were largely found in basements and ground floor levels and in rooms with concrete flooring.