Abstract Good response was observed in simultaneously using six RAD7 detectors at high radon concentrations, temperatures and relative humidity conditions. RAD7 detectors were tested in laboratory using radon chambers from 13 up to 59.8 kBq m−3, statistical analysis allows to distinct between counting errors and radon variation. RAD7 detectors were exposure to extreme environmental conditions at uranium flat mine. High radon concentration in soil from a confined uranium mineral was 274.3 kBq m−3 at 44°C temperature and 20% relative humidity. Inside uranium mine radon increased from 1.0 up to 88.5 kBq m−3.