Determination of the indoor radon concentration in schools of Tenerife (Canary Islands): a comparative study.

A radon survey was carried out in 18 high schools located in Tenerife Island when anti-pandemic strategies were used to reduce COVID-19 dissemination during 2021. High schools were located in radon-prone areas previously identified by the Spanish Nuclear Safety Council. Our results showed that 12 high schools presented radon activities lower than 100 Bq/m, 5 high schools presented values in the range 100-200 Bq/m, and only 1 high school presented radon activity concentration higher than 200 Bq/m. Such values are below the reference level (300 Bq/m) recommended by the Spanish legislation in the Basics Document of Health Standards (section HS6) of the Technical Building Code and the European Union directive (2013/59/EURATOM). Assuming an indoor occupancy time of about 1620 h per year, the annual dose contribution due to indoor radon exposure ranged from 0.07 to 1.18 mSv/year. Comparing such result against previous values reported in the literature on the island of Tenerife, we conclude that during the pandemic situation the indoor radon concentration (median valued) was reduced from 130.9 (2007) to 73.5 (2021) Bq/m. Finally, continuous indoor radon concentration measurements were obtained to study short-time fluctuations (intra-day changes) under different ventilation conditions.