PSI - Issue 22

António Curado et al. / Procedia Structural Integrity 22 (2019) 386–392 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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In what concerns radon gas exposure, this new Portuguese legislation defines a label called “reference level” of 300 Bq.m -3 for the mean annual threshold for radon concentration in homes, workplaces and buildings open to the public. When the indoor radon concentration surpasses the “tag” value of 300 Bq.m -3 , a set of mitigation procedures must be triggered off, according to Articles 145 to 150 of the Portuguese Law — Decreto-Lei n. o 108/2018 (2018). The Portuguese Law specifies a radon concentration level, the so- called “reference level” of 300 Bq.m -3 , to activate a set of remediation measures designed to decrease indoor radon concentration. This approach, taken in isolation, seems to be a highly simplified approach, since doesn't consider the occupancy period. In fact, when we are dealing with an office building, where the period of occupation is related to the working hours, the approach to estimate occupants´ radon risk must consider the exposure time as a very important variable. In fact, it's a completely distinct situation to have a group of workers exposed seven hours a day, in an office area, to radon level of 300 Bq.m -3 than having the same group of workers exposed to the same radon level in a pantry or utility area where they spend a maximum period of one hour a day. On the other hand, the regularity of occupation is as well rather different for both type of areas, being essential to highlight the difference between permanent occupation and episodic or sporadic occupation. Therefore, to avoid distorted conclusions, radon risk analysis must consider not only the indoor radon level but also variables such as the building type and its period of occupation, air renovation and the total number of occupants. 4. In situ monitoring 4.1. Experimental procedure The administrative building taken as case study makes part of a set of 15 public buildings chosen by the local municipality in a city in the northwest region of Portugal, for indoor radon assessment over the winter and summer 2018. Radon assessment was done using short-measurements, over periods of 1 week, both for winter and summer seasons. The radon sensors with 1-hour resolution were installed in a ground floor office room extensively occupied. In addition, in order to assess thermal comfort of the occupants, indoor air temperature and relative humidity measurements were collected. The office’ occupants were invited to fill a survey regarding ventilation, namely habits regarding opening and closing of windows during room occupation. The radon sensors were installed in places far away from the workstations, avoiding the proximity to radiation sources and electronic devices. Complementary, the sensors were kept away from fresh air intakes and air streams (windows and doors) in order to prevent abrupt air pressure drops. Radon sensors were provided by the Norwegian supplier Airthings and its calibration certificate was legally issued by the manufacturer. The technical specifications for the radon sensors are found in Airthings (2016). Graphs in Fig. 1 and Fig. 2 depict the variation over one week of the indoor radon concentration, air temperature and relative humidity during the monitoring period, using a line graph representation, for the instrumented room (ground-floor office). On the graphs are drawn 2 horizontal lines which represent the following:  Legal limit, according to the Portuguese law, for the indoor radon concentration (300 Bq.m -3 )  WHO limit recommended for all buildings (100 Bq.m -3 ) The air renovations operations undertaken by the room occupants´ (windows opening) are identified on the graphs, corresponding to the occupation periods. 4.2. Results summary