Radon mitigation in workplaces
Radon mitigation in workplaces
The radon mitigation methods used in low-rise residential buildings and apartment buildings are also applicable to workplaces and larger buildings. The most significant differences are the large floor area of the buildings and the ventilation systems used. During working hours at workplaces and in public buildings, the air exchange rate is normally set much higher than in dwellings. The ground-level floor structures of large buildings are often composed of separate slabs, with seams that increase leaks of radon-containing air.
Due to timed and automatic exchange of incoming and exhaust air, the radon concentration at workplaces tends to be significantly lower during working hours than in the evening or at night. This is further affected by the level of air exchange and any separate exhaust fans in places such as toilets and staircases. In buildings that are only equipped with an extract ventilation system, the changes in negative pressure and ventilation between day and night may sometimes cause the air to have a higher radon concentration during daytime. Strong local ventilation and fume cupboards may also result in negative pressure, and consequently may also affect the radon concentration.
If the building has a timed ventilation system, it is advisable to measure the radon concentration during working hours to find out the variation between night and day before carrying out the actual radon mitigation.
Figure 1 depicts a significant variation between day and night time radon concentrations at a workplace with an automatic incoming and exhaust air exchange. The radon concentration measured in the box measurement of the first two months was 530 becquerels in one cubic metre (Bq/m3). After this, the radon concentration during working hours was measured for one week. The radon concentration during working hours was 80 Bq/m3 and the average radon concentration for the whole week was 480 Bq/m3. The highest radon concentration measured was 870 Bq/m3.
Radon mitigation in the workplace can sometimes be done simply by adjusting and improving the existing ventilation system. Setting the working-hour ventilation to start earlier has often given good results. In most premises, increasing ventilation three hours before the start of the workday has proven effective. Enhancing ventilation at the right time ensures that the radon concentration is low already when employees arrive at work in the morning. In more problematic situations, the radon concentration was still some thousands of becquerels per cubic metre (Bq/m3) during the first working hours, which means the radon concentration during working hours exceeded the action level.
At another workplace, the average radon concentration over a two-month measurement period was over 1,000 Bq/m3. The working-hour ventilation at the workplace was set to start earlier, at 05:00. A control measurement was carried out using a radon monitor. The measurement indicated that at 07:00, radon concentration was at around 400 Bq/m3, and the concentration during working hours, i.e. 08:00–16:00, was 100 Bq/m3. The average for the whole week was approximately 1,000 Bq/m3 with a fluctuation range of 40–2,710 Bq/m3. If the ventilation had not been set to start earlier, the average radon concentration during working hours would have exceeded the level of 400 Bq/m3.
If radon concentration during working hours exceeds the action level despite proper ventilation, other radon mitigation methods, such as sub-slab suction, radon wells, or sealing the structures, may be effective.
When using sub-slab suction at workplaces, the typical method is to set up several suction points that can be connected to one or more exhaust fans. The structure of the suction points are similar to those in low-rise residential buildings, but the number and location of the points must be planned case by case. More suction points can be added later if necessary. In some cases, it can be useful to measure the vacuum under the floor at different parts of the building.
Radon wells have been successfully used for radon mitigation in large buildings built on gravel. Several radon wells with a power range typically ranging from 150 to 350 W have been installed around the large buildings. The measured radon concentrations have been several thousands of becquerels per cubic metre. Similarly to low-rise residential buildings, the best place for a radon well is in the middle of the long wall of the building, and on the upper side if the building is built on the slope of a hill.
Sealing the structures of the building has been an effective method for tackling radon problems in industrial buildings. For example, the floor slabs of large halls may consist of several different slabs with unsealed seams. Seams between floors and pillars that penetrate the floors, as well as the covers of the covered drain inspection wells, must be carefully sealed. Sealing these is made easier by the open floor seams typical to large buildings, as they can be sealed without taking apart any structures.