RADON CONCENTRATIONS AFFECTED BY DIFFERENT FACTORS IN TWO OFFICE BUILDINGS. Raimo Halonen, Pirjo Korhonen, Pentti Kalliokoski and Helmi Kokotti

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1 Radon in the Living Environment, 25 RADON CONCENTRATIONS AFFECTED BY DIFFERENT FACTORS IN TWO OFFICE BUILDINGS Raimo Halonen, Pirjo Korhonen, Pentti Kalliokoski and Helmi Kokotti Department of Environmental Sciences, University of Kuopio P.O.Box 1627, 7211 Kuopio, Finland In the study, the factors affecting concentrations of radon vertically lines were surveyed in two large office buildings. Integrated concentrations of radon were determined with alpha track etch films (2 months) and continuous monitoring (2-6 days) was carried out with Pylon AB-5 equipment. The effective air exchange rates were analysed by the tracer gas method with an infrared analyser and rates of air flows from vents were measured with a thermoanemometer. Pressure differences were measured with a manometer and temperature differences with thermoelements. Measurements were conducted during springtime Continuously measured levels of radon varied from 17 to 129 Bq m-3. The variation of integrated radon levels including nights and weekends was larger ranging from 2 to 35 Bq m-3. The Finnish limit value of 4 Bq m-3 was not exceeded in any room. Correlation between continuously measured and integrated concentrations of radon was quite high (R2=.8125). Concentration of radon was observed to increase if depressurisation of the room increased, the effect was seen even on the third floor. Expectedly, radon levels were the highest in piping tunnels nearest the soil. However, there were not essential changes in radon levels between different floors. Radon levels correlated with air exchange rate quite good in building A (R2=.489) and only slightly in building B (R2=.542). Theoretical concentrations of radon due to stone building material were generally less than 5 % of measured concentrations. Key words: radon, pressure difference, ventilation, exhalation, concrete INTRODUCTION Radon sources and indoor concentrations in Finland The most important source for indoor radon is soil, and radon enters the buildings through cracks. Depressurisation and ventilation system affect crack flows. The exhalation rates of radon are found to vary between 2 and 32 Bq m -2 h -1 in concrete slab with thickness of,2m (Mustonen 1984). The average of concentration of radon in Finnish dwellings is high, 123 Bq m -3. About half a million (12.3%) Finnish people are exposed to levels exceedings 2 Bq m -3 radon levels in their dwellings. Concentrations of indoor radon is, however, markedly different in different provinces. The highest radon concentrations in Finland are found in Southern-Finland. High levels can also be found elsewhere in Finland, especially in buildings located on the eskers (Arvela 1994). The Finnish Center for Radiation and Nuclear Safety (STUK) started surveying radon levels on the other workplaces than mines at Studies of STUK have hitherto been conducted in 35 workplaces at communes belonging to areas, where over 25% of measured annual average radon levels have exceeded 4 Bq m -3 in dwellings. Radon levels have exceeded 4 Bq m -3 in about 1 % of the 45 urban workplaces. The workplaces studied were mainly located on the ground level (Annanmäki et al., 1996). Korhonen (1997) have found that violation of limit value of 4 Bq m

2 25 Radon in the Living Environment, were somewhat more common in underground workrooms, 17 % of all places. Therefore, it was now investigated how radon concentration varies vertically in multistore buildings. MATERIALS The study buildings Radon concentrations, air exchange rates and pressure differences were measured continuously during several days (from two to six) in rooms of two large multi-floor office buildings. These were located in central Finland where low concentrations of radon are generally found. Measurements were conducted at twelve points of three vertical lines in building A (12 m 3 ) and at six points in two vertical lines in building B (11 m 3 ). The total number of employees in these buildings was approximately 75. The outer walls were made of concrete, insulation layer and brick (the outer surface). The floors and ceilings were constructed from concrete elements. The buildings were constructed on a concrete slab. Around the buildings under the slab located pipe tunnels. Floors and upper floors were cavity slabs (h=.2 m). Frameworks were in-situ concrete walls (h=.2 m) and - columns. Partition wallings were made from brick or from fibreboard and wood. The room volumes varied between 2-15 m 3. Both buildings were equipped with mechanical supply and exhaust ventilation system. The office rooms and rest rooms were equipped with mechanical exhaust vents and supply air was transferred from corridor. Laboratories and classrooms were equipped with mechanical exhaust and supply vents. Ventilation was adjusted to operate in full capacity during working hours (7.-17.) in office rooms and rest rooms. The ventilation of laboratories and classrooms could manually be increased to full capacity when needed. Measurement technique The integrated long-term levels of radon were determined by alpha track etch films (3 films in building A and 2 films in building B) and analysed by STUK. Continuous radon levels were measured with Pylon AB-5 equipment by using Lucas cell method in 18 rooms (12 rooms in building A and 6 rooms in building B). Room volumes, operation of ventilation, constructional knowledge and working time and number of the employees were asked and observed. Pylon AB-5 equipment includes a detector, which was connected to a photomultiplier and a system of data collection based on a microprocessor. The output data of the Pylon detector were processed with SP-55 software run on a PC. Continuous measurements were measured during periods ranging from two days to six days. Alpha films were in the rooms for two months. The pressure differences between outdoor and indoor were monitored by an electronic manometer together with a datalogger. Temperature differences between outdoor and indoor air were measured with thermoelements together with the datalogger. The output data of the manometer and the thermoelement were processed with DecipherPlus- software run on a PC. Temporary air exchange rates (k, h -1 ) in 18 rooms were measured by the tracer gas technique and the dilution method using nitrogendioxylene as the tracer gas and an infrared spectrophotometer (Miran 1A) as the analyser. Exhaust air flows were measured also with a thermoanemometer on exhaust air vents in the same rooms. Measured and planned air exchange rates were compared. 194

3 Radon in the Living Environment, 25 RESULTS Concentrations of radon During several days continuously measured concentrations of radon varied from 17 to 129 Bq m -3 and radon concentrations during working hours varied from 17 to 13 Bq m -3. Average concentrations of two months were higher being in the range of 2-35 Bq m -3. However, the limit value of working hours, 4 Bq m -3, did not exceed in any work room (figures 2 and 3). The correlation between continuously and integrated measured radon concentrations were quite good (R 2 =.8) (figure 4). The highest concentrations of radon were found in the piping tunnels, where no mechanical ventilation existed and they located partly under the soil level. Walls and floors in piping tunnels were no-coated concrete. Location of sampling spaces are former presented in figure 1. Marks in figures 2,3 and 6 and in tables 1 and 2. For example. A 1 1 Effect of ventilation on radon levels building measuring point floor Air exchange rates in the rooms (n=18) varied from.3 to 7.7 times per hour. Concentrations of radon measured during working hours (8-16) seemed to increase when air exchange rate decreased (R 2 =.5) in building A but only slight effect of air exchange rate on radon concentration was found in building B (figure 5). The air exchange rates measured by the tracer gas technique were generally almost the same than planned air exchange rates (figures 6 and 7). The greatest differences between planned and measured air exchange rates were caused by changing the purpose of rooms or short circuit ventilation. In measuring points A13, A32 and A42 there were no planned air exchange rates available. Effect of pressure and temperature differences on radon levels Radon concentrations increased in the part of the measured rooms when depressurisation increased (figure 8). However, the correlation between radon concentration and indoor outdoor pressure difference in the whole building was low being negative in the building A (R=.27) and even positive in the building B (B=.66) (figure 1). On the other hand, when the temperature difference was observed to increase also the negative pressure increased, which in turn increased indoor concentration of radon (figures 8,9 and 11). Effect of depth on radon levels In both buildings piping tunnels and heating rooms, where existed no-coated concrete surfaces, are processed together. Radon concentrations in piping tunnels and heating rooms were the highest. However, there were not essential differences on radon concentrations between different upper floors ( figures 12 and 13 ). 195

4 25 Radon in the Living Environment, Effect of coated stone material on radon levels Walls, which included stone material, were either painted brick or painted concrete. Concrete ceilings were painted. Floors were coated either with plastic rug or linoleum plate. Indoor radon concentration caused by radon exhalation from stone material is calculated by following equation C Rnm =EF / hv, where C Rnm = Concentration of radon (Bq m -3 ) caused by construction materials, which included stone material E = radon exhalation rate (Bq m -2 h -1 ) (Mustonen 1983) h = air exchange rate (h -1 ) (table 1) V = rooms volume (m 3 ) (table 1) F = area of stone material (m 2 ) (table 1) Theoretical radon concentrations due to stone material were generally less than 5 % of measured low means of radon concentrations in the most rooms. Thus, the most of radon concentration originated from soil even in upper floors. However, the range of percentage parts was quite wide, from 8 % to 29 %. The overestimation of material exhalation in three rooms could be due to different coating materials and variation of real air exchange rate. CONCLUSIONS Concentrations of radon were low and did not exceed the Finnish limit value, 4 Bq/m 3, in any place. Highest levels were measured in piping tunnels, where existed no ventilation and construction material was no-coated concrete. Radon levels were observed to increase in some rooms when depressurisation increased even on the third floor. Concentration of radon caused by exhalation of construction material was generally less than a half from measured concentrations. Thus, the soil beneath the buildings was the main source for radon even in upper floors. ACKNOWLEDGEMENTS The study was supported by the University of Kuopio. REFERENCES [1] Annanmäki M., Oksanen E. and Markkanen M. Radon at workplaces other than mines and underground excavations. Environmental International 1996:22, suppl1:pp [2] Arvela H. Costs of radon mitigation in Finnish dwellings. Finnish Centre for Radiation and Nuclear Safety (STUK). 1994:STUK-A114 (In Finnish, abstract in English) [3] Korhonen Pirjo. Survey and mitigation of occupational radon exposure in underground workplaces. Licentiate thesis. University of Kuopio, Department of Environmental Sciences [4] Mustonen Raimo. Natural radioactivity in and radon exhalation from finnish building materials Health Physics Vol. 46, No 6 (June) pp ,

5 Radon in the Living Environment, 25 Table 1: Air exchange rate, area of stone material and volume of the measured rooms. Location of measuring points are presented in figure 1. Measuring point Air exchange rate (h -1 ) Stone material area (m 2 ) Volume (m 3 ) A A A A A A A A A A Mean B B B B B Mean

6 25 Radon in the Living Environment, Table 2: Continuously and integrated measured concentration of radon. Calculated radon concentration and percentage parts of calculated radon concentration from radon concentrations of measured continuously and integrated. Concentration of radon Measured Measuring point Continuous (Bq/m 3 ) C Rn Alphafilm A B / (Bq/m 3 ) Concentration of radon Calculated Calculated E min = 2Bq/m 2 h (Bq/m 3 ) C Rnm Calculated E max = 32Bq/m 2 h (Bq/m 3 ) Continuous E min E / max R Rn R Rn (% / %) C Rnm / C Rn % Integrated E min E / max R Rn R Rn (% / %) A / 45 4 / 65 A / 41 2 / 35 A / 35 2 / 35 A / / 2 A / / 154 A / / 27 A / / 43 A / 94 6 / 1 A / 17 1 / 18 A / 34 2 / 35 Mean / / 53 B / / / 25 B / / / 7 B / / / 16 B / / / 29 B / / 24 8 / 13 Mean / / 96 7 /

7 Radon in the Living Environment, 25 Figure 1: Sampling spaces in the building A (left) and B (right). 16 Concentration of radon (Bq m -3 ) continuously Integrated A11 A12 A13 A14 A21 A22 A31 A32 A33 A41 A42 A43 Rooms Figure 2: The integrated (alpha films) and continuously (Pylon AB-5) measured concentrations of radon in different rooms of the building A. 199

8 25 Radon in the Living Environment, 16 Concentration of radon (Bq m -3 ) B21 B22 B23 B24 B11 B12 Continuously Integrated Rooms Figure 3: The integrated (alpha films) and continuously (Pylon AB-5) measured concentrations of radon in different rooms of the building B. 14 C oncentration of continuously measure ra don (B q m -3 ) y =.6532x R 2 = C oncentration of integrated measured radon (B q m -3 ) Figure 4: Correlation between continuously and integrated measured concentrations (n=18) of radon in both of the buildings. 2

9 Radon in the Living Environment, 25 Concentration of radon (Bq m -3 ) Building A Building B y = -5,7239x + 45,372y = -,1627x + 22,156 R 2 =,489 R 2 =, Measured air exchange rate (h -1 ) A whole time A working time B whole time B working time Lin. (A working time) Lin. (B working time) Figure 5: Concentration of radon versus air exchange rate in buildings A and B. 8 Air exchange rate (h -1 ) planned measured A12 A13 A14 A21 A22 A32 A33 Rooms A41 A42 A43 A51 A52 A53 Figure 6: Planned and measured air exchange rates in the building A. 21

10 25 Radon in the Living Environment, 9 Air exchange rate (h -1 ) planned measured B11 B12 B22 B23 B24 Rooms Figure 7: Planned and measured air exchange rates in the building B Concentration of radon (Bq m -3 ) : : 12: : 12: : 12: : Pressure difference (Pa) Temperature difference ( o C) Time (h) Figure 8: Concentration of radon, pressure and temperature differences between indoor and outdoor air during four days in the office room on the third floor of the building A. 22

11 Radon in the Living Environment, 25 7 Concentration of radon (Bq m -3 ) y = x R 2 2 = Pressure difference (Pa) Figure 9: Concentration of radon versus indoor-outdoor pressure difference in the office room on the third floor of the building A. 7 Concentration of radon (Bq m -3 ) y = x R 2 = Pressure difference (Pa) Figure 1:The averages of continuously measured radon concentration versus indoor-outdoor pressure difference in the building A (n=9) and in the building B (n=4). Separately calculated correlations were.27 (negative) in A and.66 (positive) in B. 23

12 25 Radon in the Living Environment, 35 Temperature difference ( o C) y =.9494x R 2 = Pressure difference (Pa) Figure 11:Temperature difference versus pressure difference (n=13) in building A and B. 25 n=5 Building A Concentration of radon (Bq m -3 ) n=4 n=11 n=7 n=3 piping tunnel ground floor 1st floor 2nd floor 3rd floor Floor Figure 12:Average of integrated concentrations of radon on different floors of building A. 24

13 Radon in the Living Environment, 25 Concentration of radon (Bq m -3 ) Building B n=2 n=4 n=6 n=5 n=3 piping tunnel ground floor 1st floor 2nd floor 3rd floor Floor Figure 13:Average of integrated concentrations of radon on different floors of building B. Building A, integrated measurement (n=1) Concentration of radon (Bq m -3 ), calculated Bq/m 2 h y =,89x - 15,7 R 2 =, Bq/m 2 h y = 1,44x - 25,2 R 2 =, Concentration of radon (Bq m -3 ), measured rate 32 rate 2 rate 32 rate 2 Figure 14:Comparison between calculated and integrated measured concentration of radon in building A. 25

14 25 Radon in the Living Environment, Building A, continuous measurement (n=1) Concentration of radon (Bq m -3 ), calculated Bq/m 2 h 32 Bq/m 2 h y =,7841x - 14,796 y = 1,2519x - 23,189 6 R 2 =,5366 R 2 =, rate 32 rate 2 rate 32 rate 2 Concentration of radon (Bq m -3 ), measured Figure 15:Comparison between calculated and continuously measured concentration of radon in building A. Concentration of radon (Bq m -3 ), calculated Building B, integrated measurement (n=5) 32 Bq/m 2 h y = -1,1125x + 49,5 R 2 =, Bq/m 2 h y = -,7x + 31 R 2 =, Concentration of radon (Bq m -3 ), measured rate 32 rate 2 Lin. (Exhalatio n rate 32 ) rate 2 Figure 16:Comparison between calculated and integrated measured concentration of radon in building B. 26

15 Radon in the Living Environment, 25 Building B, continuous measurement (n=5) Concentration of radon (Bq m -3 ), calculated Bq/m 2 h y = 6,2222x - 127,67 R 2 =, Bq/m 2 h y = 9,8889x - 22,67 R 2 =, Concentration of radon (Bq m -3 ), measured rate 32 rate 2 rate 32 rate 2 Figure 17:Comparison between calculated and continuously measured concentration of radon in building B. 27

16 25 Radon in the Living Environment, 28