Impact of the human occupation on indoor radon concentration: a study based on in-situ measurements for a set of households in Alto-Minho

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BEHAVE 2016
4th European Conference on Behaviour and Energy Efficiency
Coimbra, 8-9 September 2016
IMPACT OF HUMAN OCCUPATION ON INDOOR RADON
CONCENTRATION: A STUDY BASED ON IN-SITU
MEASUREMENTS FOR A SET OF HOUSEHOLDS IN ALTO-MINHO,
PORTUGAL
António Curado1,2,*, Sérgio I. Lopes1,3
1: Instituto Politécnico de Viana do Castelo
Avenida do Atlântico, 4900-348 Viana do Castelo, Portugal
e-mails : {acurado,sil}@estg.ipvc.pt
web: http://www.ipvc.pt
2: CONSTRUCT-LFC
Faculty of Engineering (FEUP), University of Porto
Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal
web: http://www.fe.up.pt/~lfc-scc
3: Instituto de Telecomunicações
Campus Universitário de Santiago
3810-193 Aveiro, Portugal
web: http://www.it.pt
Keywords: Radon, Indoor Air Quality, Energy efficiency, Behaviour
Abstract
The Alto Minho region, in the northwest of Portugal, has one of the highest indoor radon
concentrations, due to the granitic nature of the soil. For long time granite has been one
of the most popular building materials, widely used in typical construction, not only in
Alto Minho region, but also in the North of Portugal, both in interior and exterior
applications. In Alto Minho typical countryside construction, the walls are generally built
with granite blocks, rough on all sides or finished on one or more sides, and the floors are
commonly made of solid granitic slabs. Besi des walls and floors, granite paving stones
are a popular way of paving a patio or a corridor, and the granite kitchen countertops are
also one of the most familiar uses for granite in the Alto Minho construction style.
The aim of this paper is to study the behaviour of a set of 9 granitic buildings located in
Alto Minho region, with a specific focus on the resident’s occupation and ventilation
conditions. The influence of variables such as the variation in occupancy and human
behaviour towards the operation of ventilation systems on the indoor radon concentration
is analyzed using statistic indicators.

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1. INTRODUCTION
Radon is a naturally occurring inert gas formed from the radioactive decay of elements of the
uranium series, which is found in small quantities in rocks and soil, as well as in building
construction materials [1]. The indoor radon level is influenced by the radium content in the
building foundation soil and its geo-morphological properties, soil permeability and building
ventilation systems (natural versus mechanical air exchange) [2] [3]. The gas is colourless,
odourless and tasteless with a half-life of 3.8 days [2] [4]. On decaying, emits radioactive
alpha particles that may cause lung cancer, if high concentrations are inhaled for a long time
[2] [3] [4]. Radon is the second most important risk factor for lung cancer after smoking [2]
[3] [5] [6] [7] [8]. It is estimated that the annual mortality from exposure to radon in
buildings represents 9% of all deaths from lung-cancer, and 2% of all cancer deaths, in
Europe [4].
The declaration of Radon as a human carcinogen by the International Agency for Research on
Cancer (IARC), led the United States Environmental Protection Agency (EPA) and the
European Commission (EC) to establish the so called action levels at 148 Bq.m-3 and 200
Bq.m-3, respectively [9] [10]. The UK Radiation Protection Division of the Health Protection
Agency, established an Action Level of 200 Bq.m-3 for domestic properties [11], the
International Commission on Radiation Protection (ICRP) have recommended an Action
Level in the range 200 to 600 Bq.m-3 [12], while in Luxemburg is 150 Bq.m-3, Ireland is 200
Bq.m-3 like in UK, while many other European countries use 400 Bq.m-3 for existing homes
and 200 Bq.m-3 for new houses [13] [14]. In Portugal, due to the granitic nature of the subsoil
and the tradition of using granite as a construction raw material for houses in countryside, the
centre and the north regions present high radon concentrations. For those regions, according
to the Portuguese Ordinance 353-A/2013 of 4 December, the legal limit is 400 Bq.m-3 [15].
The presence of radon in domestic houses, when the referred thresholds are exceeded,
determines the urgency of the implementation of radon mitigation solutions [9] [10].
The ventilation control is an important issue concerning radon mitigation [16] [17]. The lack
of ventilation of the houses has a strong potential to increase concentrations of pollutants
arising from sources inside or underneath the buildings, namely the radon [17] [16]. Radon is
a continuous source, which is therefore not responsive to the intermittent ventilation
techniques that can be used to deal with other indoor air pollutants [17] [16].
Requirements for indoor air quality (IAQ) in buildings are defined by existing ventilation
standards (e.g. EN15251) [18] [19]. Those standards define ventilation requirements to meet
comfort requirements of building´s occupants, but doesn´t reflect more serious health impacts
like asthma, allergies, chronic obstructive pulmonary disease, cardiovascular diseases, lung
cancer and acute toxication that are caused by exposures to pollutants that are present in
indoors [19]. There are no European guidelines to recommend how the buildings should be
ventilated to reduce the health risks of the occupants exposed to indoor air pollutants, like
radon for instance [19].
On the other hand, the reduction of the emission of greenhouse gases is the housing sector,
determined by improving buildings energy efficiency, imposes a tighter control of the

Curado. António and Lopes. Sérgio I.
3
ventilation schemes, leading therefore to a reduction of the ventilation rates [20] [19]. When
dealing with radon mitigation issues, the reduction of the ventilation rates can lead to public
health problems like the Sick Building Syndrome [20] [19].
The occupancy of the buildings as well as its ventilation schemes and schedules are quite
relevant on indoor radon air concentration. The main purpose of this study is to compare the
effect of ventilation on the indoor radon concentration of a sample of 9 granitic buildings
located in the Alto Minho region, Northwest of Portugal. Some of the instrumented buildings
were ventilated during a well-defined period of time along the experimental period, and some
other weren´t ventilated at all. The behaviour towards radon air concentration, indoor air
temperature and relative humidity, for both groups of buildings is quite different. Those
differences are analysed and discussed in this paper.
2. STATE OF THE ART
There have been some studies regarding the analysis of the indoor radon concentration
using in situ measurements. Some of those studies compared indoor radon concentration
with the limits specified in the applied regulations, before and after mitigation processes.
Some other studies highlight the importance of ventilation on indoor radon air
concentration, and other studied the effect of occupancy and lifestyle on radon
concentrations. There are, however, few studies focused on the variability on indoor radon
air concentration with the period of ventilation, with particular focus on residential
buildings. The main developed studies are the following:
 According to Groves-Kirkby, et al. [21], the analysis of pre-remediation and post-
remediation radon concentrations, measured in a set of 170 homes situated in high
radon areas in U.K., remediated using sub-slab depressurisation technology,
confirms that 100% of the homes remediated achieves reduction to values below
the U.K. Action Level of 200 Bq.m-3. The authors confirm that the total indoor
radon concentration within a dwelling can be represented by two components: the
ground radon, emanating from the subsoil entering the dwelling through its
foundations, as a component of the soil-gas and capable of being attenuated by
subslab depressurisation or radon-barrier remediation, and a second contribution
attributed to radon emanating from materials used in the construction of the
dwelling [21].
 Milner J., et al. [20], highlights the potential problems that may be caused by
energy efficiency measures that target heat losses from uncontrolled ventilation.
With regard to radon, the environmental exposure to this gas is altered by
increasing the air tightness of dwellings. Optimising ventilation strategies for
health is therefore more complex if all relevant exposures are taken into account,
and not only thermal or energetic issues.
 Madureira J., et al. [22], after measuring radon concentrations in 45 classrooms
from 13 public primary schools located in Porto, Portugal, observed that in 92.3

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and 7.7 % of the measurements, the limit of 100 and 400 Bq.m-3, established by
WHO IAQ guidelines and in the national legislation, respectively, was exceeded.
The study of the variation in radon concentration levels with the composition of
building floors confirmed the influence of soil as the main source of indoor radon.
 Martin Sánchez, et al. [23], carried out a survey to determine indoor radon
concentration in workplaces, evolving more than 200 measurements corresponding
to about 130 companies in Extremadura, Spain. The results show that 34% of the
monitored companies presented values that may need mitigation processes, and
16% of the instrumented workplaces presented levels above 400 Bq.m-3. The values
obtained in places with low ventilation rates like museums are particularly high,
due to their closed-in nature, usually needed to preserve artworks (paintings,
sculpture, jewellery, etc.).
 Barros-Dios, et al. [24], studied the factors that influenced on residential radon
concentration. After analyzing 983 homes in Galicia, Spain, concluded that 21.3%
of dwellings have a radon concentration above 148 Bq.m-3 and 12% have a
concentration above 200 Bq.m-3. The main factors that influence radon
concentration are: the age of the dwelling, the construction building material, and
the storey. The study shows that in high-rise buildings, radon levels are
appreciably less on the upper than on the lower storeys. Nevertheless, there are
other variables than those analyzed in the study fundamental for the analysis of the
residential radon concentration, like ventilation.
 Denman, et al. [17], analyzed the radon concentration data from a set of thirty-four
homes situated in Northamptonshire, UK, known to exhibit high radon levels. The
authors concluded that in single-storey and two-storey dwellings of conventional
construction, it is realistic to assume that the observed variability on radon
concentration in bedrooms and living rooms can be reliably attributed to
differences in the occupants' lifestyles, heating and ventilation. The investigation
showed that occupancy characteristics are important on indoor radon
concentration.
3. CASE STUDY
The selected case study is constituted by a set of 9 buildings located in Alto Minho region,
nearby the city of Viana do Castelo. The buildings have different periods of construction,
are mainly for residential purposes and were selected due to its granitic construction.
Despite some buildings are not residential, they were selected for in situ measurements
due its type of occupation or the adopted ventilation schedules. Table 1 shows the 9
samples considered for instrumentation, including the building type, the monitored
compartment and its occupation.
Figure 1 show the places in Alto Minho region where the 9 measured buildings are
located. By the analysis of the plan it is possible to observe a predominant spot of

Curado. António and Lopes. Sérgio I.
5
buildings located in the deep heart of the city of Viana do Castelo. There is however two
dots in Figure 1, representing samples D and E, respectively, located East and North from
Viana do Castelo.
Table 1: Considered samples for in situ instrumentation
Samples
Location
Building type/ Compartment
Occupation
A
Viana do Castelo
(Santa Maria Maior)
School Lab
In periods of one hour
by about 30 persons
B
Viana do Castelo
(Darque)
Residential Building
Bedroom
During night period
by 2 persons
C
Viana do Castelo
(Meadela)
Residential
Building Bedroom
Not occupied
D
Viana do Castelo
(Santa Marta de Portuzello)
Residential
Building Storeroom
Not occupied
E
Viana do Castelo
(Carreço)
Residential
Building Bedroom
Not occupied
F
Ponte de Lima
(Freixo)
Residential Building
Living Room
During evening period
by 2 persons
G
Viana do Castelo
(Meadela)
Residential Building
Bedroom
During night period
by 2 persons
H
Viana do Castelo
(Meadela)
Olive-Oil Mill
Not occupied
I
Viana do Castelo
(Santa Maria Maior)
Residential Building
Living Room
During evening period
by 2 persons
Figure 1: Alto-Minho region were the samples were collected.

Curado. António and Lopes. Sérgio I.
6
4. EXPERIMENTAL APPROACH
An experimental campaign that lasted the months of March and April 2016 was carried
out to assess indoor radon concentration in a set of 9 buildings in Alto Minho region,
Viana do Castelo, Portugal.
To evaluate radon air concentration, as well as indoor air temperature and relative
humidity, experimental measurements, with 1 hour resolution, were performed
continuously using digital radon monitors with incorporated data log to record the
collected data [25].
Since the measured rooms have similar granitic construction but different occupation and
ventilation schemes, it is possible to study the effect of the occupation and the ventilation
of each monitored room on the indoor radon concentration, relating it with the
measurements of the indoor air temperature and relative humidity.
The data logger devices used for experimental measurements process belong to Canary
Pro Series. The devices have a calibration certificate issued in March 9th 2016. The
specifications in detail of the devices used for data aquisition can be found in [25].
The buildings were monitored continuously for more than, at least, 48 hours for each
building. Additionally, manual registration of the ventilation periods was performed using
a specific paper form available in each room under monitoring. In that sense, users were
told to record – as accurate as possible – the periods of ventilation, by registering the time
period (start and end) of the ventilation actions.
5. RESULTS AND DISCUSSION
From the set of 9 granitic buildings evaluated, 5 were regularly occupied and ventilated
(samples C, D, E, F and H), and the remaining 4 had a residual occupation and were not
ventilated (samples A, B, G and I).
Figure 2 shows the evolution in time for the radon concentration and the thermo-
hygrometric measurements from sample C. In this example, the occupants performed three
ventilation actions, which are directly identified in the plot.
From the data in Figure 2, it is possible to observe a reduction of the radon concentration
as a result of the ventilation actions. Moreover, it is also possible to observe the cyclic and
inverse evolution of the thermo-hygrometric measurements. The cyclic behaviour is
directly related with the outdoor environmental changes, i.e. changes between day and
night, for the period under evaluation. Other important observation is related to the
increase of the radon concentration during the night, where the temperature tends to
decrease, and in opposition, relative humidity tends to increase.
Other example of the evolution in time for the radon concentration and the thermo-
hygrometric measurements can be observed in Figure 3. In this case data corresponds to
sample E, and two ventilation actions, directly identified in the plot, were performed.

Curado. António and Lopes. Sérgio I.
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Figure 2: Radon concentration and thermo-hygrometric measurements for sample C.
Figure 3: Radon concentration and thermo-hygrometric measurements for sample E.
From the data presented in Figure 3, it is also possible to observe a considerable reduction
of the radon concentration as a result of the two ventilation actions. Temperature and
relative humidity also present an inverse evolution with an abrupt decrease in second

Curado. António and Lopes. Sérgio I.
8
ventilation action, which can be justified by a considerable difference to the outdoor
environmental conditions in the time interval that the ventilation action was performed.
Figure 4 shows the overall statistical results of the thermo-hygrometric measurements
using a boxplot representation. In this type of plot the space between the different parts of
the box (quartiles) indicates the degree of dispersion of data with relation to the median,
being the outliers plotted as individual points.
Figure 4: Overall thermo-hygrometric statistical results.
Data in Figure 4, is in line with the information of the ventilation processes identified
when the experiments were designed. For example, sample A represents data from a room
with a fan exhaust vent performing continuous active ventilation. All the other residence
buildings that were monitored did not have any type of active ventilation system acting.
Excluding sample A, the median indoor temperature for the residential buildings under
monitoring was in the interval between 11ºC and 19ºC, which is normal for the region in
the spring season, and the relative humidity was found to present median values in the
interval between 70% and 90%, which was expected given the proximity to the sea.
Using the same type of data representation, Figure 5 illustrates the overall statistical
results for the radon concentration for all the buildings under monitoring. These results
show that 67% of the evaluated buildings have radon concentrations below the maximum

Curado. António and Lopes. Sérgio I.
9
value of 400 Bq.m−3 suggested by Portuguese regulation, and clearly exceeding the EPA
action level of 400 Bq.m−3, being in these cases the human occupancy – mostly through
passive ventilation processes – working as a radon concentration mitigation factor.
Three samples, E, F and G, exceeded the Portuguese regulation limits with median values
of approximately 1300, 1150 and 600 Bq.m−3, respectively. The obtained results are in
line with what it was expected – the three monitored rooms weren´t ventilated during any
period of time -. Room E is not occupied at all. On the other, despite being occupied, the
occupants of rooms F and G don´t have ventilation routines. Besides that, the three rooms
have granitic walls and floors, some of them not covered with plaster and complet ely
exposed to the indoor environment.
Figure 5: Overall radon concentration statistical results.
6. CONCLUSIONS
A lot of the residential buildings in Alto Minho have a comprehensive need of retrofitting
as a result of insufficient maintenance and natural decay due to their predicted end of
service life. Due to the strong predominance of granitic construction, one of the main
concerns when designing a retrofitting solution to increase the Indoor Air Quality (IAQ)
of the occupants is to reduce the risk of high radon concentrations.
The distribution of indoor radon levels has been found to be largely dependent on building
occupation and ventilation. The highest value of the radon concentration found exceeded
2000 Bq.m−3.
For the samples that exceeded the Portuguese regulation limits, some recommendations
can be undertaken, namely the following:
i. To strongly encourage householders to take steps to remediate the situation;
ii. In existing buildings, the methods adopted to reduce indoor radon
concentrations should rely on two solutions: dilution and/or pressure change,
achieved by the installation of a pressure-modifying sump, generally in
conjunction with an extraction fan [16] [17];

Curado. António and Lopes. Sérgio I.
10
iii. If possible, to install a natural under-floor ventilation, in the case of suspended
flooring, or by construction of a passive sump below the level of the ground-
floor [16] [17];
iv. The approach for new-build houses is the installation of a radon-proof
membrane across the entire ground level of the house [16] [17];
v. Both for existing or new buildings ventilation is the key for mitigation of the
radon high concentrations;
These recommendations are in line with the strategy followed in Europe and United
States, broadly described in the State of the Art, cf. Section 2.
As a major drawback, it was identified that, by increasing ventilation, the thermal and
hygrometric performance of the building varies, and thus, impacting on the energy
efficiency of the building.
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