Radon Risk Classification
The radon risk classification of foundation soils is based on the soil gas radon concentration measurements and on the
permeability of soils and rocks for gasses. This classification is obligatory in Czech Republic for each new building (detailed information about the method you can find here).
The purpose of radon survey is to classify the building site area from the point of view of the risk of radon penetrating
from the soil into the buildings. The radon risk classification is based on the assessment of the soil-gas radon (222Rn)
concentration and of the
permeability of soil and rock for gasses. Both parameters are evaluated
in the vertical profile up to the level of assumed building foundations
or to the level
of assumed contact building - soil.
The radon survey is based on soil-gas
radon concentration determination at each measured point of the area
investigated. Samples of soil-gas from the depth 0.8 m are collected by using a
small diameter hollow steel probe and a syringe (sampling
system). The extent of measurements is in full compliance with relevant
provisions - the detailed survey is performed in a 10 x 10 m grid in the area
of the assumed constructions, surveys for add-ons, reconstruction or on
reinforced surface are done at a corresponding number of sampling points of
this grid. When a building site of one family house is evaluated, it is
recommended to realise at least 15 soil-gas sample measurements. The values of
soil-gas radon concentration are measured in-situ (System
RM-2) or in the laboratory.
The radon risk classification is based on the assessment of values of soil-gas radon concentration and their distribution.
When categorising areas of individual buildings or groups of buildings (small statistical sets), particularly significant
statistical parameter for the evaluation of measurement results is the third quartile (i.e. the 75th
percentile). The values lower than 1 kBq.m-3 are not included in the data set evaluated by this method.
The permeability of foundation soils is based on the study of the specialised engineering geology reports and mapping
documents of the surveyed area, and on an in-site description (documentation of the vertical profile, a share of the "f"
fine fraction in the soil and disintegrated rocks in accordance with the Czech National Standard ČSN 73 1001
Foundation of Structures, Subsoil under Shallow Foundations), or on the direct in-site measurements of gas-permeability
(RADON-JOK) and its changes in vertical and horizontal directions.
The resulting output is the determination of the radon index of the
building site (RI). The final RI determination is derived from the
permeability data.
The radon potential of a building site - if the results of both soil
gas radon concentration measurements and in situ permeability
measurements are available for all measuring points, a radon potential
(RP) model can be used for determining the RI. To follow continuity
with the formerly used method the equation describing the RP parameter
is optimally defined as:
RP = ( CA - 1 ) / ( - log k - 10 ).
The third quartile of the soil gas radon concentration data set (CA75) and the third quartile of the permeability data set (k75)
are the input values for assessing a building site using the RP model.
The RP value enables the determination of RI as low, medium, or high
(if RP < 10, then RI is low; if 10 <= RP < 35, then RI is
medium; if 35 <= RP, then RI is high).
For numerical values of soil gas radon concentration and the expert
evaluation of soil permeability (given as low, medium, or high), the
assessment procedure is based on the classification table - see Tab 1.
The input parameter for RI assessment is again the third quartile CA75 of the soil gas radon concentration data set, or the highest CA75
calculated for the subsites comprising an inhomogeneous building site,
while the permeability is determined by expert evaluation.
The resulting radon index of the building site (RI) is given as one of the three categories: low, medium, or high.
Tab. 1: Radon index assessment
Radon
index (RI)
category |
Soil gas radon concentration
(kBq.m-3)
|
| low |
CA<30 |
CA<20 |
CA<10
|
| medium |
30<=CA<100 |
20<=CA<70 |
10<=CA<30
|
| high |
CA>=100 |
CA>=70 |
CA>=30
|
| |
low |
medium |
high
|
| |
permeability
|
It is apparent that buildings constructed outside of the areas with a
low radon risk must be protected against the radon penetration from
the ground. Hence the goal of legislative measures to prevent the
constructions of insufficiently protected buildings in locations with
an increased radon risk,
while maintaining the principle of optimisation. Due to the pattern of
radon distribution in the soil, and the frequent occurrence of local
non-homogeneity,
it is necessary to conduct a relatively high number of point
measurements of the soil-gas radon concentration in order to classify
the given location or area
into an appropriate category of radon risk.
The assessment complies with the legislative basis in Czech Republic -
the Czech Law No. 18/97 (on a peaceful utilisation of nuclear energy
and ionising radiation, so called "Atomic Law") with respect to changes
given by the Czech Law No. 13/2002, and the Decree of the State Office
for
Nuclear Safety No. 307/2002 on Radiation Protection.
If the area falls, from the point of view of the risk of radon penetrating from the ground into the building, into the low risk
category (low radon index), no preventive measures must be done.
If it falls into the medium risk category (medium radon index),
it is necessary to design the building´s structure in a way to minimise the radon penetration into the building.
The construction of the building requires basic protective measures.
If it falls into the high risk category (high radon index), it is necessary to design the building´s structure
in a way to minimise the radon penetration into the building. The construction of the building requires special protective measures.
The optimal protective measures can be chosen with respect to he Czech
National Standard CSN 73 0601 Protection of Buildings Against Radon
from the Soil.
Indoor Radon Measurements
RADON v.o.s. performs measurements of indoor radon concentration (OAR) using electret dosemeters and measurements of
gamma dose rate (D).
The evaluation of measurement results is
based on the criteria given by the Czech Law No. 18/97 ("Atomic Law") with
respect to changes given by the Czech Law No. 13/2002, and by the Decree of the
State Office for Nuclear Safety No. 307/2002 on Radiation Protection.
Electret dosemeters and exposure chambers
type RM-200 and RM-1000 (produced by the firm Nuklearni technika, Prague) are
used for indoor radon measurements. The system was verified by the State
Metrological Centre Kamenna. One measuring unit consists of two exposure chambers
with electret dosemeters.
The gamma dose rate is measured using the
radiometer DC-3E-98 (produced by ZMA Ostrov nad Ohri). The instrument was
verified by the Czech Metrological Institute Prague.
Evaluation criteria are given by § 6 of
the Law No. 18/97, with respect to changes given by the Czech Law No. 13/2002,
and by § 93 to § 97 of the Decree No. 307/2002. Reference values of exposure
to radon and to radon progeny indoors are defined as criteria that indicates the
need to decrease the exposure to radon and to other natural radionuclides. The
reference values are given by § 95. They enable to decide if the protection of
the building against radon penetration from soils, building materials and water
is sufficient, or if a remediation action is required to decrease the indoor
radon concentration.
The reference value for new buildings is
200 Bq.m-3 (Rn concentration in air) in living space.
The reference value for existing buildings
is 400 Bq.m-3 (Rn concentration in air) in living space.
The indoor radon concentration varies
during an annual climatic cycle and it depends on meteorological conditions and
other influencing factors. The short-term measurements of radon concentration (OAR)
are useful when the shortage of time does not allow to use the dosemeters with a
one-year exposure period. The short-term measurements enable to estimate annual
average values of OAR. The short-term measurements should be made under
conservative conditions, when higher indoor radon concentrations are expected (lower
ventilation, heating in operation, etc.).
The couples of electret dosemeters are placed into measured rooms for one week.
Other services
- Determination of effective dose at workplaces with a risk of higher exposure to naturally occurring radioactive materials (NORM)
- Environmental impact assessment, E.I.A.
- Quality assurance programme in X-ray dental diagnostics
- Accounting / book-keeping
- Equipment for radon risk monitoring
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