Radon Risk Classification
Indoor Radon Measurements
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
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.
RADON v.o.s., Novákových 6, 180 00 Praha 8 e-mail : firstname.lastname@example.org