Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

EXPERIENCES IN PROTECTION AND REMEDIATION
Martin Neznal, Matej Neznal
RADON v.o.s.Novakovych 6, 180 00 Praha 8, Czech Republic

Abstract
The paper presents an overview of some parts of the Czech Radon Programme - results and
experiences resulting from the work of many experts from different institutions (Czech
Geological Survey; Charles University of Prague, Faculty of Science; State Office for Nuclear
Safety; National Radiation Protection Institute; Czech Technical University, Faculty of Civil
Engineering; National Institute for Nuclear, Chemical and Biological Protection; Radon v.o.s.
and others). During the last 15 - 20 years. Four main topics are discussed: (i) radon
protection of new houses based on an individual approach - a building site characterization;
(ii) preventive measures in new houses; (iii) remedial measures in existing buildings; (iv)
human factor that may become a weak point of the system in some cases.

Introduction
The first reference to negative health effects of radon appeared in the 16th century: Paracelsus
described a specific “miners disease” that occurred in silver mines in Jachymov
(Joachimstahl) and Schneeberg, two towns located near the border between Czech Republic
and Germany. The symptoms and the development of the disease differed from those of
tuberculosis. But as late as in 1951, W.F. Bale (USA) discovered the reason: inhalation of
short-term radon decay products (Bale, 1951). The discovery was followed by first
epidemiological studies, in the Czech Republic organized by J. Sevc at al. (Sevc, 1993). In
1956, H. Hultquist observed high indoor radon concentrations in Sweden (Hultquist, 1956).
Other papers (Akerblom, 1984) described radon from bedrock as a main source of daughter
products in dwellings. In the 80s, high indoor radon concentrations were also observed in
Czech houses, at first in houses built from materials with higher content of 226Ra (slag
concrete; so-called START houses).
The first governmental resolution about radon, as well as the first proposal of the uniform
method for radon risk classification of foundation soils appeared in 1990 (Barnet, 1990). The
governmental resolution represents the starting point of the Czech Radon Programme.

Radon Protection of New Houses in the Czech Republic - Individual
Approach
In European countries, a decision making in the pre-construction phase is typically based on
radon risk mapping, or on modelling. However, since 1991 in the Czech Republic, the radon
potential for prospective building sites has been characterizing by performing in-situ
measurements in the soil. Based on these measurements, protective measures are then
included in the dwelling design.
The main advantage of the method is given by the fact that it is a site-specific, individual
approach. It should enable to propose an optimal preventive strategy corresponding to local

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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

conditions. Disadvantages - connected for example with temporal changes of measured
parameters - are not critical. In our experience, spatial variations of measured parameters are
more important than temporal ones. The soil-gas radon concentrations, as well as soil
permeability may vary, often greatly, over a small distance. The occurrence of heterogenities
may indicate the presence of faults or tectonic zones or possible kasrst geological formations.
Because homogeneous geological structure are rare, any evaluation based on a single
measurement would be extermly limited. On the other hand, the occurrence of spatial
variations represents a good reason for the protection of a building based on the results of a
building site characterization, not on large scale radon risk maps. (Neznal, 1991, Neznal,
1992, Neznal, 1996a, Neznal, 1996b, Neznal, 1996c, Neznal, 1997, Neznal, 2004b).
In accordance with the Czech Atomic Law, results of the building site characterization are
used for the design of protective measures. If the radon index is other than low (i.e. medium,
or high), the building must be protected against radon. Protective measures are designed and
installed in accordance with the Czech National Standard (CSN 730601 Protection of houses
against radon from the soil; 1995, 2000, 2006).
The standard method for the determination of the radon index of prospective building sites
has been modified (Barnet, 1994, Neznal, 2004a), but the basic principles have remained the
same. The evaluation is based on measurement of soil-gas radon concentration and on in situ
measurement, or on expert evaluation of soil permeability. Simple, low-cost sampling and
measuring techniques are used. A description of the system for soil-gas sample collection
follows as an example (See Fig. 1).
The sampling system consists of a small-diameter hollow steel probe with a free, sharpened
lower tip. The probe is pounded into the ground to a desired depth below the ground surface
using a hammer. A punch wire is then inserted into the probe and the tip is moved a few
centimeters lower using a hammer again. This action creates a cavity at the lower end of the
probe. A cap containing a rubber stopper and a needle is placed on the open upper end of the
probe. The soil-gas is sucked and samples of a controlled volume are collected using a largevolume syringe. To obtain the proper vacuum and to avoid underestimating the soil, gas
concenctration, the entire system must be perfectly sealed. More detailed information on
sampling and measuring techniques has been published (Barnet, 2008).

(a)

(b)

(c)

Fig. 1. Soil-gas sampling: (a) Inserting the sharpened tip into the lower end of the probe. (b) The sharp tip is
moved a few centimetres lower - this action creates a cavity at the lower end of the probe. (c) Soil-gas sample
collection using a syringe.

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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

Currently, apporximately 100 organizations (mostly private firms) are providing radon index
services for prospective building sites. Each technician performing these services has to pass
a training course and perform a comparison measurement of soil-gas radon concentration at
field radon reference sites (Matolin, 1991, Matolin, 2002). A regular metrological
verification of all measurement devices for the determination of soil-gas radon concentration
is also required. Only firms that fulfil all above mentioned requirements are authorised by the
State Office for Nuclear Safety to perform measurement in this field.

Preventive Measures in New Houses - Technical Solutions and Experiences
The Czech National Standard CSN 730601 concerns not only preventive measures in new
houses, but also remediation of existing buildings. It also contains principles of designing and
application of various types of radon reduction techniques, as well as requirements for radonproof insulation (Jiranek, 2000, Jiranek, 2001).
Protection of new houses against radon penetration from the ground is based on the use of
radon-proof insulation; or in combination with passive, and/or active ventilation systems. The
basic principles can be summarized as follows: 1. Only materials with known radon diffusion
coefficients can be used. 2. Special attention must be given to jointing and to pipe
penetration. 3. The passive ventilation systems must be installed in such a way that they can
be easily converted to forced (active) systems. Simple airing of the drainage layer by means
of pipes that run from one side of the building to another is not an acceptable solution. The
prefered ventilation system consists of several perforated pipes that are connected to one
vertical exhaust pipe on which a fan can be installed in the future.
Realization of preventive measures against radon started in the Czech Republic more than 15
years ago. Long-term measurements of indoor radon concentration have shown that the
protection has failed in a non-negligible number of houses (Jiranek, 2006) with greater
failures occuring in homes built before 1995 (ie. before publication of the first version of CSN
730601). The most important factors responsible for failures are:
- leakages in joints and around pipe penetration,
- partial application - insulation is not applied over the entire surface,
- perforation of insulation during construction works,
- use of insulating materials that were not tested on radon diffusion, or use of low quality
products, and
- passive ventilation with inlet and outlet holes in external walls only (without vertical
exhaust).

Remedial Measures in Existing Buildings - Technical Solutions and
Experiences
Different types of remedial measures in older buildings had been tested in the past (i.ie.
ventilation of indoor air with heat recovery, radon-proof membranes, protective coating of the
floors, etc.) However, more recently, sub-slab ventilation has shown to be the most effective
and appropriate system to solve problems with radon in existing houses (Jiranek, 1998,
Jiranek 2002, Jiranek 2004). Soil ventilation systems used in the Czech Republic are usually
formed by:
- one, or several perforated tubes drilled beneath existing floors (from the cellar, from an
external chase, or from an internal chase),
- one, or several radon sumps installed into the sub-floor region of the building,
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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

- a network of flexible perforated pipes inserted into the drainage layer of coarse gravel placed
beneath the floors (reconstruction of floors is necessary in this case),
- a combination of the above stated measures.
The principles of designing and application of various ventilation systems are published in the
Czech National Standard CSN 730601. Becasue of its versatility, sub-slab ventilation can be
successfully applied in nearly all types of houses. An example concerning a family house
with extremely high indoor radon concentrations is described below.
The house is located in Northern part of the Czech Republic, in region of former silver
mining. It has a small cellar located under 1/5 of the ground floor area. Two types of floors,
i.e. a timber floor and a cracked concrete slab have been found in the ground floor. Very high
average indoor radon concentrations (about 20000 Bq.m-3 in some habitable rooms; about
70000 Bq.m-3 in the cellar) were observed in the house during detailed diagnostic
measurements performed in 2004 (See Fig. 2):. The indoor radon concentration in the cellar
was the same as the soil-gas radon concentration in the surroundings of the building. In
addition, very fast changes of indoor radon concentration were also observed.
In 2005, remedial measures were performed byfirst replacing the timber floors with a concrete
slab fitted with a damp proof membrane, thermal insulation, and floor covering A sub-slab
ventilation system consisting of two independent sections was then installed. The
effectiveness of remedial measures is illustrated in Fig. 3.
50000

-3
cR n (Bq.m
)

40000

30000

20000

10000

0
7.10.04 8.10.04 9.10.04 10.10.04 11.10.04 12.10.04 13.10.04 14.10.04 15.10.04
12:00
12:00
12:00
12:00
12:00
12:00
12:00
12:00
12:00

Fig. 2. Continual measurement of indoor radon concentration in the living room - before remediation.

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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

6000

5000

-3
cR n (Bq.m
)

4000

3000

2000

1000

0
4.8.05 6.8.05 8.8.05 10.8.0512.8.05 14.8.0516.8.0518.8.0520.8.0522.8.0524.8.05
0:00 0:00 0:00 0:00 0:00
0:00 0:00 0:00 0:00 0:00 0:00

Fig. 3. Continual measurement of indoor radon concentration in the living room - after remediation. Ventilation
experiment - 4.8. 8.45 - 11.8. 9.30: gradual start of the 1st section;
11.8. 9.30 - 18.8. 10.15: both sections in operation (maximum power); 18.8. 10.15 - 22.8. 12.00: ventilation
switch-off.

The Weakest Link- The Human Factor
The Radon programme in the Czech Republic has a long and rich history.
By using using different remedial measures procedures, we are able to evaluate the risk of
radon penetration from the ground, and protect residents of both new and existing buildings
from elevated indoor radon levels. These remedial measures and procedures, have been
developed, published, field tested and are being applied successfully today.
Although, this approach is sound (if it is performed correctly, the odds of a successful radon
remediation is very high). Problems do exist because of simple human error, or
misperceptions caused by psychological, or sociological reasons (Neznal, 2008). Two
examples follow.
Example A: It is known that the indoor radon concentration significantly changes in time and
that it may be strongly influenced by inhabitant’s behaviour. Therefore radon measurements
using intergrating devices are the most common. Unfortunately, and all too often, these
devices are placed and retrieved by untrained nonspecialists. In addition, the residents either
knowingly, or unknowingly, too often do things out of malice or ignorance that can have a
significant impact on the radon measurement. The following lists the spectrum of human
related problems:
- Poor selection of a testing location: The detectors are located in rooms that are declared as
habitable rooms (living rooms), but used for other purposes (as storerooms).
- Inappropriate time to test: The testing was being performed during a period of long-term
floor reconstruction.

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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

Resident variables such as:
- people want „to avoid any problems“ (increased ventilation),
- people want to get financial support from the government (reduced ventilation),
- people like „experiments“, and
- people want „to safe money“ (and switch-off the sub-slab ventilation system).
Example B: The radon programme is directed by central institutions with the goal to decrease
a collective dose. Therefore, a conflict between the individual and an all-society“ points of
view is inevitable. However, in some cases remediation may not be recommended. For
example, the benefit of the remediation of homes occupied by the elderly may be off set by
the stress and discomfort that remedial actions may cause.

Conclusion
A summary of experiences resulting from the Czech Radon Programme has been presented.
Disscusion and conclusions relating to partial problems are included in separate scientific
papers (See References).

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Proceedings of the American Association of Radon Scientists and Technologists 2008 International Symposium
Las Vegas NV, September 14-17, 2008. AARST © 2008

References
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daughters. - Radiation Protection Dosimetry, 7, 1-4, 49-54.
Bale, W.F. (1951): Hazards associated with Radon and Thoron. Memorandum to the files.
March 14, 1951. - Health Physics, 38, 1062-1066.
Barnet, I.; Kulajta, V.; Matolín, M.; Veselý, V. (1990): A proposal of the radon risk
classification of foundation soils. In: Barnet, I. ed. Radon investigations in CS. Vol. 1. Praha Geological Survey, 24-28.
Barnet, I. (1994): Radon risk classification for building purposes in the Czech Republic. In:
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Barnet, I.; Pacherova, P.; Neznal M.; Neznal M. (2008): Radon in geological environment Czech experience. - Czech Geological Survey Special Papers 19, Praha: Geological Survey.
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Las Vegas NV, September 14-17, 2008. AARST © 2008

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