Radon mitigation in
Slovenia
Friderik Knez
Department for Building Physics
friderik.knez@zag.si
Dresden, 2. - 3. December 2013
Radon protection conference

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Slovenia – General data
• Central European country
• 2 million inhabitants
• 3 climatic regions
– Snow in winter
– Medium rain
• Neighbouring
– Croatia
– Italy
– Austria
– Hungary

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Slovenia and karst terrain
• Left: known caves
• Right: terrain type, regarding permeability

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Meaurements of radon in Slovenia
• Systematic research
for some 20 years
• Shown: ground radon
potential
• Detailed surveys of
indoor radon in
schools and
kindergartens

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Buildings
• Building stock
– Approx. 600.000 buildings, 500.000 single houses
– Age varies
– Building type – typical for Central Europe
• Influencing building parameters:
– increase of tightness,
– increase of indoor temperature

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Typical building stock
• Before 1945 – CE
• 1945-1970 – brick, poor
practice
1970-1980 gradual
improvement
Rdon risk is found particularly
in class 1 and 2 SHF

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Mitigation
• Serious mitigation for 20 years
• Sources
– Karst terrain
– High U content in soil
– Fly ash
• Based on EPA guidelines
• Readon prevention – new build: (only) 3 cases
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Friderik Knez | Radon protection conference , 2. -3. september 2013

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Current changes in buildings
• Energy efficiency measures cause
– Tighter envelopes
– Controlled ventilation / over- or underpressure
• Genaral situation
– Lower awareness of risks generally (radon, earthquake, flood) or
– Denial of rosk
– Mobility and real estate prices push buildings on riskier areas
(e.g. South of Ljubljana)

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Cases

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Radon source per case
Fly ash
Soil
Cases
Prevention

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Cases – general workflow applied
• Blueprints analyses
• Studying
Rn
measurements
• Interview employees and locals
• Measurements and assessment
• Design a strategy
• Apply a pilot system
• Evaluate effect
• Correct if neccesary
• Finalize the system

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Listening to the employees
• Different sources (older
users, maintenance
personell, historic
sources)
– Ussually more reliable than
old blueprints!
• Local information
– Materials
– Debree use
– Geological data

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Knowing what you are dealing with
• Ussually needed
intervention
– Opening the structure
– Water barrier?
• Often found critical:
knowledge – details on
shafts
– Unexpected difficulties (e.g.
Sealed access)
• Important: detailed
inspection to minimize
intrusion

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Details

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Evaluating planned strategy
• Permeability measurements

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Difficulties
• Sometimes no pressure communication is found
– Very tight or very loose structure

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Evaluation of building tightness
• Crucial in air pressurization systems
• May predict effects of energy
refurbishment

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Different strategies considered
• Local underpressure
– SSD (“sub-slab depresurisation”) – often
used in Slovenia
– SMD (“sub-membrane depresurisation”) –
very seldom used in Slovenia, results not so
good
– DTD (“drain – tile” depressurisation) – never
used in Slovenia as is originally designed
– Drain / shaft system – used if posible,
results are good
• Overpressurization
– Considered in latest case (not presented)

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Systems execution – different
variations

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Critical in execution (found)
• Fan selection
• Controll absence
• Change of piping material
• Caulking material

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Mitigation principle used in selected
cases

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Results of mitigation
#
Building
Basic building
description
Radon source
C
Rn,initial
[Bq/m
3
]
C
Rn,inter
[Bq/m
3
]
C
Rn,mit
[Bq/m
3
]
Mitig.
[year]
Mitig. principle
1
Janče
Wooden floor, fly-ash in
the structure.
Fly ash in the
floor structure
Over 1.000
less than
400
-
1997
SSD
2
Lokev pri
Sežani
Wooden floor, beneath
large void (estimated 1,5
m
3
/m
2
floor)
Soil
> 1.000
200-850
-
1997
New floor, SSD
3
Dolenja vas
Concrete floor, long shaft
network (piping, sewage)
Soil, radon
distributed by
shafts
600-4.150
100-3.165
< 100 - 500
1997
Ventilation of
shafts + SSD
(part)
4
Prevole
Concrete, inaccessible
walls
Soil
3.200
Not yet
avail.
-
2012
SSD
5
Muljava
Concrete floor on ground,
under floor suspected
mixed debris
Soil
4.000
380
-
2011
SSD
6
Vavta vas
Concrete (?), stone walls,
under floor suspected
debris
soil
1.750
340
169
2013
SSD, sealing

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Janče
• Radon source is fly
ash in void
• Minigation: removal of
fly-ash and ventilation
• Concentration
reduction
– Before:1020 Bq/m
3
– After: < 400 Bq/m
3

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Lokev pri Sežani
• Large void in structure
• Floor reconstructed
– Drainage system
introduced
• Ventilation in chimney
• First operation
successful, but fan
failure due to poor fan
selection
• Secon operation very
successful (C
Rn
< 200
Bq/m
3
)

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Case Dolenja Vas (1997)
Initial: 600 - 4000 Bqm
-3
Final: 100 – 500 Bqm
-3
First mitigation: shaft
ventilation
Second mitigation:
extension
Third mitigation:new
exhaust

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Dolenja vas
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Friderik Knez | Radon protection conference , 2. -3. september 2013

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Case Dolenja vas (revisited)
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Friderik Knez | Radon protection conference , 2. -3. september 2013

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Dolenja vas - revisited
• Mitigation successful when commissioned
• Some modifications done afterwards (facade –
air feed-in due to lack of understanding)
• New floor in library
– Problems with sealed floor (seen very soon)
• Effect of modifications on mitigation system not
known
• Change of personell dilutes instructions passed
at set-up

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Divača („impossible case“)
• Railway controll room
• Radon entering via large floor opening
• Opening connected to underground signalization
system
– No modification allowed due to safety reasons
– Underground „collector“ about 5 km long – no
ventilation or overpressure is possible
• Solution:
– Instant: increased natural ventilation
– Discussed (but not realized): mechanical ventilation
with overpressure scheme

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Divača

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Ribnica („impossible case 2“)
• School exhibits high concentrations
• Analyzing blueprints following is found
– The building lies on 140 cm thick concrete
– Reason: pit beneath, leading into minor karst cave
• Exploring the possibilities it becomes clear:
– No SSD possible due to very high volume to be vetilated
– No overpressure possible due to central position of rooms
in question
– Sealing virtually impossible in technical rooms due to
installations
• Solution:
– Limited access and use of rooms
– Exploring possibilities for ventilation via shafts

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Ribnica

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Case Muljava (2010-2011)

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Case Muljava

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Muljava – sum up
• Concentration
– Before 4000 Bqm
-3
– After 380 Bqm
-3
• The system in crucial points as designed
• Alterations in material selection
– Increased drag
– Possible issues on durability / condensation
• No monitoring has been installed to monitor pressure
– Risk of unnoticed failure
• Results of contol measurements OK

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Prevole (2011-2012)

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Prevole - analyses

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Prevole

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Prevole – sum up
• Mitigation strategy was prepared
• Due to small space problems with execution
were expected
• The owner modifeid mitigation strategy
– Without notice or consultation
– Reason claimed: mainly difficul accessibility
• Real problems:
– Lack of understanding the princliples of thy system
– Unskilled technical personell in the building
– Distributed tasks
– Organization of school system

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Prevole - expectations
• Measurements not yet done
• Expected insufficient effect in spite of obvious
effect of the ventilator
– We hava assessed that the vent is simply moving
outside air
• Inspectorate is alerted about the intervention

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Case Vavta vas (2012-2013)

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Case Vavta vas
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Friderik Knez | Radon protection conference , 2. -3. september 2013

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Vavta vas – sum up
• Concentration dropped
– Before: 1750 Bqm
-3
– After: 170 Bqm
-3
• Whole solution approach
– Design
– Pilot installation
– Unofficial measurements
– Recommendations for improvements
• The system exhibited unexpected behaviour at first
• After adjustement good results
• However: due to lack of concern
– No official measurements ordered so far
– No proper commissioning done
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Friderik Knez | Radon protection conference , 2. -3. september 2013

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Identified risks
Risk 1
:
unauthorized interventions:
Common problem with
durability of radon mitigation solution is that in most of the cases
additional interventions were done.
Risk 2: failure to operate system properly
: radon mitigation
system properly executed, however instructions for use not
respected. The system was not operated continuously.
Risk 3: failure to comply fully with instructions for system
execution:
In some cases the radon mitigation system was
improperly executed due to lack of understanding of the purpose of
individual components.
Risk 4: users rely on mitigation system without further
measures:
user of the building does not feel any need for further
considering concentration monitoring.

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Essential measures
• Based on experience following is particularly
imporatnt:
– Radon mitigation has to be done by professionals all
the way (design to execution)
– Good commisioning and maintenance is essential
– Clear guidelines for radon prevention are needed
• Radon maps
• Legislation
• User guides
– It seem that awareness in general public has to be
high or systems will fail

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Conclusions
• Radon can be successfully mitigated
• Plenty of mitigation knowledge available
• However there are „impossible“ cases as well
• Successful rate is high, however:
– Seldom concentration is not elevated at all
– Difficult to explain problems often occure, e.g.:
Rock in soil
• Cracked and permeable walls
• Higher concentration at 1
st
floor in comparison to ground floor
• Identified risks pose big threat to overall success

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Thank you for your attention!