Friderik Knez

Department for Building Physics

friderik.knez@zag.si

Dresden, 2. - 3. December 2013

Radon protection conference

• Central European country

• 2 million inhabitants

• 3 climatic regions

– Snow in winter

– Medium rain

• Neighbouring

– Croatia

– Italy

– Austria

– Hungary

• Left: known caves

• Right: terrain type, regarding permeability

• Systematic research

for some 20 years

• Shown: ground radon

potential

• Detailed surveys of

indoor radon in

schools and

kindergartens

• 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

• Before 1945 – CE

• 1945-1970 – brick, poor

practice

•

1970-1980 gradual

improvement

•

Rdon risk is found particularly

in class 1 and 2 SHF

• 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

• 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)

• Blueprints analyses

• Studying

measurements

• Interview employees and locals

• Measurements and assessment

• Design a strategy

• Apply a pilot system

• Evaluate effect

• Correct if neccesary

• Finalize the system

• Different sources (older

users, maintenance

personell, historic

sources)

– Ussually more reliable than

old blueprints!

• Local information

– Materials

– Debree use

– Geological data

• 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

• Permeability measurements

• Sometimes no pressure communication is found

– Very tight or very loose structure

• Crucial in air pressurization systems

• May predict effects of energy

refurbishment

• 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)

• Fan selection

• Controll absence

• Change of piping material

• Caulking material

Janče

Wooden floor, fly-ash in

the structure.

Fly ash in the

floor structure

Over 1.000

less than

400

-

1997

SSD

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

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)

Prevole

Concrete, inaccessible

walls

Soil

3.200

Not yet

avail.

-

2012

SSD

Muljava

Concrete floor on ground,

under floor suspected

mixed debris

Soil

4.000

380

-

2011

SSD

Vavta vas

Concrete (?), stone walls,

under floor suspected

debris

soil

1.750

340

169

2013

SSD, sealing

• 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

• 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

)

•

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

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

• 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

• 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

• 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

• 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

• 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

• 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

42

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

• 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

•

:

Common problem with

durability of radon mitigation solution is that in most of the cases

additional interventions were done.

•

: radon mitigation

system properly executed, however instructions for use not

respected. The system was not operated continuously.

•

In some cases the radon mitigation system was

improperly executed due to lack of understanding of the purpose of

individual components.

•

user of the building does not feel any need for further

considering concentration monitoring.

• 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

• 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