Measurement in schools and

kindergartens in different town and

regions in Bulgaria

Kemena Ivanova

Sofia Bularia

National Center of Radiobiology and Radiation Protection – Ministry of Health

Bulgarian legislation –

Regulation on Basic Norm of Radiation Protection

Article 45 (1) The equivalent dose rate of gamma radiation in buildings, public buildings, industrial and other buildings should not exceed the local dose rate outdoors by more than 0,2 µSv/h.

• (2) reference levels for limiting exposure to radon are:

▫ 1. annually averaged radon concentration in the air - 200Bq.m-3

for new residential and public buildings;

▫ 2. annually averaged radon concentration in the air - 300 Bq.m-3

for existing residential and public buildings;

▫ 3. average radon concentration in the air - 1000 Bq.m-3 jobs.

• (3) In specific cases where the duration of occupancy in existing public buildings is small, the Minister of Health may determine for an annual average concentration of radon in the air a reference level more than 300 Bq.m-3, but not more 1000 Bq.m-3

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Pilot Study in schools and kindergartens

• Method – passive measurement(E-Perm system)

• Short-term and long–termmeasurements

• Period - August 2011 to April2012 (short–term- 1 week, long-term – 6 month)

• Investigated area - Kremikovtsiregion of Sofia district (close toformer uranium mining andmilling industry)

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1-st Stage - Short-term measurements of ground floor

>300 Bq m-3

Yes

2-nd Stage – Follow-up measurements

Short-term measurementsLong-term measurements

> 300 Bq m-3 ≈ 300 Bq m-3

>300 Bq m-3 >300 Bq m-3

Reducing the level of radon Reducing the level of radon

Control measurements

No

Yes Yes

No No

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Pilot Study – method (strategy)

Pilot study - steps

• 1-st stage - screening measurements

omeeting with the school’s manager

o short-term measurement during the summer vacationunder closed conditions

o all classrooms occupied the ground floor and basementwas measured.

• 2-nd stage – follow-up measurements

o Long-term measurement depending on the result above than or approximately equal to referent level of 300 Bq.m-3.

• 3-th stage – control measurements after reducing the Rn-concentration

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Short-term Long-term

No. of premises 98 24

School 9 4

Kindergarten 7 4

Minimum CRn (Bq m-3) 32 104

Median CRn (Bq m-3) 196 463

Maximum CRn (Bq m-3) 1305 1761

AM CRn (Bq m-3) 339 694

SDV CRn (Bq m-3) 315 504

GM CRn (Bq m-3) 220 542

GSDV 2.59 2.06

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Pilot study - Results

• Relationship between short and long termmeasurements - linear regression between short-term and long-term measurements

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Pilot study - Results

y = 1.2204x - 1.1253

R2

= 0.668

R = 0.817

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4.5

5

5.5

6

6.5

7

7.5

8

4.5 5 5.5 6 6.5 7 7.5

ln CRn(Bq/m3)-short

ln C

Rn(B

q/m

3)-

long

Observations Predictions Conf. on pred (95.00%) Conf. on mean (95.00%)

• The post-mitigation measurements wereperformed in October 2012 in 24 premises of all9 buildings with EICs passive integratingdetectors for 1 month

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Pilot study – Results of control measurement

Results of CRn measurements before and after mitigation

• Assessment of effectiveness of these measures the criteria of efficiency are used.

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Pilot study – Results of control measurement

0

20

40

60

80

100

R [%]

1-S 2-S 3-S 4-S 1-K 2-K 3-K 4-K 5-K

Public Buildings

Reduction efficiency

after

befor

C

CRF =

reduction factor RF

Reduction efficiency in 5 buildings is above 70%, in the other buildings is below this rate.

• The obtained results for schools and kindergartenswere higher, mainly due to location close to uraniummining and milling sites.

• Higher radon concentrations were observed inkindergartens than in schools because of differentbuilding characteristics.

• The comparison between the measurementsperformed by short and long term detectors,confirms the reliability of the short termmeasurements.

• Radon sources, radon concentrations and radontransport mechanisms should influence on thechoice of mitigation strategies.

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Pilot study – Lesion learn

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Systematic measurement in kindergartens in Sofia- city

• Number of buildings - all public kindergartens according the national information system – 296 buildings

• Number of premises – 922 rooms, which situated:

• at the ground floor situated directly on the ground or above unoccupied (basements, crawlspaces, or utility tunnels)

• the constantly occupied underground rooms (kitchen, swimming pool etc.).

• Period - from February to April 2013

• Method – alpha – tract detectors Radosys systems

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Systematic measurement - distribution of detectors

• The first step - collecting theinformation about the number ofrooms on ground floor, by telephone.

• The second - preparing a packagewith the detectors, instruction forms,brochures and questionnaires.

• The third – gathering kindergartenmanagers by Sofia-city mayoralty forreceiving the packages andinstruction.

• The fourth – in 7 % of kindergartenswere distributed duplicate and on-site inspection.

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Systematic measurement in Sofia city -results

1400120010008006004002000

700

600

500

400

300

200

100

0

CRn [Bq/m3]

Frequ

en

cy

The measured data can be well described by a log-normal function.

CRn [Bq·m-3]

Number of rooms 922

Minimum 9

Median 98

Maximum 1415

Arithmetic mean 132

Standard deviation 118

Coefficient of variation (CV=SD/AM) 0.89

Geometric mean 101

Geometric standard deviation 2.08

Descriptive statistic of indoor radon concentrations in kindergartens

Results of Pilot Radon Survey in dwellings for Sofia city is 78 Bq.m-3.

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Factor Factor data subset

CRn [Bq·m-3]

N Min. Med. Max. GM GSD

Region West 172 25 101 940 116 1.97

East 222 15 100 1415 105 2.14

North 116 11 102 433 101 2.18

Central 301 10 87 739 93 1.96

Southern 109 9 103 779 91 2.27

West – violet

East - red

North – green

Central – orange

Southern - rose

Systematic measurement in Sofia city -results

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Factor Factor data subset

CRn [Bq·m-3]

N Min.Med

.Max

. GM GSD

Building materials

Bricks 420 20 109 940 114 1.89

Reinforced concrete 163 10 85 769 95 2.20

Concrete panel 178 11 91 470 89 2.20

Brick + concrete 159 9 80 1415 88 2.20

Buildings built of brick have the higher geometric mean ofCRn than the buildings made of concrete, or reinforcedconcrete, or both.

Systematic measurement in Sofia city -results

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FactorFactor data

subset

CRn [Bq·m-3]

N Min. Med. Max. GM GSD

Presence of foundation

Withoutfoundation 23 48 140 355 135 1.94

with foundation 847 9 95 1415 99 2.09

Presence of basement

Withoutbasement 251 20 139 864 139 1.91

with basement 657 9 85 1415 89 2.07

Higher indoor CRn is in buildings without basement and foundation.

Systematic measurement - results

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Systematic measurement in towns and regions in Bulgaria

• Numbers of towns – Plovdiv, Burgas and Pernik region

• Number of buildings public kindergartens – 91 buildings in Plovdiv; 49 in Burgas and 34 in Pernik region – 174total buildings

• Number of premises – 473 rooms in Plovdiv; 193 in Burgas and 111 in Pernik region – 777 total measurement rooms

• Period – 3 month from January/February to April/May 2014

• Method – alpha – tract detectors Radosys systems

XX

X

Descriptive Statistics

CRn-total

CRn-Plovdiv

CRn-Burgas

CRn-Pernik

Number 777 473 193 111

AM 227 260 212 113

Median 164 200 165 93

SDV 181 193 159 92

Skewness 1.56 1.13 2.70 2.62

Kurtosis 2.52 .86 9.21 9.71

GM 171 197 176 88

Minimum 14 45 59 14

Maximum 1117 1094 1117 631

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Systematic measurement in towns and regions in Bulgaria - results

Results have a lognormal distribution

Results of Pilot Radon Survey dwellings for Plovdiv district is 137 Bq.m-3.

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Systematic measurement in towns and regions in Bulgaria - results

FactorFactor data

subset

CRn [Bq·m-3]

N Min. Med. Max. GM GSD

Renovation of buildings

Renovation 461 14 203 1095 204 2.04

Not renovation 316 21 115 1117 132 2.16

Influence of renovation of buildings on the concentration of radon

The higher radon concentrations is related to buildings which was renovated without taking into account radon concentration (KW, p<0.0001).

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Systematic measurement in towns and regions in Bulgaria - results

FactorFactor data

subset

CRn [Bq·m-3]

N Min. Med. Max. GM GSD

Type of windows

new type(PVC, ect.) 625 14 198 1117 208 1.94

old type (wood etc.) 153 18 69 760 76 1.84

Influence of type of windows on the concentration of radon

The higher radon concentrations is related to buildings with new type of windows (KW, p<0.0001).

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• The distribution of detectors trough majority is easy and quickway.

• Information days of kindergarten's staffs were performed.

• The buildings of kindergartens have higher levels of radonconcentration in comparison with the dwelling.

• The measured CRn were generally higher in buildings madefrom bricks, with new type of windows, without basement andfoundation.

• Renovations of the building and change the old windows withnew one (PVC, ect.) without taking into account theconcentration of radon, may increase the concentration ofradon in the building.

• The measurement protocols is under consideration with theinclusion of direct measurements in buildings with ahigh concentration.

Systematic measurement –conclusions

Pilot study - 2015

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During the weekend

During the week from 14-17.04.2015

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Special thanks to my colleagues from Radon monitoring and prevention laboratory and from Reginal Health Inspectorates who helped me to carry out researches and analysis of results!