MOD EL LING RA DI A TION EX PO SURE IN HOMES FROM
SIPOREX BLOCKS BY US ING EX HA LA TION RATES OF RA DON
by
Mladen D. NIKOLI] 1,2*, David R. SIMOVI] 2, Milija ZE^EVI] 3, and Violeta V. CIBULI] 2
1
Col lege of Ap plied Tech ni cal Sci ences, Kruševac, Ser bia 2
Un ion – Nikola Tesla Uni ver sity, Bel grade, Ser bia 3
Eu ro pean Uni ver sity, Bel grade, Serbia
Sci en tific pa per DOI: 10.2298/NTRP1504301N
Build ing ma te ri als are the sec ond ma jor source of in door ra don, af ter soil. The con tri bu tion of build ing ma te ri als to in door ra don amount de pends upon the ra dium con tent and ex ha la -tion rates,which can be used as a pri mary in dex for ra don lev els in the dwell ings. This pa per pres ents the re sults of us ing the ex per i men tally de ter mined ex ha la tion rates of siporex blocks and con crete plates, to as sess the ra di a tion ex po sure in dwell ings built of siporex blocks. The an nual doses in rooms have been es ti mated de pend ing on the es tab lished modes of ven ti la -tion. Re al is tic sce nario was cre ated to pre dict an an nual ef fec tive dose for an old per son, a house wife, a stu dent, and an em ployed ten ant, who live in the same apart ment, spend ing dif -fer ent pe ri ods of time in it. The re sults in di cate the cru cial im por tance of good ven ti la tion of the liv ing space.
Key words: ra don, ex ha la tion rate, ra di a tion ex po sure, siporex, con crete, mod ell ing
INTRODUCTION
Ra don (222Rn) and its prog eny are pres ent in all dwell ings, be cause ra dium is pres ent in build ing ma te -ri als as well as in the soil. It is im por tant to un der stand the gen er a tion and mi gra tion pro cess of ra don from build ing ma te ri als, which con trib utes to 55% of to tal ra di a tion dose re ceived by the pop u la tion from the en -vi ron ment [1]. A re search, deal ing with the ra di a tion ex po sure in duced by ra don de cay prod ucts in homes, has shown that the cause of in creased ra di a tion may as well be the con struc tion ma te rial of the build ing. When es ti mat ing an av er age an nual ra di a tion ex po -sure, one should also take into ac count life at home, be cause the level of ra di a tion can be higher within homes than out side, bear ing in mind that the walls them selves can con tain and emit radionuclides. De -pend ing on the type of the con struc tion ma te rial and ven ti la tion ef fi ciency [2, 3], ra di a tion in doors can be many times higher than out door, and as such, it rep re -sents a se ri ous health haz ard. The av er age an nual dose in Eu rope from ra don and its prog eny, in homes and workplaces, is es ti mated to be 1.6 mSv.
In or der to de ter mine ac tiv ity con cen tra tion of ra don in siporex blocks and con crete, ex ha la tion mea -sure ments were per formed by a closed cham ber method [4, 5] and then used to cal cu late an nual doses
in dwell ings made out of siporex blocks. Im pact of ra -don con cen tra tion ac tiv ity from the con struc tion ma te rial, on an nual doses, de pend ing on the es tab -lished ven ti la tion mode, has been an a lyzed. Since the main source of ra don and its prog eny is soil, this sim u -la tion should con sider only apart ments on higher floors in a mod ern res i den tial build ing [6, 7].
De pend ing on the es tab lished mode of ven ti la -tion, the ra don ac tiv ity con cen tra tions and the an nual ef fec tive doses in rooms, have been es ti mated. Four sce nar ios for dif fer ent types of ten ants were cre ated to pre dict the dose re ceived by an old per son, a house -wife, a stu dent, and an em ployed ten ant, who live in the same apart ment.
BASIC DATA NECESSARY FOR THE DOSE ASSESSMENT IN HOMES
Siporex and concrete exhalation rates
of the ac cu mu la tion cham ber and the back dif fu sion rate, is widely used in the mea sure ment of the ra don ex -ha la tion rate of build ing ma te ri als [10-12]. On the other hand, for ap pli ca tion of this method, it is nec es sary to con duct ac tive, con tin u ous mon i tor ing of ra don con -cen tra tion in side the cham ber [5, 12, 13].
The ra don ex ha la tion rate E (Bqm–2h–1) is de fined as the quan tity of ra don ac tiv ity lib er ated from the sur -face area of build ing ma te ri als per unit of time. Us ing this value and the area of the in door sur face, ra don em a nated per unit of time could eas ily be cal cu lated and ap plied to es ti mate the ra don con cen tra tion in the in door en vi ron -ment. Ra don ex ha la tion rates of siporex and con crete were de ter mined by al ready de vel oped closed cham ber method with ac tive con tin u ous ra don mea sure ment tech -nique [5]. Mea sure ments were per formed by means of cer ti fied Safety Si ren ra don de tec tors (Fam ily Safety Prod ucts Inc.). As pre vi ously stated, the closed cham ber method takes into con sid er ation two main fac tors that could in flu ence the ex ha la tion rates. By check ing both of the fac tors, it was found that back dif fu sion can be ne -glected and the cham ber leak age l, which can be de
-scribed by the rate of cham ber's ven ti la tion, was ob tained to be l= 0.0028 h. This value agrees well with the pre vi
-ously pub lished data for closed cham bers, with vol umes of up to 1.5 m3 [13, 14].
In or der to elim i nate mois ture con tent, the siporex and con crete sam ples were dried in an oven at 110 ºC and then put into com part ments un til sat u ra tion time oc curred (57 days). Us ing a tech nique, pre vi ously de vel -oped to mea sure the ra don ex ha la tion rates of gran ites, with an accepteble level of con fi dence [5, 15], the ex ha -la tion rates for siporex and con crete were de ter mined to be E
s = 0.212 ± 0.03 Bqm–2h–1 and Ec = 0.210 ±
±.0.03 Bqm–2h–1, re spec tively.These data are in good agree ment with the mean val ues of the ex ha la tion rates ob tained by mea sure ments per formed with an on line ra -don mea sur ing de vice, for 104 sam ples of con crete and 14 sam ples of siporex (aer ated con crete) [16].
Building materials and dwelling model
In fig. 1, we pres ent a sim pli fied model of a home with the ba sis of 48 m2, whose walls are built of
siporex blocks 0.25 m thick and 0.6 g/cm3 dense, while floors and ceil ings are made of a 2.3 g/cm3 dense con -crete.
The as sump tion is that the home con sists of four rooms: bed room, liv ing room, ves ti bule, and bath -room and the height of the apart ment is 2.2 m. In the cen ter of each room, there is a re cip i ent (ten ant) who spends some re quired time in it. Ta ble 1 shows room di men sions as well as to tal walls sur face and vol umes of the rooms.
Radon activity concentration
Ra don ac tiv ity con cen tra tion C
Rn orig i nat ing from siporex and con crete can be cal cu lated di rectly as [1, 13]
C EA
V
Rn = l n
(1)
where E is the ra don ex ha la tion rate for siporex or con -crete, A – the to tal sur face of siporex wall in the rooms, or the sur face of ceil ings and floors made of con crete, V – the vol ume of the room, and ln – the room ven ti la -tion rate.
In this way, ra don ac tiv ity con cen tra tion was cal cu lated for each room by us ing ex per i men tally ob -tained val ues of the ra don ex ha la tion rate E for siporex and con crete, and the to tal ac tiv ity con cen tra tion for a room is de ter mined as the sum of the con cen tra tions orig i nat ing from siporex blocks and con crete, sep a -rately. For each room, ra don ac tiv ity con cen tra tions are ob tained by chang ing air ven ti la tion rate ln(fig. 2).
Table 1. Dimensions of the rooms
Room type dimensions [m]Room Total windows and doorssurface [m2] made of siporex [mTotal walls surface2] Total floor and ceiling surfacemade of concrete [m2] Room volume[m3]
Living room 4 ´ 5 4.39 35.21 40 44
Bedroom 4 ´ 3 4.92 25.88 24 26.4
Vestibule 2 ´ 5 5.54 25.26 20 22
Bathroom 2 ´ 3 2.37 19.63 12 13.2
In the lit er a ture, the air ven ti la tion rates range from 0. 2 per h to 2 per h, while the av er age value is 0.63 per h [13]. In this pa per,for es ti ma tion of ex po sure to ex hal ing ra don, 17 room ven ti la tion rates were used in the range from 0.001 per h to 1 per h.
DOSE ASSESSMENT
Calculation of the annual effective dose
The an nual ef fec tive dose H, re ceived by ten ants, due to in ha la tion of ra don orig i nat ing from build ing ma te rial, has been cal cu lated by the fol low ing ex -pres sion [1, 14]
H=C ´ ´ ´DCF
Rn F O (2)
where F is the ra don equi lib rium fac tor (0.4), O – the oc -cu pancy fac tor ex pressed as the to tal num ber of hours which the in hab it ant spends in the room in one year, and DCF – the dose con ver sion fac tor (9 nSv/Bqm3 for ra
-don).
For each room, the an nual ef fec tive dose H is de -ter mined by chang ing the air ven ti la tion mode, wherein for each mode of ven ti la tion, three dif fer ent pe ri ods of time, spent by ten ants in a spe cific room, were as sumed. The ob tained re sults for an nual equiv a -lent dose, in each room, are pre sented in fig. 3(a-d).
Fur ther more,the an nual ef fec tive dose in rooms, for the two res i dence times (2 h and 10 h) and for the min i mum (ln= 0.001 h), av er age (ln = 0.63 h), and
max i mum (ln =1 h) ven ti la tion modes, is cal cu lated
and pre sented in tab. 2.
It is ev i dent from tab. 2 that the mode of ven ti la -tion has the big gest im pact on the an nual ef fec tive dose re ceived by a ten ant. Thus, at the min i mum ven ti -la tion (ln = 0.001 h) and for a mod est time pe riod of
two hours a day, spent in the room, the an nual dose ex -ceeds per mis si ble level of 1 mSv per year in ev ery room, ex cept for the liv ing room where it is at the edge of the per mit ted level (0.948 mSv). The an nual ef fec -tive dose pro por tion ally in creases with pro longed stay in a room. How ever, even with the me dium in ten sity of ven ti la tion (ln = 0.63 h), the an nual dose re ceived by a
ten ant be comes neg li gi ble re gard less of the time spent in any room.
Calculation of dose depending on the four tenant scenarios in apartment
In tab. 3, the four sce nar ios for dif fer ent types of ten ants are pre sented, as sum ing that each of them spends an ap pro pri ate pe riod of time in ev ery room of the apart ment and a part of the day out side of home. On this ba sis, the min i mum, av er age, and max i mum an -nual doses re ceived by ten ants dur ing their stay in the apart ment are cal cu lated cor re spond ing to the max i -mum, av er age, and min i mum air ven ti la tion.
We can see, from tab. 3, that the high est dose will be re ceived by an old per son, who spends 22 hours in the apart ment and 2 hours out side, fol lowed by a house wife who spends only 3 hours out side the apart -Fig ure 2. De pend ence of the ra don ac tiv ity con cen tra tion
on ven ti la tion rate
ment. The low est an nual ef fec tive doses in both modes of ven ti la tion will be re ceived by an em ployed per son and a stu dent, in agree ment with the max i mum num ber of hours spent out side home. In ad di tion, it is con firmed that in the hy po thet i cal sit u a tion of the apart ment with out ven ti la tion, the an nual doses sig nif i -cantly ex ceed the per mis si ble level of 1 mSv, while in case of good ven ti la tion the doses can be ig nored.
CONCLUSION
The an nual ef fec tive dose re ceived by a ten ant liv ing in res i den tial pre mises built from siporex blocks is in the ac cept able limit if the mod er ate ven ti la tion is pro vided. The re sults have pointed out the ne ces sity of a reg u lar ven ti la tion of apart ments, by means of air ex -change with the en vi ron ment, in or der to re duce the an nual ef fec tive dose and so the threat to the health of the ten ants.
AUTHORS’ CONTRIBUTIONS
The ex per i ments and cal cu la tions were car ried out by M. D. Nikoli} and manu script was writ ten by M. D. Nikoli} and D. R. Simovi}. All au thors an a lyzed re sults and par tic i pated in prep a ra tion of the fi nal ver -sion of the manu script.
REFERENCES
[1] ***, United Na tions Sci en tific Com mit tee on the Ef -fects of Atomic Ra di a tion, UNSCEAR 2000 Re port to the Gen eral As sem bly, Vol. I: Sources UNSCEAR Sec re tar iat, Vi enna In ter na tional Cen tre
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[3] Hintenlang, D. E., Al-Ahmady, K. K., In flu ence of Ven ti la tion Strat e gies on In door Ra don Con cen tra tions Based on a semiemperical Model for Florida-Style Houses, Health Phys ics, 66 (1994), 4, pp. 427-432
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[9] Sahoo, B. K., et al., A Model to Pre dict Ra don Ex ha la -tion from Walls to In door Air Based on the Ex ha la -tion from Build ing Ma te rial Sam ples, Sci ence of the To tal En vi ron ment, 409 (2011), 13, pp. 2635-2641
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(2001), 1-3, pp. 109-118
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[13] Uji}, P., et al., In ter nal Ex po sure from Build ing Ma te -ri als Com pared to Ex ter nal Ex po sure Due to Ex hal ing
1 0.001 0.001 0.001 0.001
10
0.001 4.74 5.71 5.24 6.65
0.63 0.008 0.009 0.008 0.011
1 0.005 0.006 0.005 0.007
Table 3. Scenario and doses for tenants in apartment
Tenant Old person Student Housewife Employed person
Living room 10 h 6 h 8 h 3 h
Vestibule 1 h 1 h 2 h 1 h
Bathroom 1 h 2 h 3 h 1 h
Bedroom 10 h 9 h 8 h 9 h
Period outside 2 h 6 h 3 h 10 h
Annual effective dose [mSv]
Minimum 0.011 0.009 0.011 0.009
Average 0.01 0.01 0.01 0.01
222
Rn and 220Rn aseir Nat u ral Ra dio ac tiv ity Con tent.,
Ap plied Ra di a tion and Iso topes, 68 (2010), 1, pp. 201-206
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Mea sure ment, Nucl Technol Radiat, 29 (2014), 4, pp. 279-284
[16] Keller, G., Hoffmann, B., Feigenspan, T., Ra don Per me abil ity and Ra don Ex ha la tion of Build ing Ma te ri -als, Sci ence of the To tal En vi ron ment, 272 (2001), 1-3, pp. 85-89
Re ceived on No vem ber 6, 2015 Ac cepted on De cem ber 22, 2015
Mladen D. NIKOLI], David R. SIMOVI], Milija ZE^EVI], Violeta V. CIBULI]
MODELOVAWE IZLAGAWA ZRA^EWU U STANOVIMA OD SIPOREKSA POMO]U JA^INE EKSHALACIJE RADONA
Gra|evinski materijali predstavqaju posle zemqi{ta drugi najva`niji izvor radona u zatvorenim prostorijama. Doprinos gra|evinskih materijala koli~ini radona u prostorijama zavisi od sadr`aja radijuma u wima i ja~ine ekshalacije, te su oni primarni ~inioci koji doprinose nivou radona u stanovima. U ovom radu prikazani su rezultati kori{}ewa eksperimentalno odre|enih ja~ina ekshalacije siporeks blokova i betonskih plo~a radi procene izlo`enosti zra~ewu u stanovima izgra|enim od siporeks blokova. Odre|ene su godi{we doze u prostorijama u zavisnosti od ostvarenog na~ina ventilacije. Na osnovu pretpostavqenog realisti~nog scenarija boravka procewene su godi{we efektivne doze za staru osobu, doma}icu, u~enika i zaposlenog uku}ana, koji `ive u istom stanu provode}i u wemu razli~ito vreme. Rezultati ukazuju na su{tinski zna~aj dobrog provetravawa stambenog prostora.
