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for gen er a l s u r vey wor k is a s m a ll r a d on d iffu sion ch a m b er h ou sin g a p la s t ic a lp h a -t r a ck d e-t ec-t or (Den m a n , 1994). T h is p r ov id es a m ea s u r e of t h e t ot a l r a d on exp os u r e over t h e m ea s u r em en t p er iod . It is t h en p os sible t o ca lcu la t e t h e aver a ge r a d on con cen t r a t ion over t h e m ea su r em en t p er iod .
To en s u r e t h a t t h e r es p on s e is lit t le a ffect ed by d iu r n a l a n d ot h er t im e va r ia t ion s in r a d on , t h e d et ect or s w er e left in p osit ion for on e t o t h r ee m on t h s. Tim e-aver a ged va lu es w er e ca lcu la t ed u s in g N RP B va lu es for s ea -son a l cor r ect ion fa ct or s.
H ou r ly m ea su r em en t s w er e m a d e in r oom s w it h eleva t ed r a d on levels t h a t d is p layed m a r k ed va r ia t ion s (F igu r e 1). T h is occu r r ed over a p er iod of on e t o fou r w eek s u sin g a d ir ect r ea d in g RAD seven m et er (Den m a n a n d P a r k in son , 1996). T h is a ct ively p u m p s a ir sa m p les in t o a m ea su r in g ch a m b er. St a ff w er e a s k ed t o fi ll in a q u es t ion n a ir e t o in d i-ca t e h ow m a n y h ou r s t h ey s p en t in ea ch r oom in a n a t t em p t t o est im a t e t h e occu p a n cy fa ct or. T h e r a d ia t ion d os e t o s t a ff cou ld t h en b e ca lcu la t ed , a n d exp r es s ed a s a n effect ive r a d ia t ion d os e u sin g t h e r ela t ion t h a t 1m Sv is eq u a l t o 126k Bq m–3h ou r s.
T h e a cce p t ed p r ot ocol for r a d on m ea s u r e-m en t in t h e wor k p la ce is t o p os it ion d et ect or s in a s elect ion of gr ou n d fl oor r oom s ch osen t o r efl ect t h e n or m a l occu p a n cy p a t t er n of t h e bu ild in g. In sm a ll p r em ises, a d et ect or is p la ced in ea ch of t h e t wo m os t fr eq u en t ly occu p ied r oom s. In la r ge bu ild in gs on e sh ou ld b e d e p loyed for a t lea st ever y 100m2of fl oor s p a ce. In ver y la r ge, op en bu ild in gs on e sh ou ld b e u sed for ever y 500m2of fl oor a r ea .
Results
N or t h a m p t on s h ir e is a n a ffect ed a r ea a n d eleva t ed levels of in d oor wor k p la ce r a d on a r e t o b e exp ect ed . T h e r es u lt s for d ist r ict s a n d b or ou gh s in N or t h a m p t on s h ir e a r e t o b e fou n d in Ta ble I. In clu d ed in Ta ble I a r e aver -a ge r -a d on v-a lu es in h ou sin g in t h e r e gion s,
t h ese su r vey s a r e ext en sive, b a s ed on a la r ge n u m b er of dw ellin gs, a n d give a n in d ica t ion of p os sible levels in t h e wor k p la ce.
T h e q u a n t it y of d a t a is st ill r ela t ively sm a ll a n d so som ew h a t lim it s t h e con fi d en ce t h a t ca n b e p la ced on it , even so, t h e r a n ge fr om 9 t o 21 p er cen t , clea r ly su ggest s t h a t t h er e is a sign ifi ca n t p r oblem in t h e r e gion . T h ese va lu es a r e h igh com p a r ed t o t h e a p p r oxi-m a t ely 6 p er cen t of t h e sch ools in t h e cou n t y t h a t r eq u ir ed r em ed ia t ion for wor k p la ce r a d on . T h e v a lu e for sch ools is p r ob a b ly r e p r esen t a t ive of t h e s ca le of t h e p r oblem a cr os s t h e cou n t y. Sch ools a r e even ly sp r ea d a n d t h ey r e p r esen t wor k p la ces t h a t d iffer in size fr om t h e s m a ll, s om e 60 p u p ils, t o t h e ver y la r ge, w it h h u n d r ed s of p u p ils a n d la r ge com p lexes of bu ild in gs. T h e r esu lt fr om sch ools, h ow ever, n eed s t o b e t r ea t ed w it h som e ca u t ion a s m ost r oom s a r e q u it e la r ge, bu t in bu ild in gs w it h sm a ller r oom s t h e p r o-p or t ion a b ove t h e lim it m ay b e h igh er. T h e p er cen t a ge for N H S p r op er t ies, a t 8 p er cen t , m ay b e h igh er b eca u se of t h e sign ifi ca n t n u m b er of sm a ller offices. A m or e d et a iled su r vey is u n d er w ay in t h e cou n t y, in a n a t t em p t t o d et er m in e a m or e a ccu r a t e fi gu r e for t h e p r op or t ion a b ove t h e a ct ion level, bu t t h is w ill n ot r e p or t for som e t im e yet .
Ra d on levels ca n va r y m a r k ed ly even w it h in r ela t ively sm a ll a r ea s. T h e va lu es for t h e a r ea cover ed by N or t h a m p t on Bor ou gh a r e p r e-sen t ed a ccor d in g t o p ost cod e in Ta ble II.
N or t h a m p t on s h ir e N H S p r op er t ies a r e w it h in fou r N H S t r u st s, a n d in clu d e t wo gen -er a l h osp it a ls, h ea lt h cen t r es a n d r esid en t ia l h om es, t h e t ot a l n u m b er of p r op er t ies is 82. T h e t ot a l st a ff n u m b er is som e 6,693 w h ole t im e eq u iva len t s. Ou r su r vey h a s t o d a t e m ea su r ed r a d on levels in 1,038 r oom s a n d t h is h a s t h e u s u a l log-n or m a l d is t r ibu t ion w h ich is a lso r e p or t ed in a n u m b er of su r vey s of r esid en t ia l p r em ises w it h 1 p er cen t over 1,000Bq m–3a n d 8 p er cen t over t h e wor k p la ce a ct ion level. Ty p ica l r ea d in gs fr om a bu ild in g w it h r a ised levels a r e fou n d in Ta ble III. T h e r esu lt s for t h e d ist r ibu t ion of r a d on over a ll p r op er t ies a r e fou n d in Ta ble IV.
Table I
Numbe r o f wo rkplac e s te s te d and the pe rc e ntage abo ve the ac tio n le ve l
Average radon
District/ Number Percentage above levels in housing Area
borough tested action level (Bq m–3) Population (ha)
Corby 3 7 1 1 3 8 5 3 ,0 0 0 8 ,0 0 0
Daventry 2 2 8 9 7 4 6 3 ,0 0 0 6 6 ,6 0 0
East Northants 8 0 1 0 6 3 6 8 ,0 0 0 5 1 ,0 0 0
Kettering 1 7 8 1 6 1 0 7 7 7 ,0 0 0 2 3 ,4 0 0
Northampton 1 8 4 2 1 5 5 1 8 1 ,0 0 0 8 ,1 0 0
South Northants 5 2 1 0 6 1 7 1 ,0 0 0 6 3 ,5 0 0
Wellingborough 9 5 1 4 6 6 6 8 ,0 0 0 1 6 ,3 0 0
Table II
Variatio n in rado n le ve ls in c o mme rc ial pre mise s within a bo ro ugh c o unc il (No rthampto n), by po stc o de
Radon Percentage of properties
(Bq m–3) NN1 NN2 NN3 NN4 NN5
0-99 3 3 .6 5 3 .3 5 6 .3 7 5 .0 5 0 .0
100-199 2 3 .5 2 0 .0 1 8 .8 4 .1 2 5 .0
200-399 1 4 .3 0 1 5 .6 8 .3 6 .2
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Sever a l r oom s a r e ver y sm a ll s t or e r oom s t h a t a r e r a r ely en t er ed , t h es e h ave b een d is -cou n t ed a n d w ill n ot b e r em ed ia t ed . A t ot a l of 21 wor k p la ce loca t ion s w er e fou n d t o b e over t h e lim it a n d n eed in g r em ed ia t ion . In a ll, 11 h ave b een s u ccess fu lly r em ed ia t ed a n d t wo r eq u ir e fu r t h er wor k . T h e cost s for t h e r em ed ia t ion for loca t ion s is fou n d in Ta ble V, w h ich a ls o con t a in s d a t a on ot h er t y p es of wor k p la ce loca t ion s in N or t h a m p t on s h ir e.
Loca t ion s w it h levels in exces s of 550Bq m–3 w er e fi t t ed w it h on e or m or e s u m p s a n d ext r a ct or fa n s. T h e t ot a l cos t for t h ese eigh t loca t ion s w a s £39,300. T h e low es t cos t for t h es e loca t ion s w a s £640, h er e a s in gle s u m p, w it h fa n , w a s in s t a lled t o s u cces s fu lly r em e-d ia t e on e s m a ll r oom .
In a n ot h er ca se, w h er e t h e level w a s 430Bq m–3, t h e void b elow t h e bu ild in g w a s fi t t ed w it h a n im p r oved for m of p a s sive ven t ila t ion a s w ell a s a d d it ion a l fa n s t o a ct ively exp el a ir fr om t h e u n d er fl oor void t o t h e ext er n a l en v ir on m en t . T h is w a s con s id er ed su it a ble t o b r in g t h e level b elow t h a t r eq u ir ed by le gisla -t ion . T h e cos-t for -t h is w a s £2,000.
A fu r t h er t wo loca t ion s, w h er e r a d on levels w er e ju s t a b ove t h e lim it , w er e fi t t ed w it h ext r a ct or fa n s on ly in t h e u n d er fl oor void , s u m p s w er e n ot d eem ed n ecess a r y. T h e cost for t h es e w a s £2,150.
As s oon a s a p r oblem w a s d et ect ed a H ea lt h a n d Sa fet y a dv iser w a s con su lt ed . An a ct ion p la n w a s d ev ised a n d t en d er s w er e in v it ed fr om com p a n ies w h o w er e on t h e UK Ra d on Cou n cil’s list of a p p r oved con t r a ct or s. Rem e-d ia l wor k w a s t h en ca r r iee-d ou t , m os t ly w it h in
a p er iod of a r ou n d t h r ee m on t h s. On ly in on e ca se, t h a t of a n office w it h levels of 2,870Bq m–3, w a s it n ecess a r y t o eva cu a t e a n d p r even t st a ff en t er in g.
T h e a n n u a l d ose fr om r a d on in t h e N H S wor k p la ce h a s b een est im a t ed for 64 st a ff w h o wor k in t h e id en t ifi ed h ot sp ot s. T h e d ist r ibu -t ion is sh ow n in F igu r e 3. T h e a n n u a l -t o-t a l collect ive d ose for t h es e s t a ff fr om r a d on w a s 285m Sv, a n aver a ge of 4.45m Sv. Aft er r em ed ia -t ion -t h e aver a ge d os e fell -t o 0.5m Sv.
Discussion
Sim p le est im a t es of d ose t o wor k er s, b a sed on aver a ge r a d on levels, ca n b e m islea d in g. Ra d on levels ca n va r y m a r k ed ly d u r in g a 24 h ou r p er iod (F igu r e 1) w it h t h e h igh est levels a p p ea r in g ou t sid e of st a n d a r d wor k in g h ou r s. As occu p a n cy, on t h e wh ole, d ecr ea ses t h er e is a r ed u ct ion in ven t ila t ion w it h a n in cr ea se in r a d on con cen t r a t ion . As som e or ga n isa t ion s m ay em p loy a n u m b er of sh ift wor k er s a t n igh t t im e, wh o op er a t e in a sed en t a r y m a n -n er, t h er e m ay b e co-n sid er a bly gr ea t er d oses r eceived by t h ese t h a n ot h er s wh o wor k d u r -in g t h e d ay. T h e N HS em p loy s a con sid er a ble n u m b er of n igh t wor k er s a n d t h ese m ay b e a t ext r a r isk . However, it is essen t ia l t o k n ow t h e va r ia t ion s in r a d on levels t h r ou gh ou t a 24 h ou r p er iod a s well a s t h e t im e-aver a ged levels, over p r olon ged p er iod s, t o d esign a com p r eh en sive r em ed ia t ion p a ck a ge.
T h e N RP B in d ica t e t h a t con t in u ou s exp o-su r e for 80 p er cen t occu p a n cy a t 100Bq m–3 gives a n effect ive d ose of a r ou n d 5m Sv p er yea r. In t h e m a n a gem en t of h igh r a d on levels it is essen t ia l t o r ed u ce levels a s q u ick ly a n d effect ively a s p oss ible t o t h e wor k p la ce a ct ion level. In cr ea sin g ven t ila t ion a lon e ca n r esu lt in som e clea r a dva n t a ges. In on e r oom , w it h a va lu e of 710Bq m–3d u r in g wor k in g h ou r s, m er ely op en in g w in d ow s ca u sed t h e d ose t o st a ff t o d r op fr om 5.0m Sv t o 1.1m Sv p er yea r. Im m ed ia t e a ct ion m u st b e t a k en w h en a loca -t ion is id en -t ifi ed w i-t h ver y eleva -t ed levels. In som e ca s es it is n ecess a r y t o t em p or a r ily sea l off t h e r oom , or sever ely lim it a ccess, u n t il r em ed ia t ion . In ext r em e ca ses, for say ver y sm a ll st or e r oom s, it m ay b e m or e cost effec-t ive effec-t o sea l off effec-t h e r oom p er m a n en effec-t ly a s effec-t h e cost of lon g t er m r em ed ia t ion m ay b e gr ea t er t h a n t h e va lu e of t h e sp a ce.
In som e ca ses, b efor e r em ed ia t ion , N H S st a ff w er e r eceiv in g d oses w ell a b ove 5m Sv p er yea r. T h ese d os es a r e in excess of t h ose r eceived by h os p it a l wor k er s wor k in g w it h r a d ia t ion , su ch a s r a d iogr a p h er s, r a d iolo-gist s, p h y sicist s a n d r a d iot h er a p ist s.
We h ave ca lcu la t ed t h a t ou r p r ogr a m m e cost s a r ou n d £180,000 t o a ch ieve a n a n n u a l Table III
De taile d s urve y o f an NHS building with rais e d rado n le ve ls
Location Direct reading (Bq m–3)
Reception 8 0 0
Interview room 1 ,8 0 0
Consulting room 3 ,2 0 0
Treatment room 1 ,9 0 0
Corridor 7 0 0
Staff toilets 5 0
Rest room 3 0 0
Table IV
Dis tributio n o f rado n le ve ls in s ite s in NHS pro pe rtie s in No rthampto ns hire
Average radon Hospital A Hospital B Total of
level (Bq m–3) (Northampton Sand) (Upper Lias Clay) all sites
< 100 2 0 7 1 3 0 6 5 5
101-200 3 7 4 4 1 8 4
201-300 1 3 1 9 6 4
301-400 8 7 3 9
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2 Ra ised r a d on levels a r e ver y loca lised . Som et im es on ly on e of a n a d ja cen t p a ir of r oom s is a ffect ed .
3 Ra d on gives m or e d os e t o m or e s t a ff t h a n u s e of X-r ay s a n d is ot op es for t h er a py a n d d ia gn os is.
4 T h e d os e r eceived by st a ff fr om r a d on (20-24.49m Sv – F igu r e 3) is fa r h igh er t h a n exp ect ed a n d sw ift r em ed ia l a ct ion w a s es s en t ia l.
5 For t h e t ot a l N H S s t a ff, cu r r en t r isk es t i-m a t es s u ggest t h a t r a d on in t h e wor k p la ce gives r ise t o 0.13 lu n g ca n cer s p er a n n u m (of w h ich 13 p er cen t wou ld occu r in st a ff wor k in g in a r ea s of h igh r a d on a n d s o cou ld b e avoid ed ), com p a r ed w it h a n a t -u r a l in cid en ce of s ix l-u n g ca n cer s. 6 On ce r em ed ia t ed , it is ess en t ia l t h a t n o
s t r u ct u r a l ch a n ges t a k e p la ce in bu ild in gs u n t il a n im p a ct a ssess m en t on t h e r ed u c-t ion s y s c-t em s c-t a k es p la ce.
7 P er iod ic t es t in g sh ou ld occu r t o en s u r e t h a t t h e r em ed ia t ion s y st em is s t ill effec-t ive (N a ism ieffec-t h , 1997).
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