Radon—A regional electricity company approach to assessment and control

Ann. orcup. Hyy , Vol. 39. No. 2, pp. 203-210, 1995 Elsevier Science Ltd CI 1995 British Occupatmnal Hygiene Society Printed in Great Britain. All rights reserved ooO34878/95 $9.5O+O.Ml

Pergamon

Copyright

0003-4878(94)00111-1

RADON-A REGIONAL ELECTRICITY COMPANY ,APPROACH TO ASSESSMENT AND CONTROL D. L. Evans South Western Electricity

plc, Trevenson Lane, Pool, Redruth, Cornwall (Received in jnal,form

TRl5 3RF, U.K.

5 September 1994)

Abstract-There are statutory limits on exposure to radon in workplaces in the United Kingdom [Health and Safety, The Ionizing Radiation Regulations, Statutory Instrument 1333. HMSO, London (1985)]. South Western Electricity plc (SWEB) employs approximately 5500 staff within the group in the area which stretches from the Isles of Stilly to Bristol and across into South Wales and Southern England (where it has retail outlets) in parts of which high concentrations of radon can be expected [Radiation doses-maps and magnitudes. NRPB, Didcot (1985)]. The Company’s method of assessment and details of a successful remediation scheme installed in a large modern office are described.

NOMENCLATURE becquerel (Bqtthe SI unit of radioactivity equal to one disintegration sievert (Svta radiation equivalent dose

per second (1 dps)

Working level (WLkthe special unit of potential alpha energy concentration in air and is any combination of short-lived daughters of radon-222 in unit volume of air such that total potential alpha energy concentration for complete decay to lead-210 is 2.08 x 10m5 J mm3 [HMSO, 1985, part 1,2(1)1 Exposure to radon daughters is expressed in units of working level month (WLM) (part 3, Section 9)] WLxh Exposure (WLM) = 170,

where h=exposure

time (h) [HMSO,

[HMSO,

1985

1985 (part 3, Section 9)]

4.8 WLM gives rise to a committed equivalent dose equated to 50 mSV [HMSO, 1985 (part 3. Section 9)] Action level--concentration of radon above which remedial measures should be introduced Occupational action level =400 Bq m-3 =0.03 WL (Gooding and Dixon, undated) General public (homes) action level =200 Bq mm3 (NRPB, 1990) Annual dose limit for workers not classified as radiation workers = 5 mSv year- ’ (NRPB, 1990) Annual dose limit for general public-l mSv year-’ (NRPB, 1985)

INTRODUCTION

South Western Electricity plc is the Regional Electricity Company for a region which stretches from the Isles of Stilly and up through the counties of Cornwall, Devon, Somerset and Avon. It also covers a tiny area of Dorset, and the electrical appliance retail subsidiary, SRL, has outlets in South Wales, Wiltshire and Hampshire. The group as a whole employs approximately 5500 staff involved not only in engineeringengineers, linesmen, jointers, electricians-but in transport, telecommunications, computing, administration, personnel and retailing, and specialist units such as diving and helicopters. 203

D. L. Evans

204

Th

At

Bi Pb

Fig. 1. Principal decay scheme of 238U.

Radon-222 is an inert (noble) gas (in fact the only gas) in the decay scheme of uranium-238 shown in Fig. 1. It has 56 MeV energy-alpha particles and a half-life of 3.8 days. The damaging daughter products (polonium, lead and bismuth) have halflives of lessthan 30 min. The hazard is an increased risk of lung cancer with estimated lifetime risks shown in Table 1. Table 1. Increased risk of contracting Radon concentration (W m-7 20 100 200* 400t

Non-smokers Smokers (number in 1000)

Total population

10

1

3

50 loo 200

5 10 20

15

*Action level for homes. tAction level for workplaces (Source: NRPB.)

In the U.K. controls evolved as follows: -1974 -1975 -1977 -1980 -1982

lung cancer

Health and Safety at Work, etc., Act; Voluntary Control; ICRP 26; EC Directive; ICRP 32;

30 60

Radon-a

regional electricity

205

company approach

-1985 The Ionizing Radiation Regulations (SI 1985 No. 1333); -1990 ICRP 60. Enforcement is by the Health and Safety Executive and Local Authorities (Environmental Health Departments). The National Radiological Protection Board (NRPB) invited the Company to participate in a central government funded exercise which was aimed at assessing workplaces in Devon and Cornwall (Dixon, 1989). The NRPB is an independent statutory body set up by the Radiological Protection Act 1970.

INVESTIGATION

AND

RECOMMENDATIONS

Following advice from Dr Daryl Dixon of the NRPB, 13 track-etch monitors were placed in the Company’s Office at Pool-situated between Camborne and Redruth. The office is on two floors, each of approximately 2000 m2. About 180 staff are employed. The detectors are of hemispherical yellow plastic, approximately 60 mm dia., containing rectangular strips of CR-39-a sensitive nuclear track recording plastic. These were left in situ for 1 month to obtain average concentrations and then returned to the NRPB for analysis. Average concentrations are used since the level of radon fluctuates throughout the day and season(seeFigs 2 and 3). The analysis process consists essentially of etching the recording plastic in a caustic solution (sodium hydroxide), which attacks preferentially the sites of alpha-particle damage. Each imperfection then shows up under a microscope as a small spot. Counting the spots gives a reliable indication of the average radon level to which the strip has been exposed.

0

I 2

4 4

I 6

I 8

, 10

Time

Fig. 2. Radon variation

I 12

I

I

I

I

I

I

14

16

18

20

22

24

so”rcs: NRPB

of day

throughout

the day.

206

D. L. Evans

J

F

m

A

m

J

J

A

S

Month

Fig. 3. Radon variation

0

N

0 source: NRPB

from season to season.

The results of our initial survey were interesting but before referring to them a very brief reference to the units may be helpful. A radon daughter concentration of 0.03 WL (working level) is deemed to give an effectiveequivalent dose of 5 mSv year- 1 (milli-sieverts per year) (Gooding and Dixon, undated). The 0.03 WL can be equated to 400 Bq m -3 (Becquerels per cubic metre) (Gooding and Dixon, undated) the action level for workplaces. If the annual dose is above the 5 mSv year-’ there are two options: (1) arrange radiological surveillance [HMSO, 1985 (part 3, Section S)]; or (2) establish remedial measures to avoid the need for compliance [HMSO, 1985 (part 3, Section 6)]. SWEB chose the secondoption owing to the difficulties of staff in an office environment having to wear personal radiation detectors together with the need to involve actively our Radiation Protection Adviser, to carry out routine monitoring, to keep records, to establish local rules and to provide information and training. Focusing then on the action level in workplaces of 400 Bq rne3, the results of our initial survey in the Cornwall Office can be seenin Table 2. The ‘no result’ could be attributed to a faulty detector, as subsequent results indicated the presenceof radon222 concentrations in this area. Clearly a problem existed and the following actions were taken: (1) a further set of monitors was installed to obtain confirmation; (2) the Company’s Radiation Protection Adviser (RPA) (Mr K. Foy, Hygienist at the Electricity Association, London) was informed, and his assistance is gratefully acknowledged; and (3) an approach was made to Cornwall County Council (CCC) for advice on remediation. Mr Trevor Gregory of CCC had been working for some time in conjunction with

Radon-a

regional electricity company approach

Table 2. SWEB Cornwall Location

office-initial

survey

Concentration

Conference room Restaurant Switchroom (well) Switchroom Service riser (west) Service riser (east) Control room Computer room Telecommunications Typists Personnel Information systems Reception

207

(Bq m-3)

200 320 71so* No result 540* 160 90 330 430s 530* 560* 520* 450*

*Action level exceeded (seven locations out of 13).

the NRPB, since the Council has responsibility for educational establishments in addition to other premises. We are very grateful for the assistanceand advice given. In the meantime, the data from our second set of monitors had been analysed and the results received. The results are shown in Table 3 with the previous results alongside for comparison. Table 3. SWEB Cornwall office-initial confirmatory results

survey and

Concentration 1

Location Conference room Restaurant Switchroom (well) Switchroom Service riser (west) Service riser (east) Control room Computer room Telecommunications room Typists Personnel Information systems Reception

200 320 7180 No result 540 160 90 330 430 530 560 520 450

(Bq rnm3) 2 360 420* 4050* 5020* 480* 250 110 260 560* 520* 460* 490* 420*

*Action level exceeded (nine times out of 13).

REMEDIAL

MEASURES

The Company’s Design Services Manager was informed and his department produced proposals for mitigation. The plan was to install 18 sumps to act as reservoirs for the gas. The sumps to be connected to ducts and fans to extract, expel and disperse and, therefore, dilute the gas away from the building. The sumps are areas of negative pressure into which the gas is attracted.

D. L. Evans

208

One of the difficulties was how to carry out the civil and electrical work whilst allowing normal office work to continue. Since this was our first mitigation schemeit was decided that it would be preferable to over-design rather than have too have ;I second attempt and causedouble disruption. Drilling was carried out outside normal working hours. It was also recognized that it would be unrealistic to attempt to adhere rigidly to the CCC norm of one sump per 250 m2 (Cornwall County Council, undated). However. the average area of influence per sump is approximately 110 m*. Three of the sumps were constructed internally through the building’s concrete raft. The remainder were excavated along the perimeter from outside the building after breaking through the outer wall beneath the raft. The internal sumps were constructed of block/brick to CCC design (Cornwall County Council, undated) as shown in Fig. 4, but the outer perimeter ones, for practical reasons, were of wire mesh surrounded by polythene sheet. Boxes were made to house the fans and discrete outlets made for exhaust and dispersion away from the influence of the building’s air intake system.

600 x 900 P.C.Paving Slab 3 CoursesEngineerins B dw 75 mm OpenPm-pen 150 dia Plastic Pipe dw WeldedAir-tight Joints 600 x 900 P.C.Paving Slab with clean broken brick or stone

i Fig. 4. Radon sump for underfloor

construction

(Cornwall

C. C. design).

Whilst the remediation schemecivil and electrical work was progressing, another set of monitors was installed to give immediate pre-remediation results. Table 4 lists the results with earlier values alongside for comparison. After the scheme had been commissioned and in operation for approximately 6 weeks, another set of monitors was installed. The results were impressive (see Table 5).

Radon-a

regional electricity

Table 4. SWEB Cornwall

company approach

office-initial, confirmatory results

Location

1

Conference room Restaurant Switchroom (well) Switchroom Service riser (west) Service riser (east) Control room Computer room Telecommunications room Typists Personnel Information systems Reception

209

and pre-remediation

Concentration (Bq m-3) 2

320 7180* No result 540* 160 90 330 430* 530* 560* 520* 450*

360 420* 4050* 5020* 480* 250 110 260 560* 520* 460* 490* 420*

3

380 600* 9080* 5360* 610* 140 200 500* 1030* 460* 690* 570* 430*

*Action level exceeded.

Table 5. SWEB Cornwall

office-results 1

Location Conference room Restaurant Switchroom (well) Switchroom Service riser (west) Service riser (east) Control room Computer room Telecommunications room Typists Personnel Information systems Reception

before and after remediation Concentration 2

200 320 7180 No result 540 160 90 330 430 530 560 520 450

360 420 4050 5020 480 250 110 260 560 520 460 490 420

(Bq me3) 3 380 600 9080 5360 610 140 200 500 1030 460 690 510 430

4 60 50 50 40 30 70 <30 130 <30 50 50 50 40

Subsequent tests have proved to be equally satisfactory and will be repeated annually. The extraction system is regularly monitored and records kept. FUTURE

INSPECTION

PROGRAMME

Clearly each employer has a duty to assesshis own risks in the context of radon as well as for any other hazard. SWEB now has a policy requiring the assessmentof all appropriate workplaces and a radon information leaflet has been issued to staff. Approximately 180premiseswere identified as needing assessment.With the assistance of the NRPB these were listed in order of priority based upon post codes. Three levels were established. Level l-premises in areas of expected highest radon concentration have now been assessed.Following advice from the NRPB, detectors are now left in place for

210

D. L. Evans

3 months. This allows rolling, year-round, assessments whereas a monthly test during the summer period would not be representative-since the weather would be warmer and, therefore, there would be greater ventilation in use diluting the radon concentration. Level 2-areas of next highest expected radon concentrations. Level 3-areas of least expected radon concentrations. The Company also has a NITON RAD 7 instrument (Vertec Scientific, Reading RG7 4QW, U.K.) which can be used to reinforce the track-etch system the output being compatible with the NRPB track-etch detectors. This produces a chart or the information can be downloaded to a PC. REFERENCES Cornwall County Council (Undated) Radon exclusion, Standard Advice Notes (existing premises). Architect’s Department, County Hall, Truro TRl 3AX, U.K. Dixon, D. W. (1989) Survey of radon in workplaces, Circular No. 6. National Radiological Protection Board (NRPB), Didcot, U.K. Gooding, T. D. and Dixon, D. W. (Undated) Radon in U.K. workplaces, measurements. National Radiological Protection Board (NRPB), Didcot, U.K. HMSO (1985).Health and Safety, the Ionising Radiation Regulations. Statutory Instrument 1333.HMSO, London. NRPB (1985) Radiation doses-maps and magnitudes. National Radiological Protection Board (NRPB), Didcot, U.K. NRPB (1990)Limitation of human exposure to radon in homes. Statement by the NRPB, Documents of the NRPB.