7/28/2019 775.full.pdf

http://slidepdf.com/reader/full/775fullpdf 1/3

 Ann. Occup. Hyg., Vol. 53, No. 8, pp. 775–777, 2009

Ó The Author 2009. Published by Oxford University Press

on behalf of the British Occupational Hygiene Society

doi:10.1093/annhyg/mep072

Editorial

Proposed British–Dutch Guidance on MeasuringCompliance with Occupational Exposure LimitsT. L. OGDEN*

Co-chair for British Occupational Hygiene Society (BOHS), BOHS–NVvA Working Party on

Compliance Testing, Melbourne Court, Millennium Way, Derby DE24 8LZ, UK 

Received 15 September 2009; in final form 15 September 2009; published online 3 November 2009

Occupational exposure limits (OELs) for hazardoussubstances are usually defined as exposures averaged

over 8 h or 15 min which must not be exceeded. In

the European Union (EU), examples are the limits

in the Chemical Agents Directive (EU, 1998) and

the Carcinogens Directive (EU, 2004). But if we

define the limits as exposures which must never be

exceeded, we disregard the complex patterns of real

exposure. It is common experience that exposure

distributions often include results which are several

times the median value, not because of a failure of 

control but because there is a statistical chance that

the many factors which determine exposure combinein a way which produces an outlying result. Do these

outliers constitute non-compliance or are they freak 

happenings which can be disregarded, and if so what

is the criterion for distinguishing ‘freak’ measure-

ments from significant results which must be taken

into account?

This has been a problem ever since OELs moved

from being ‘guidelines to be used by professional in-

dustrial hygienists’ (ACGIH, 2009) to being sharp

cutoffs of legally allowable exposure, and many

attempts have been made to write guidance on how

to demonstrate compliance with the limits. Probably,the most famous is of Leidel et al. (1977), published

by the US National Institute of Occupational Safety

and Health (NIOSH). In a commentary last year,

Ramachandran (2008) described this guidance and

its limitations and NIOSH’s plans to revise it. This

work continues. In Europe, the most prominent guid-

ance is the European Standard EN689 (CEN, 1995).

A couple of years before that was published, the

British Occupational Hygiene Society (BOHS) had

produced a Technical Guide on the problem (BOHS,

1993). These documents all try to deal with theunderlying difficulty that an OEL defined as a sharp

threshold is out of step with the laws of physics that

determine how exposure varies in the workplace.

A second problem is that individuals apparently

doing the same job in the same way can differ sub-

stantially in exposure, which is not fully taken into

account in EN689 and the earlier documents. The

two problems of variability from shift to shift and

from worker to worker mean that a statistically valid

test of compliance with the OEL requires far more

measurements than would normally be considered

practicable.Two years ago, a joint Working Party on the prob-

lem was appointed by the BOHS and Nederlandse

Vereniging voor Arbeidshygiene, the Dutch Occupa-

tional Hygiene Society (NVvA). This has produced

draft guidance which is open for comment on the

societies’ websites until the end of 2009 (http:// 

www.bohs.org and http://www.arbeidshygiene.nl/ 

index.php). The guidance is not finished, but the

Working Party felt that it would be useful to expose

it to public comment at this stage. Its approach to

the fundamental problem is to emphasize the impor-

tance of the principles and methods of control, not just compliance with OELs. In this, it follows the

European Chemical Agents Directive (EU, 1998),

which in Articles 5 and 6 requires application of 

good control practice alongside but independently

of compliance with exposure limits. This dual ap-

proach is also emphasized in the British COSHH

regulations (HSE, 2005).

However, when it comes to measuring compliance,

the statistical problem has to be faced. Like most

other guidance, the British–Dutch draft uses a crite-

rion that 95% of exposures should be below the

OEL, arguing that this represents good professional

practice even if it does not strictly guarantee compli-

ance with the law. The main test involves division of 

*Author to whom correspondence should be addressed.Tel: þ44-1332-298101; fax: þ44-1332-298099; e-mail:editor@ogs.org.uk 

775

  b  y g u e  s  t   onM

 a  y 3  0  ,2 

 0 1 

 3 

h  t   t   p :  /   /   a nnh 

 y g . oxf   or  d 

 j   o ur n

 a l   s 

 . or  g /  

D o wnl   o a  d 

 e  d f  r  om

7/28/2019 775.full.pdf

http://slidepdf.com/reader/full/775fullpdf 2/3

the workforce into similarly exposed groups (SEGs)

and measurement to determine the between-shift and

between-worker variances. These are then combined

to estimate two measures of compliance.

(1) Group exceedance. The probability that the

time-weighted average exposure from a random

worker in the SEG exceeds the OEL.(2) Individual exceedance. The proportion of all

the workers in the SEG who have 95th percen-

tiles of exposure exceeding the OEL.

The parameters therefore recognize the differences

between exposures of workers nominally doing the

same job. In practice, the second parameter more

often indicates non-compliance than the first, but

having both provides a pointer to whether better con-

trol should be applied to the whole group or whether

it should be concentrated on individuals.

There is a software package SPEED obtainablefrom a University of Utrecht website http://www.

iras.uu.nl/iras_speed.php which is currently being

updated to provide easy calculation of the parame-

ters. The Working Party’s draft also gives an illus-

trated description of their calculation using

Microsoft Excel.

The recommended method inevitably includes

a lot of measurement. However, the guidance also

gives a Stage 1 screening process, requiring only

three measurements, designed to pick SEGs that have

high probability of non-compliance, for which it

would be sensible to apply better control before im-plementing the full compliance test. The guidance

also discusses three shortcuts, which require a lot less

sampling, but which have various shortcomings.

The guidance and its methods make extensive use

of various sources. The American Industrial Hygiene

Association software IHSTAT (http://www.aiha.org/ 

content/insideaiha/volunteerþgroups/eascomm.htm)

is often referred to. The Stage 1 test is based on an

evaluation of various strategies by Hewett (2005)

and published on his company’s website. Among

other sources, the calculation methods use Rappaport

and Kupper’s (2008) book, an exposition of the prob-lems which is systematic and clear and well illus-

trated from workplace data, although it does not

shy away from the inevitable mathematics. In my

view, it is indispensable for anyone seriously inter-

ested in these problems. Rappaport and Kupper evi-

dently have little sympathy for the feeling that

hygienists can only be expected to take a few meas-

urements, and they refer to the potential of, for exam-

ple, self-assessment. The Working Party’s main test

is also strongly influenced by Kromhout et al.’s

(2005) chapter.

Producing an international document on sucha complex subject is clearly difficult, and the draft

as it stands is really the work of the British half of 

the Working Party, strengthened by comments from

their Dutch colleagues. The Working Party intends

that any British bias should be corrected in the

coming months as a result of the consultation. Every-

one agrees that an international approach is highly

desirable, particularly for countries in the EU or

influenced by it. There is currently a group in

Norway working on the same task, and we hope thatthe work can be integrated with theirs and possibly

with others elsewhere in Europe. The work on the

NIOSH method has already been mentioned, and

Ramachandran (2008) explains the consultation with

stakeholders involved in that.

It is perhaps unrealistic to expect that there will

ever be a single method because over the last 30 years

research has repeatedly shown shortcomings of past

methods and possibilities of new approaches, and

there is no sign of this stopping. At the moment,

for example, there is a lot of attention to Bayesian

methods in exposure assessment. The British–Dutchgroup did not feel that the Bayesian approach had

reached a stage where it could be incorporated into

their main method, but clearly things are developing

fast, and perhaps we need to think in terms of guid-

ance that is revised every 2 of 3 years so it remains

a statement of current good practice rather than a doc-

ument fixed for a long time.

For the moment, however, the British–Dutch

Working Party hopes that the consultation will lead

to useful comments and fairly fast revision to a ver-

sion that can be published online with the imprimatur

of the two societies.

REFERENCES

ACGIH. (2009) 2009 TLVs and BEIs. Cincinnati, OH: ACGIH.British Occupational Hygiene Society. (1993) Sampling

strategies for airborne contaminants in the workplace.Technical Guide No. 11. Leeds, UK: H&H ScientificConsultants.

CEN. (1995) European Standard EN689:1995. Workplaceatmospheres—guidance for the assessment of exposure byinhalation to chemical agents for comparison with limitvalues and measurement strategy. Brussels, Belgium: Com-ite Europeen de Normalisation.

European Union. (1998) Council Directive 98/24/EC of 7 April1998 on the protection of the health and safety of workersfrom the risks related to chemical agents at work. Available(in English) at http://eur-lex.europa.eu/smartapi/cgi/ sga_doc?smartapi!celexplus!prod!DocNumber&lg5en&ty-pe_doc5Directive&an_doc51998&nu_doc524. Accessed11 September 2009.

European Union. (2004) Directive 2004/37/EC of the EuropeanParliament and of the Council of 29 April 2004 on theprotection of workers from the risks related to exposure tocarcinogens or mutagens at work. Available (in English)at http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32004L0037R(01):EN:HTML. Accessed 11September 2009.

Hewett P. (2005) Performance-based exposure assessment

strategies for TWA exposure limits. Technical Report No.05-03. Morgantown, WV: Exposure Assessment SolutionsInc. Available at http://www.oesh.com/downloads/ 

776 T. L. Ogden

  b  y g u e  s  t   onM

 a  y 3  0  ,2 

 0 1 

 3 

h  t   t   p :  /   /   a nnh 

 y g . oxf   or  d 

 j   o ur n

 a l   s 

 . or  g /  

D o wnl   o a  d 

 e  d f  r  om

7/28/2019 775.full.pdf

http://slidepdf.com/reader/full/775fullpdf 3/3

TR%2005-03%20PBEAS%20Design.pdf. Accessed 7August 2008.

HSE. (2005) Control of substances hazardous to health. 5th edn.Approved Code of Practice and Guidance. London: Healthand Safety Executive.

Kromhout H, van Tongeren M, Burstyn I. (2005) Design of exposure measurement surveys and their statistical analyses.In: Gardiner K and Harrington JM, editors. Chapter 3 of oc-cupational hygiene. 3rd edn. Oxford: Blackwell Publishing.

Leidel NA, Busch KA, Lynch JR. (1977) Occupationalexposure sampling strategy manual. Cincinnati, OH:National Institute for Occupational Safety and Health.

Ramachandran G. (2008) Toward better exposure assessmentstrategies—the new NIOSH initiative. Ann Occup Hyg;52: 297–301.

Rappaport SM, Kupper LL. (2008) Quantitative exposure as-sessment. El Cerrito, CA: Stephen Rappaport ISBN: 978-0-9802428-0-5.

British–Dutch Guidance on Measuring Compliance with OELs 777

  b  y g u e  s  t   onM

 a  y 3  0  ,2 

 0 1 

 3 

h  t   t   p :  /   /   a nnh 

 y g . oxf   or  d 

 j   o ur n

 a l   s 

 . or  g /  

D o wnl   o a  d 

 e  d f  r  om