790 • Letters to the Editor
Pensis I, Luetzenkirchen F, Friede B. (2013) A method for estimating the relevant fine particle fraction in bulk materials
for classification and labelling purposes. Available at http://
annhyg.oxfordjournals.org/content/early/2014/01/02/
annhyg.met076.full.pdf. Accessed 25 February 2014.
Regulation (EC) No 1272/2008 of the European Parliament
and of the Council of 16 December 2008 on classification,
labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC,
and amending Regulation (EC) No 1907/2006. Available at
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=
OJ:L:2008:353:0001:1355:en:PDF. Accessed 25 February
2014.
SCOEL. (2003) Recommendation from the Scientific
Committee on Occupational Exposure Limits for Silica,
Crystalline (respirable dust), SCOEL/SUM/94. Available
at www.ec.europa.eu/social/BlobServlet?docId=3803&lan
gId=en. Accessed 25 February 2014.
The National Archives. (2002) The control of substances
hzardous to health regulations 2002, as amended. Available
at http://www.legislation.gov.uk/uksi/2002/2677/made.
Accessed 25 February 2014.
doi:10.1093/annhyg/meu041
Advance Access publication 16 June 2014
R E P LY
Reply to the Letters to the Editor Submitted by
T. L. Ogden and K.T. Du Clos, and by R. Foster
Regarding the Paper ‘SWeRF—A Method
for Estimating the Relevant Fine Particle
Fraction in Bulk Materials for Classification and
Labelling Purposes’
Ingeborg Pensis
Sibelco Europe MineralsPlus (Ankerpoort NV)
Op de Bos 300, NL-6223 EP Maastricht, The Netherlands
Frank Luetzenkirchen
Quarzwerke GmbH
Kaskadenweg 40, 50226 Frechen, Germany
Bernd Friede
Elkem AS
Silicon Materials
P.O. Box 8126 Vågsbygd, 4675 Kristiansand, Norway
E-mail: [email protected]
Submitted 24 January 2014; revised 9 May 2014
© The Author 2014. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.
Letters to the Editor • 791
A b st r a ct
The authors respond to the points raised in the Letters to the Editor raised by Ogden and Du Clos and by
Foster. Ad 1: The debate of the classification of respirable cyrstalline silica is outside the scope of the technical
paper. Ad 2: A standard for the determination of SWeRF is under development, in which indeed the provision
is made that for a correct determination all quartz within the fine fraction needs to be liberated. Ad 3: Dustiness
tests provide useful information for occupational hygienists, but are not suitable for fulfilling classification and
labelling requirements. Ad 4: Pipette effects are not discussed in the paper because the difference between
calculating the SWeRF from the particle size distribution and the SWeRF from sedimentation is very small.
The authors are aware of the areas of caution and the
controversial discussion concerning the classification
and labelling of the fine fraction of crystalline silica,
notably addressed by R. Foster. However, it was not
the purpose of their article to address this debate. It is
the authors’ opinion that a scientific journal like the
Annals of Occupational Hygiene is not the right platform to debate regulatory but technical issues.
The SWeRFCS method aims to measure the
fine fraction of crystalline silica in a bulk product,
regardless of the substance’s hazard classification.
Currently, the SWeRF method has been validated
to meet the generic cut-off values of 1% which corresponds to a classification of the crystalline silica
fine fraction as STOT RE 1. Whether the SWeRF
method also allows reliable quantification of the
fine fraction at a generic cut-off value of 0.1% cannot be answered yet and will be subject of future
experimental work.
The STOT RE 1/2 classification is indeed not the
only one submitted to the classification and labelling inventory of the European Chemicals Agency;
it is however the one notified by the majority (690
STOT RE 1, 998 STOT RE 2, 180 Carcinogenic 1A,
and 460 ‘not classified’ notifications for Quartz CAS
14808-60-7, EC number 238-878-4). The SWeRF
method provides the EU suppliers who implement the STOT RE 1/2 classification with a tool to
quantify the fine fraction of crystalline silica in their
bulk products, for the purpose of their products’
classification.
Regarding point 2 of Ogden and Du Clos, it is
indeed correct that when a mineral is denser than
quartz and not all quartz is separated from this mineral, the SWeRF content will be underestimated.
When the density is lower, the SWeRF will be overestimated. We are developing a standard for the determination of SWeRF, in which indeed the provision is
made that for a correct determination all quartz within
the fine fraction needs to be liberated.
The authors agree with the statement of Ogden
and Du Clos in their third point that dustiness tests
and the SWeRF sedimentation test are both dispersing techniques for particles used for hazard assessment. Dustiness tests in accordance with EN 15051
(CEN, 2006), however, do not quantify the amount
of the relevant fine fraction in the bulk material, what
is actually required by the European Regulation on
Classification, Labelling and Packaging of substances
and mixtures and the UN Globally Harmonized
System of Classification and Labelling of Chemicals
(United Nations, 2011), but they quantify the amount
of the inhalable, thoracic, and respirable fraction that
is generated upon agitation of the bulk material. This
gives very useful information for occupational hygienists, too, but does not enable fulfilling classification
and labelling requirements. Furthermore, studies have
shown that the results of dustiness tests depend on
the method applied, i.e. continuous drop method vs.
rotating drum method (Lidén, 2006).
There is an essential difference between how much
fine material actually is present in the bulk material
and how much of the fine particles will be released
upon agitation. Agitation (either rotating drum or
continuous drop) can both lead to underestimation of
the fine fraction due to agglomeration which again is
influenced by humidity and overestimation when fine
particles are formed in situ.
The authors did not claim that sedimentation is an
endpoint under GHS and CLP. Sedimentation is one
of two possibilities to quantify the relevant fine particle fraction in a bulk material for classification and
labelling purposes.
The authors acknowledge the findings of Ogden and
Du Clos in point 4 regarding their studies of fluid flow
from a cylinder into a pipette, which has relevance to the
792 • Letters to the Editor
sedimentation method as presented in the SWeRF article (Pensis et al., 2014). The part of the fluid below the
level of the pipette is always higher in density. When separation is not perfect this can only increase the SWeRF.
This effect was not exactly quantified but according to
the experimental results as presented in the paper, the
difference between the SWeRF calculated from the particle size distribution and the SWeRF determined by
sedimentation on pure substances, i.e. quartz flour, was
relatively small. Since the error is always on the safe side,
it was decided not to discuss this in the article.
A c k n o w l e d g e m e n ts
The authors wish to thank the authors of the Letters to
the Editor for their comments.
References
CEN. (2006) EN 15051, Workplace atmospheres. Measurement
of the dustiness of bulk materials. Requirements and reference test methods. Brussels, Belgium: European Committee
for Standardisation.
Lidén G. (2006) Dustiness testing of materials handled at
workplaces. Ann Occup Hyg; 50: 437–9.
Pensis I, Luetzenkirchen F, Friede B. (2014) SWeRF–a method
for estimating the relevant fine particle fraction in bulk
materials for classification and labelling purposes. Ann
Occup Hyg; 58: 501–11.
United Nations. (2011) Globally Harmonized System of
Classification and Labelling of Chemicals (GHS). 4th
edn. New York and Geneva. ISBN no. 978-92-1-117042-9.
Available at http://www.unece.org/fileadmin/DAM/trans/
danger/publi/ghs/ghs_rev04/English/ST-SG-AC10-30Rev4e.pdf. Accessed 22 January 2014.