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Particle size distribution (Granulometry)

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Reference
Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2014
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was conducted according to EU guideline, with minor deviations. Test substance is adequately characterised with its purity. However, as a single measurement was performed, intra and inter batch variation were not assessed. Therefore validity applies with restrictions.
Qualifier:
according to guideline
Guideline:
other: EUR 20268 EN: Guidance Document on the Determination of Particle Size Distribution, Fibre Length and Diameter Distribution of chemical substances (European Commission, 2002)
Deviations:
yes
Remarks:
observation with binocular; no preliminary screening test at 100 µm
GLP compliance:
no
Type of method:
Laser scattering/diffraction
Type of distribution:
volumetric distribution
Percentile:
D10
Mean:
29.4 µm
Remarks on result:
other: on sieved fraction
Percentile:
D50
Mean:
226 µm
Remarks on result:
other: on sieved fraction
Percentile:
D90
Mean:
562 µm
Remarks on result:
other: on sieved fraction
Size:
< 630 µm
Distribution:
97.4 %
Remarks on result:
other: sieved fraction
Size:
< 515 µm
Distribution:
84 %
Remarks on result:
other: corrected for fraction of total (assuming %v and %w are similar)
Size:
< 105 µm
Distribution:
27 %
Remarks on result:
other: corrected for fraction of total (assuming %v and %w are similar)
Size:
< 11 µm
Distribution:
4.2 %
Remarks on result:
other: corrected for fraction of total (assuming %v and %w are similar)
Size:
< 4.5 µm
Distribution:
1.8 %
Remarks on result:
other: corrected for fraction of total (assuming %v and %w are similar)

Pre-sieving

From a sample amount of 535.2 g, 13.8 g remained on the sieve, and 521.4 g passed through the mesh, corresponding to a passing fraction of 97.4%.

Particle size distribution

The results of the sieved sample show a half Gaussian-type distribution, the peak (ca 400 µm) being close to the upper measuring limit, and median size (x50) of 226 µm.

For the thresholds relevant to inhalation potential, results below were corrected for the total sample distribution (see above), assuming %v and %w are similar:
Inhalable fraction (< 105 µm):
         27 %
Thoracic fraction (< 11 µm):
  4.2 %

Respirable fraction (< 4.5 µm):        1.8 %
A threshold of 500 µm is generally assumed to be of concern for dust explosion potential; the corresponding corrected fraction (< 515 µm) accounts for 84%.

Conclusions:
The test substance contains a limited fraction of particles fine enough to be inhaled and reach the thoracic fraction.
Dust explosion potential should be considered.
Executive summary:

Following guidance EUR 20268 EN, the test substance was first examined under microscope, and described as crystalline sub-rounded polyhedrons, without clusters.

After pre-sieving to discard particles out of the experimental range, the particle size was then measured with a laser diffraction granulometer, in air. For the single sample tested, the distribution was Gaussian, with a median diameter of 226 µm.

With regard to inhalation potential, about 27% of total particles are smaller than 105 µm, and ca 4.2% could reach the thoracic fraction (<11 µm).

Fine particles relevant to dust explosion hazard (<515 µm) account for 84%.

Description of key information

Median diameter (D50) = 226 µm

Thoracic fraction (<11µm) = 4.2%.

Dust particles (<515µm) = 84% (dust explosion potential)

Additional information

A reliable experimental study, conducted according to a recognized EU guideline, is available. Despite restrictions due to single measurement, it is considered as a key study.