SWeRF Size-Weighted Respirable Fraction Size-Weighted Respirable - - PowerPoint PPT Presentation

SWeRF Size-Weighted Respirable Fraction Size-Weighted Respirable Fraction in bulk products A summary

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Why SWeRF?

SWeRF was introduced to answer:

• what is the amount of the respirable particles in a given

material?

• what is the amount of the respirable crystalline silica in a

given material? It is necessary to provide an answer to this question for classification and labelling as it is intended to notify the f f C g y respirable fraction of crystalline silica in the ECHA inventory The method should be easy-to-use in companies’ labs.

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Respirable particles D fi iti Definition A respirable particle is a A respirable particle is a particle that can penetrate deep into the lungs and deep into the lungs and reach the alveoli.

But, not all respirable particles behave the same.

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Respirable particles

Smaller particles have a higher probability to enter the alveoli. According to European standard EN 481: Particle size (Aerodynamic) Probability (%)

Not physical

(Aerodynamic) 1 m 97.1 5 m 30

diameter

5 m 30 10 m 1.3 16 m

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How to define the respirable fraction?

The respirable fraction consists of : All particles smaller than:

• 5 microns?

5 microns?

• 10 microns?
• 12 microns?

12 microns?

• 16 microns?

How do you choose it? How do you choose it? To decide a cut off is arbitrary and not scientific To decide a cut off is arbitrary and not scientific.

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SWeRF

SWeRF can be used to determine the respirable i f ti i b lk t i l b i th size fraction in a bulk material by using the probability distribution of EN 481.

Probabilit y dist ribut ion 100 Particle size Probability (%) 1 m 97.1 60 70 80 90 EN 481 1 m 97.1 5 m 30 10 m 1.3 16 m 20 30 40 50 60

%

 10 20 1 10 100 µm

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Size Weighted Respirable particles

SWeRF uses the probability distribution of EN 481 to calculate the amount of respirable size fraction.

– 97.1 % of the amount of particles of 1 m are taken into account. 97.1 % of the amount of particles of 1 m are taken into account. – 30 % of the amount of particles of 5 m are taken into account. – Etc..

Size weighted

Size dist ribut ion

Size weighted

Size dist ribut ion

30 35 40

Tot al SWeRF

20 25 30 10 15

“Small particles have more

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1 10 100 1000

influence than large particles”

7 1 10 100 1000

µm

SWeRF of crystalline silica

The next step is to determine the amount of respirable t lli ili crystalline silica: SWeRFcs In Quartz flour or other crystalline silica polymorphs, this is easy: easy: SWeRF = SWeRFcs In other materials there are two approaches: C l l ti

• Calculation
• Sedimentation

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SWeRFcs Calculation Calculation

To determine SWeRFcs: Th SW RF i l l t d i th i di t ib ti f th The SWeRF is calculated using the size distribution of the

• material. This is then multiplied with the crystalline silica content
• f the bulk:

SWeRFcs = SWeRF x CS

cs

This is correct if the PSD of both material and crystalline silica is h the same. When the difference in PSD becomes too important another approach is necessary approach is necessary. Link to calculation sheet.

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SWeRFcs Sedimentation

For this approach the size weighted respirable fraction is For this approach the size weighted respirable fraction is separated using sedimentation. A sample is suspended in a liquid and left to settle Larger A sample is suspended in a liquid and left to settle. Larger particles will sediment faster leaving the smaller particles in

• suspension. At a given time the sedimentation in liquid is

equal to the separation according to EN 481. At that time, the particles in suspension represent the SWeRF. SWeRFcs is determined by determining the CS content of this separated fraction by XRD, IR or other methods.

Link to sedimentation sheet.

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SWeRFcs Calculation vs Sedimentation

Calculation of SWeRFcs is easiest method. It uses a size distribution and the CS content. However this will in most cases result in an overestimation because CS normally tends to be coarser than the rest of the material. This is f ‘ f specially the case for ‘softer’ materials. Determination by sedimentation needs more preparation Determination by sedimentation needs more preparation since the right fluid for sedimentation needs to be chosen to avoid agglomeration. The particles need to ‘behave’ (e.g. gg p ( g not flocculate) as they would in air. Sedimentation of materials with coarse particles needs more investigation.

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IMA Metrology WG Project

Validity of the SWeRF calculation method

Samples tested: 3 quartz flours 1 sand 1 barite with addition of quartz

Validity of the SWeRF calculation method checked by method of sedimentation

Samples tested: 3 quartz flours, 1 sand, 1 barite with addition of quartz, 1 feldspar, 1 limestone, 1 leucophyllite, 1 clay, 1 diatomaceous earth calcined R lt Results: Quartz showed a good correlation between the calculated SWeRFcs and the SWeRFcs determined by sedimentation as well as barite with addition of quartz. During the separation by sedimentation most minerals showed agglomeration During the separation by sedimentation, most minerals showed agglomeration which makes it impossible to check the validity of the calculated SWeRFcs

• f these minerals.

Conclusion: Since the method works for quartz and for minerals to which quartz was added, it is possible that the calculation of SWeRF is a valid method for other minerals it is possible that the calculation of SWeRFcs is a valid method for other minerals. However this should be validated per mineral by experiments during which agglomeration is prevented.

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Important considerations

SWeRF

• Mineral properties such as:

p p Density, porosity, particle shape, agglomeration.

• SWeRF is only usable for ultra fine particles when a convention for

these particles is available. (EN 481 is not applicable for these particles.) these particles is available. (EN 481 is not applicable for these particles.) Calculated SWeRF Different Particle Size Distribution (PSD) techniques give different results Different Particle Size Distribution (PSD) techniques give different results Calculated SWeRFcs When the difference in PSD between the material and the CS becomes too important another approach is necessary. Sedimentation SWeRF The right fluid for sedimentation needs to be chosen to avoid agglomeration or particle disintegration.

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IMA Metrology WG Recommendations

• For quartz flours and sand, the calculation method can be applied

F i l h l l i h d i i d h

Recommendations

• For some minerals the calculation method is not appropriate and they

have to determine the SWeRF and SWeRFcs by sedimentation F th di t ti th d i ti ti i d d P

• For the sedimentation method, more investigation is needed. Per

mineral a suitable liquid or dispersant agent needs to be selected. B f th l l ti th d i d th lidit h ld b h k d b

• Before the calculation method is used the validity should be checked by

the sedimentation technique per mineral. IMA project or each company or section’s decision? p j p y The Metrology WG considers that the SWeRF is a valid method The Metrology WG considers that the SWeRF is a valid method -

• provided

provided h i l k th i t d dj t t h i l k th i t d dj t t d each mineral makes the necessary experiments and adjustments each mineral makes the necessary experiments and adjustments -

• and

and they recommend a standardisation of the method through CEN they recommend a standardisation of the method through CEN

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CEN Standardisation

Preliminary contacts already made with the CEN They would welcome a new work item They would welcome a new work item To fasten the process, a special procedure could be introduced = PQ procedure: 20 months instead of 4 years

• 1. A document meeting the format and content requirements of a CEN standard

is submitted for admission (2 months) f C G G f

• 2. The draft standard is discussed within an existing CEN WG -- e.g. WG 3 of

TC 137 (13 months)

• 3. The standard is sent for formal vote and publication as a EN standard in all

EU languages (5 months) No financial support required by industry CEN is waiting for our proposal

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Questions?

If after this meeting you still have some questions you can contact me at the q y following E-mail address: i pensis@ankerpoort com i.pensis@ankerpoort.com

Reserve slides Reserve slides

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Respirable CS or CS Dust

IARC classified CS dust Target organ is lung more specific alveoli Only respirable fraction can reach the alveoli Conclusion: CS Respirable is appropriate p pp p Classification & Labelling should address the respirable g p fraction of crystalline silica How to define it?

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SWeRF versus Dustiness SWeRF versus Dustiness

Dustiness and SWeRF should not be confused Dustiness and SWeRF should not be confused. Both are valid methods but give answers to different questions: questions:

• Dustiness determines the amount that comes out.

S

• SWeRF determines what is in a sample

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