Development of handling energy factors for use of dustiness data in exposure assessment modelling

Abstract Several exposure assessment models use dustiness as an input parameter for scaling or estimating exposure during powder handling. Use of different dustiness methods will result in considerable differences in the dustiness values as they are based on different emission generation principles. EN17199:2019 offers 4 different dustiness test methods considering different dust release scenarios (e.g. powder pouring, mixing and gentle agitation, and vibration). Conceptually, the dustiness value by a given method can be multiplied with a scenario-specific modifier, called a handling energy factor (Hi), that allows conversion of a dustiness value to a release constant. Therefore, a Hi, scaling the effective mechanical energy in the process to the energy supplied in the specific dustiness test, needs to be applied. To improve the accuracy in predictive exposure modelling, we derived experimental Hi to be used in exposure algorithms considering both the mass- and number-based dust release fraction determined by the EN17199-3 continuous drop (CD) and the EN17199-4 small rotating drum (SRD) test methods. Three materials were used to evaluate the relationship between dustiness and dust levels during pouring powder from different heights in a controlled environment. The results showed increasing scatter and difference between the Hi derived for the 2 test methods with increasing pouring height. Nearly all the Hi values obtained for both SRD and CD were <1 indicating that the dustiness tests involved more energy input than the simulated pouring activity and consequently de-agglomeration and dust generation were higher. This effect was most pronounced in CD method showing that SRD mechanistically resembles more closely the powder pouring.


Annex I. Evaluation of dustiness parameters
The respirable dustiness mass fraction (in mg kg -1 ) from SRD was determined according to the equation below, following the procedures given in EN 17199-4:2019: where QA and QB1 are the air volume flows through the SRD and cyclone, respectively (in L min -1 ), mf is the blank-filter corrected mass of dust collected on the cyclone filter (in mg) and m is the mass of powder used in the test in kg.
For CD, the respirable ( − ) and inhalable  ,ℎ− dustiness mass fractions were determined according to the following equations (EN 15051-3: 2013) where ∆  is the mass of the dust collected by the sampler for respirable dust (in mg), ∆  is the mass of the dust collected by the sampler for inhalable dust (in mg),   is the drop mass in the collector tank (in kg),   is the flow rate of the sampler for respirable dust (in L min -1 ),   is the flow rate of the sampler for inhalable dust (in L min -1 ),   is the total flow rate (in L min -1 ) and   =   +   +   (  is the main pump flow rate (in L min -1 ).
Additionally, the number-based dustiness index DIN (mg -1 ) for SRD, was calculated accordingly: Where md (in mg), is the powder mass loaded into the dustiness system, and   ̅̅̅̅̅ is the average number-based emission rate during the 60 s rotation (s -1 ) determined by Eq.8.
for CD was calculated according to the following equation (EN 17199-3:2019): where  ̅ , is the average number concentration measured by the CPC (in cm -3 ),  ̇ is the volume air flow rate of the CD (53 000 cm 3 min -1 ),   is the whole test duration (9 min) and  0 is the mass fed during the whole test duration (in mg).Table S3.Defined handling energy factors for each experiment by using the data from the SRD and CD dustiness methods.The handling energy factors marked grey with the symbol asterisk (*) resulted from the gravimetrical analysis of the filters collected during the drop tests which might have higher uncertainties (below detection limit or mass that was probably lost during filter handling).N/A: Not available data.G: Grubbs' test statistic is the difference between the sample mean and either the smallest or largest data value, divided by the standard deviation.P: The p-value is a probability that measures the evidence against the null hypothesis.A smaller p-value provides stronger evidence against the null hypothesis.

Figure S1 .
Figure S1.Pictures of the test chamber and sampling positions.

Figure S2 .
Figure S2.Number-based average emission rates based on CPC data obtained by a) the SRD dustiness method, and b) the CD dustiness method.

Figure S3 .
Figure S3.Mean particle number size distributions in a) the SRD dustiness method by ELPI, and b) the CD method by SMPS and APS, TSI.Error bars show the standard deviation.

Figure S4 .
Figure S4.Averages of particle concentrations measured during the drop tests as a function of drop height: a) maximum of particle number concentration; b) mean respirable particle mass concentration; c) mean inhalable particle mass concentration.

Figure S5 .
Figure S5.Characterization of particles decay parameter (γ in h -1 ) for clay PoleStar material.Figure a) shows the exponential decay function fitted to the particle number concentrations measured by the NSOPS and CPC in position 1 and b) shows particle size distributions measured by the NSOPS (position 1).Solid and dashed vertical black lines show the start and end time used to derive the decay rates.

Figure S6 .
Figure S6.Characterization of particles decay parameter (γ in h -1 ) for talc material.Figure a) shows the exponential decay function fitted to the particle number concentrations measured by the NSOPS and OPS in position 1 and b) shows particle size distributions measured by the NSOPS (position 1).Solid and dashed vertical black lines show the start and end time used to derive the decay rates.
Figure S6.Characterization of particles decay parameter (γ in h -1 ) for talc material.Figure a) shows the exponential decay function fitted to the particle number concentrations measured by the NSOPS and OPS in position 1 and b) shows particle size distributions measured by the NSOPS (position 1).Solid and dashed vertical black lines show the start and end time used to derive the decay rates.

Figure S7 .
Figure S7.Characterization of particles decay parameter (γ in h -1 ) for clay OpTiMat material.Figure a) shows the exponential decay function fitted to the particle number concentrations measured by the NSOPS and CPC in position 1 and b) shows particle size distributions measured by the NSOPS (position 1).Solid and dashed vertical black lines show the start and end time used to derive the decay rates.

Figure S8 .
Figure S8.First quartile (Q1), median, and third quartile (Q3) box plots of Hi values calculated for respirable and inhalable particle mass and number concentrations for both SRD and CD methods for each of the pouring heights.Bars show the complete data range for each pouring height and symbols * show the outliers.

Figure S9 .
Figure S9.Loading plot for principal component analysis of parameters potentially correlating with Hi calculated for particle mass and number concentrations for both SRD and CD methods.

Figure S10 .
Figure S10.Residual plots for prediction of all Hi values (determined by respirable dustiness mass fraction) for the SRD dustiness method based on the drop height, respirable dustiness mass fractions, VSSA, and amount of powder poured.

Figure S11 .
Figure S11.Residual plots for prediction of all Hi values (determined by respirable dustiness mass fraction) for the CD dustiness method based on the drop height, respirable dustiness mass fractions, VSSA, and amount of powder poured.

Figure S12 .
Figure S12.Residual plots for prediction of all Hi values (determined by number based dustiness index) for the SRD dustiness method based on the drop height, number based dustiness index, VSSA, and amount of powder poured.

Figure S13 .
Figure S13.Residual plots for prediction of all Hi values (determined by number based dustiness index) for the CD dustiness method based on the drop height, number based dustiness index, VSSA, and amount of powder poured.

Figure S14 .
Figure S14.Residual plots for prediction of all Hi values (determined by inhalable dustiness mass fraction) for the CD dustiness method based on the drop height, inhalable dustiness mass fractions, VSSA, and amount of powder poured.

Figure S15 .
Figure S15.Individual calculated Hi values (determined by number based dustiness index), regression curves and functions for the mean, median, and upper 3 rd quartile (Q3) values for SRD (a) and CD dustiness method (b).

Figure S16 .
Figure S16.Individual calculated Hi values (determined by inhalable dustiness mass fraction), regression curves and functions for the mean, median, and upper 3 rd quartile (Q3) values for CD dustiness method.

Table S1 .
Particle concentrations obtained during drop tests.BG: background (5 min before the drop tests); N: particle number concentration; PM4: respirable mass concentration obtained by cumulative gravimetric sampling; GM: geometric mean; GSD: geometric standard deviation; GMD: geometric mean diameter measured by NSOPS; N/A: Not available data.The handling energy factors marked grey resulted from the gravimetrical analysis of the filters collected during the drop tests which might have higher uncertainties.

Table S2 .
Particle number emission rates (S) obtained during drop tests.GM: geometric mean; GSD: geometric standard deviation; N/A: Not available data.

Table S4 .
Outlier test of Hi determined for particle mass and number concentrations for SRD and CD methods considering a normal distribution.Null hypothesis: All data values come from the same normal population Alternative hypothesis: Smallest or largest data value is an outlier Significance level: α = 0.05