Evaluation of the penetration characteristics of a high flow rate personal cyclone sampler for NIOSH ECM/2011/03. Project Leader: Andrew Thorpe

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1 Harpur Hill, Buxton Derbyshire, SK17 9JN T: +44 (0) F: +44 (0) W: Evaluation of the penetration characteristics of a high flow rate personal cyclone sampler for NIOSH ECM/2011/03 Project Leader: Andrew Thorpe Author(s): Andrew Thorpe Unit: Occupational Hygiene Unit

2 DISTRIBUTION Mr Alan Echt Dr Andrew Curran Mr Tim Roff Industrial Hygienist, NIOSH HSL Director of Science and Resources HSL Occupational Hygiene Unit Head PRIVACY MARKING: RESTRICTED: COMMERCIAL This report and the work it describes, were undertaken by the Health and Safety Laboratory under contract to NIOSH. Its contents, including any opinions and/or conclusions expressed or recommendations made, do not necessarily reflect policy or views of the Health and Safety Executive. HSL report approval: Mr T Roff Date of issue: 19 th December 2011 Job number: PE01355 Registry file: Electronic file name: HSL Report

3 CONTENTS 1 INTRODUCTION METHOD ANALYSIS RESULTS Variation in D 50 value as a function of cyclone flow rate Calculation of sampler bias DISCUSSION AND CONCLUSIONS REFERENCES iii

4 EXECUTIVE SUMMARY Objectives To determine the penetration characteristics of a high flow rate personal respirable cyclone sampler, designed and manufactured for the National Institute for Occupational Safety and Health (NIOSH) by BGI Inc. Main Findings The GK4.162 cyclone sampler was found to conform to the respirable sampling convention defined in EN481 (1993) at flow rates between 8.5 & 9.5 l min -1. Between these flow rates, the measured D 50 was between 2-8% of the target value of 4 µm and the sampler met the bias performance criteria (BPC) which states that 85% of all the calculated sampler biases should be within +/- 10% for size distributions with mass median aerodynamic diameters (MMAD) between 1 & 30 and geometric standard deviations (GSD) between 1.75 & 4. iv

5 1 INTRODUCTION The National Institute for Occupational Safety and Health (NIOSH) requested that HSL carry out a determination of the penetration characteristics of a high flow rate personal respirable cyclone sampler manufactured by BGI Inc. The cyclone sampler, identified as GK4.162, was supplied together with a filter cassette. 1

6 2 METHOD The evaluation method was consistent with that described in BS EN 13205, Workplace atmospheres Assessment of performance of instruments for measurement of airborne particle concentrations (CEN, 2002). The design of the test system was based on that described by Kenny and Liden (1991) used for the measurement of aerosol penetration through cyclone samplers. The approach requires measurements of the aerodynamic size distribution of an aerosol penetrating through a selection stage under test and that of the aerosol challenging it. The two size distributions are compared to obtain the penetration characteristics of the selection stage. A polydisperse aerosol of glass ballotini (Spheriglass 5000 CP00) was generated in a calm air chamber using a Palas rotating brush generator (RBG). The charge level on the aerosol was reduced using an ionising air blower. This helped to produce an aerosol that was both stable with time and position within the chamber. The cyclone sampler was attached to the sampling tube in such a way as to allow the inlet to be as close to the vortex finder as possible. The method of attachment is shown in Fig 1. Fig 1. Photograph of the coupling between the APS inlet tube and the GK4.162 cyclone The particle size distribution of aerosol drawn through the cyclone was analysed using a TSI aerosol particle sizer (APS 3321, TSI Inc) and compared with aerosol drawn through an identical set of tubing, but with no cyclone attached. The latter was measured as the challenge aerosol (reference). The dust generator was adjusted to give a concentration of particles that resulted in good penetration results, but which was not so high as to create particle coincidence errors within the APS instrument. The experimental set up is shown in Fig 2. 2

7 Fig 2. Experimental test chamber set up The cyclone was characterised over a range of flow rates from 7-10 l min -1 using the following method. Samples of one-minute duration were drawn through each system in turn, allowing a 1-minute gap between samples to ensure complete replacement of aerosol in the tubing. In each case 3 reference and 2 cyclone penetration samples were taken. Three repeat measurements were made at each flow rate. 3

8 3 ANALYSIS Using an Excel spreadsheet, reference and cyclone sampler particle concentrations were averaged at each particle size, and cyclone penetration measured as a fraction of the reference aerosol. This data was transferred to TableCurve curve-fitting computer program, where the calculated fractional penetration was normalised to 1 at 1 µm to eliminate effects caused by non-linearity of the APS inlet below this size. The D 50 was then determined from the fitted curves. The measured performance data for the cyclone at each flow rate was assessed against the respirable target convention defined in EN 481(1993), using the bias map approach described in BS EN (CEN, 2001). The bias between the fitted performance curve and the target convention for an array of challenge size distributions, specified in the BS EN was calculated. The standard states that a sampler (in this case, cyclone) is in conformance, if 85% of the results lie within the agreed boundary, in this case a bias of ± 10%. 4

9 4 RESULTS Throughout the tests, the aerosol inside the test chamber was found to be extremely stable with very little temporal fluctuation in concentration. The cyclone flow rate was checked before and after each test and was found to be within 1% of the target value. All of these factors contributed to produce measurements that were extremely repeatable, confirmed by the excellent fit to the data shown in Fig VARIATION IN D 50 VALUE AS A FUNCTION OF CYCLONE FLOW RATE Table 1 and Fig 3 shows how the D 50 value (the aerodynamic size at which 50% of the particles penetrate the cyclone) varies as a function of sampler flow rate. The D 50 value was determined using Tablecurve curve fitting software, by carrying out multiple curve fitting algorithms to the data. Table 1. Measured D 50 values for a range of cyclone flow rates Flow rate (l min -1 ) Test 1 Test 2 Test 3 Average Standard COV (%) Deviation D y = e x R 2 = D Flow rate (l min -1 ) Fig 3. Measured D 50 value as a function of cyclone flow rate 5

10 4.2 CALCULATION OF SAMPLER BIAS The following results show the penetration curves, D 50 values and the sampler bias at the various flow rates tested. The respirable convention, defined in EN 481 (1993), is also shown in the figures for comparison Sampler flow rate - 7 l min -1 The measured D 50 at this flow rate is within 22% of the target D 50 of 4 µm The bias map in Figure 4 shows that for many size distributions, the bias does not lie within +/- 10%. Therefore, the sampler does not conform to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10% I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 7 7a 7b Mean SD Target Fractional penetration Aerodynamic diameter (µm) 4 # # # # # 16 # # # # # # # # # # # # # # # # # # # # # # # # 0 to 10 % 3.75 # # # # # 16 # # # # # # # # # # # # # # # # # # # # # # # # 10 to 20 % 3.5 # # # # # 16 # # # # # # # # # # # # # # # # # # # # # # # # 20 to 30 % 3.25 # # # # # 17 # # # # # # # # # # # # # # # # # # # # # # # # > 30% GSD 3 # # # # # 18 # # # # # # # # # # # # # # # # # # # # # # # # 0 to -10% # # # # 19 # # # # # # # # # # # # # # # # # # # # # # # # -10 to -20 % # # # # 20 # # # # # # # # # # # # # # # # # # # # # # # # -20 to -30 % # # # # 22 # # # # # # # # # # # < -30 % 2 7 # # # # 26 # # # # # # # # # Excl dist # # # # 32 # # # # # # MMAD (µm) Fig 4. Performance of the GK4.162 personal cyclone sampler at 7 l min -1 6

11 4.2.2 Sampler flow rate - 8 l min -1 The measured D 50 at this flow rate is within 8% of the target D 50 of 4µm The bias map in Figure 5 shows that for many size distributions, the bias does not lie within +/- 10%. Therefore, the sampler does not conform to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10% I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 8c 8d 8e Mean SD Target Fractional penetration Aerodynamic diameter (µm) # 10 # # # # # # # # # # # # # # # # # # # # # # # # 0 to 10 % # # 10 # # # # # # # # # # # # # # # # # # # # # # # # 10 to 20 % # # 10 # # # # # # # # # # # # # # # # # # # # # # # # 20 to 30 % # # 10 # # # # # # # # # # # # # # # # # # # # # # # # > 30% GSD # # 11 # # # # # # # # # # # # # # # # # # # # # # # # 0 to -10% # # # 11 # # # # # # # # # # # # # # # # # # # # # # # # -10 to -20 % # # # 11 # # # # # # # # # # # # # # # # # # # # # # # # -20 to -30 % # # # 12 # # # # # # # # # # # < -30 % # # # 13 # # # # # # # # # Excl dist # # # 14 # # # # MMAD (µm) Fig 5. Performance of the GK4.162 personal cyclone sampler at 8 l min -1 7

12 4.2.3 Sampler flow rate l min -1 The measured D 50 at this flow rate is within 2% of the target D 50 of 4µm The bias map in Figure 6 shows that for all size distributions, the bias lies within +/-10%. Therefore, the sampler conforms to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10%. I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 8.5c 8.5d 8.5e Mean SD Target Fractional penetration Aerodynamic diameter (µm) to 10 % to 20 % to 30 % > 30% GSD to -10% to -20 % # -20 to -30 % < -30 % # # # Excl dist # # # # MMAD (µm) Fig 6. Performance of the GK4.162 personal cyclone sampler at 8.5 l min -1 8

13 4.2.4 Sampler flow rate - 9 l min -1 The measured D 50 at this flow rate is within 2% of the target D 50 of 4µm The bias map in Figure 7 shows that for many size distributions, the bias lies within +/-10%. Therefore, the sampler conforms to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10%. I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 9c 9d 9e Mean SD Target Fractional penetration Aerodynamic diameter (µm) to 10 % to 20 % to 30 % # > 30% GSD # # # # # # # # 0 to -10% # # # # # # # # # # # # # # -10 to -20 % # # # # # # # # # # # # # # # # # # -20 to -30 % # # # # # # # # < -30 % # # # # # # # # Excl dist # # # # # # MMAD (µm) Fig 7. Performance of the GK4.162 personal cyclone sampler at 9 l min -1 9

14 4.2.5 Sampler flow rate l min -1 The measured D 50 at this flow rate is within 8% of the target D 50 of 4µm The bias map in Figure 8 shows that for many size distributions, the bias lies within +/-10%. Therefore, the sampler conforms to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10%. I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 9.5c 9.5d 9.5e Mean SD Target Fractional penetration Aerodynamic diameter (µm) # # # # # # # # # # # # # # # # # # # 0 to 10 % # # # # # # # # # # # # # # # # # # # # # 10 to 20 % # # # # # # # # # # # # # # # # # # # # # # 20 to 30 % # # # # # # # # # # # # # # # # # # # # # # # > 30% GSD # # # # # # # # # # # # # # # # # # # # # # # # 0 to -10% # # # # # # # # # # # # # # # # # # # # # # # # -10 to -20 % # # # # # # # # # # # # # # # # # # # # # # # # -20 to -30 % # -3 # # # # # # # # # # # < -30 % # -5 # # # # # # # # # Excl dist # # -11 # # # # # # MMAD (µm) Fig 8. Performance of the GK4.162 personal cyclone sampler at 9.5 l min -1 10

15 4.2.6 Sampler flow rate - 10 l min -1 The measured D 50 at this flow rate is within 13% of the target D 50 of 4µm The bias map in Figure 9 shows that for many size distributions, the bias does not lie within +/-10%. Therefore, the sampler does not conform to the Bias Performance Criteria (BPC) that 85% of all the calculated biases are within +/- 10%. I.D. D50 (µm) Cyclone penetration CEN 481 (respirable) 10c 10d 10e Mean SD Target Fractional penetration Aerodynamic diameter (µm) # # # # # # # # # # # # # # # # # # # # # # # # 0 to 10 % # # # # # # # # # # # # # # # # # # # # # # # # 10 to 20 % # # # # # # # # # # # # # # # # # # # # # # # # 20 to 30 % # # # # # # # # # # # # # # # # # # # # # # # # > 30% GSD # -2 # # # # # # # # # # # # # # # # # # # # # # # # 0 to -10% # -2 # # # # # # # # # # # # # # # # # # # # # # # # -10 to -20 % # -4 # # # # # # # # # # # # # # # # # # # # # # # # -20 to -30 % # # -6 # # # # # # # # # # # < -30 % # # -9 # # # # # # # # # Excl dist # # -16 # # # # # # MMAD (µm) Fig 9. Performance of the GK4.162 personal cyclone sampler at 10 l min -1 11

16 5 DISCUSSION AND CONCLUSIONS The GK4.162 cyclone sampler was found to conform to the respirable sampling convention defined in EN481 (1993) at flow rates between 8.5 & 9.5 l min -1. Between these flow rates, the measured D 50 was between 2-8% of the target value of 4 µm and the sampler met the bias performance criteria (BPC) which states that 85% of all the calculated sampler biases should be within +/- 10% for size distributions with mass median aerodynamic diameters (MMAD) between 1& 30 and geometric standard deviations (GSD) between 1.75 & 4. 12

17 6 REFERENCES European Committee for Standardisation (CEN) (1993). Workplace atmospheres Size fraction definitions for measurement of airborne particles. CEN Standard EN 481, Brussels. CEN (1993). European Committee for Standardisation (CEN) (2002). Workplace atmospheres Assessment of performance of instruments for measurement of airborne particle concentrations. CEN Standard EN 13205, Brussels. CEN (2002). Kenny L C, Liden G. (1991) A technique for assessing size selective dust samplers using the APS and polydisperse test aerosols. Journal of Aerosol Science. 22,