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MDHS Methods for the Determination of Hazardous Substances Health and Safety Laboratory 81 Dustiness of powders and materials HSE Health & Safety Executive September 1996 INTRODUCTION 1 The control of dust emission during the production, handling and transportation of powders and materials is an important consideration in the design and operation of industrial processes. 2 Excessive airborne dust levels in workplaces are undesirable for a number of reasons: a) they can cause adverse health effects; b) their control can involve the use of costly ventilation and filtration systems; c) they can be costly in terms of lost product; d) they can contaminate machinery and products. Factors (a) and (b) mean that knowledge of the propensity of a material to release dust may be required by those responsible under the Control of Substances Hazardous to Health Regulations (COSHH) for assessing the likely health risk from materials or for controlling dust emissions. Although factors (c) and (d) may have no direct bearing on health, their economic impact could be significant. 3 Dusts emitted during the handling of powders and materials contain particles of a wide range of sizes. The likely health risk from inhalation of a specific particle is dependent upon the nature and size of the particle. The International Standards Organisation (ISO) and the Comite Europeen de Normalisation (CEN) have published conventions for health-related sampling.1,2 The three main size fractions are inhalable, thoracic and respirable. This publication describes a method for determining the dustiness of materials, based on these three internationally recognised health-related fractions. Other methods based on different principles are also available and have a range of applications.3 DEFINITIONS 4 The dustiness of a material is defined as the propensity of that material to produce airborne dust when handled.3 5 The inhalable fraction EI is the mass fraction of total airborne particles which is inhaled through the nose and mouth. The ISO and CEN standards specify that samplers for this fraction should have a collection efficiency: E, = 50(1 + exp[-0.06D]) where D is the particle aerodynamic diameter, and E, is expressed as a percentage. 6 The thoracic fraction ET is the mass fraction of inhaled particles penetrating beyond the larynx. The CEN and ISO convention for this fraction declines from 100% at 0 pm with the shape of a cumulative log-normal curve with a median diameter of 11.64 pm and a geometric standard deviation of 1.5. 7 The respirable fraction ER is the mass fraction of inhaled particles which penetrates to the unciliated airways. The CEN and ISO convention for this fraction declines from 100% at 0 pm with the shape of a cumulative log-normal curve with a median diameter of 4.25 pm and a geometric standard deviation of 1.5. SCOPE OF THE METHOD 8 The method described is suitable for the determination of the health-related dustiness of powders and materials in use in industrial processes, including powders, pelletised material and loosely-packed fibrous material. 9 The lower limit of detection for the dustiness value for each health-related fraction is governed by the accuracy of the weighing procedures. If emitted dust levels are too low to allow reliable measurements of the three fractions separately, the particle size-selective stages can be removed and results for one combined fraction - an approximation to the inhalable fraction - can be obtained. 1 PRINCIPLE 10 A measured mass of material is tumbled in a rotating drum, through which air is passed at a known flowrate for a fixed time. The resulting dust cloud is passed through a three-stage dust sampling system, comprising two sizeselective foams and a filter. The masses of dust collected are determined by weighing the foams and filters before and after the measurement run. The total amount of dust collected gives a measure of the dustiness in terms of the inhalable fraction. Values for the dustiness of the material in terms of the thoracic and respirable fractions are also calculated from the amounts passing through the sizeselective foams.4 APPARATUS Dustiness test apparatus 11 The apparatus required to determine the dustiness of materials is shown in Figure 1. Sets of engineering drawings are available from the Health and Safety Laboratory, for a small charge, to enable the apparatus to be constructed. Alternatively the complete test apparatus is available from JS Holdings, Stevenage (see Appendix 2 for addresses). The apparatus comprises a 300 mm diameter drum rotating at 30 rpm, equipped with longitudinal vanes to lift and let fall 200 g of the material under test, and a threestage dust sampling system (the outlet stage) through which the emitted dust cloud is drawn by a vacuum pump at a flowrate of 38 l min-1 for 1 minute. The sampling system comprises two particle sizeselective foams in series followed by a back-up filter. Dust entering the conical passage and into the sampling system gives an estimate of the inhalable fraction. The size selectors, in the form of cylindrical plugs of 30 pores per inch (ppi) and 90 ppi porous polyester foam, are chosen to select the thoracic and the respirable fractions, respectively. The foams and the back-up filter are weighed before and after the test to provide the dustiness estimates of the three size fractions. An identical set of foams and filter is positioned at the inlet to the drum (inlet stage), and serve as controls by taking account of weight changes due to the passage of air through the foams and filter. Extra filters are positioned either side of the inlet stage to prevent dust contamination. The flowrate through the device is monitored using an in line rotameter and the volume of air sampled is measured with a calibrated gasmeter. The operation of the apparatus is automatically controlled by a timing control circuit. Size-selective foams 12 Porous polyester foam size selectors with a reticulated open-cell structure are used to select the thoracic and respirable dust fractions. These are manufactured by Recticel PRB in Belgium, and are available in the UK from Foam Engineers Ltd, High Wycombe (see Appendix 2 for addresses). Both size selectors are 150 mm diameter, 25 mm thick foam plugs, and they are housed in carrier frames to facilitate both handling and weighing. Filters 13 150 mm diameter reinforced glass fibre filters (for example, GF/A filters made by Whatman) are used to collect the fine respirable particles that penetrate the foams. Ancillary equipment 14 The balance room or chamber where weighing is carried out should have temperature and humidity maintained at a stable level. A balance capable of weighing 250 g with a reproducibility of 0.1 g should be available for weighing the samples of test material. A balance capable of weighing 150 g with a reproducibility of 0.1 mg should be used for accurate determination of the foams and filters. The weighing chamber of the balance should be large enough to hold a 150 mm foam carrier without it touching the walls. A weighing frame to position the foams and filters on the balance pan may be used. PROCEDURE 15 Detailed instructions are given in Appendix 1. The following is a summary of key stages. Preparation of test sample 16 A test sample should be prepared from the bulk material using a method which would result in representative sampling. Methods given in BS34065 should be used. Sealable sample bottles should be used to minimise spread of contamination. Each test sample should weigh 200 g + 0.1g. Preparation of apparatus 17 Prior to the tests being carried out, the rotating drum is cleaned thoroughly using a suitable vacuum cleaner and wiped with a damp cloth. For material that sticks to the internal surfaces it may be necessary to wash the surfaces with a solution of a detergent in water followed by thorough washing with water, or to clean with a suitable solvent (for example, propan-2-ol), and allow the apparatus to dry. Assemble the inlet and outlet stages to appropriate ends of the drum. Switch on the pump and set the flowrate to 38 l min-1. Running the test 18 Remove the inlet and outlet stages at both ends of the drum. Replace the inlet stage with a fresh set of foams and filter. Spread the sample evenly along the bottom of the drum. Assemble the outlet stage to the drum. 2 Inlet stage Figure 1 Schematic diagram showing the main features of the test apparatus 3 19 The timing circuit is then switched on and the test programme allowed to proceed. At the end of the test, carefully remove the foams and the filters from either end of the drum and place them in the balance room, taking care not to disturb the collected dust. Weighing the foams and filters DETERMINATION OF THE DUSTINESS VALUES 23 The dustiness values for each fraction are calculated using the equations shown in Figure 2.6 At least three replicate tests should be carried out for each material and the mean values are then calculated for each fraction, together with the standard deviation. 20 The weight of dust collected is determined by weighing the foams and filters before and after the test. They should be weighed in their carriers following a defined sequence. After the test, the foams and filters are reweighed in the same sequence. As the foams are sensitive to moisture and electrostatic conditions in the atmosphere, it is essential that a protocol be followed as to when the weight indicated by the balance should be recorded. It is recommended that the weight be taken 30 seconds after the specimen is placed on the balance pan and the balance door closed. REPORTING OF RESULTS 24 The dustiness of the test material is reported in terms of (DI, Dt, Dr). For example, a dustiness value of (4, 20, 5) means that 4% of the dust tested became airborne and was collected as inhalable dust; that 20% of the inhalable fraction was able to penetrate past the larynx (thoracic); and that 5% of the inhalable fraction was able to penetrate past the unciliated airways (respirable). 21 In order to minimise the risk of contamination it is recommended that handling of the foam carriers should be kept to a minimum. Gloves should be worn or tweezers used to lift or carry the foams and only tweezers used when handling the filters. If the weight of either of the control (30 and 90 ppi) foams changes by more than 20 mg it would indicate contamination or loss of foam material. The measurement should be repeated with a fresh sample. 25 If the masses of dust collected on the foams are too low for meaningful results to be obtained, tests may be carried out in which both foams are omitted and all the dust collected on the filter to give an indication of the inhalable fraction dustiness value only, ie (DI, -, -). HEALTH AND SAFETY 22 The weights of dust captured in the size-selecting stages are calculated in the following equation: Dn = (VTJ - (CFn"CIn) where Dn = Weight of dust captured on the n th stage TFn = Final weight of the n th test stage TIn = Initial weight of the n th test stage CFn = Final weight of the n th control stage CIn = Initial weight of the n th control stage The n th stage corresponds to the 30 ppi foam, the 90 ppi foam or the backing filter in the foam/filter assembly. This process allows for any weight changes in the foams and filters during the test to be corrected. 26 This work may be subject to the Control of Substances Hazardous to Health (COSHH) Regulations 1994 (or to the Control of Lead at Work Regulations 1980 or the Control of Asbestos at Work Regulations 1987, if the materials contain lead or asbestos). HSE guidance on the appropriate regulations should be consulted.7,8,9 In general, it will be necessary to assess the risk to health from exposure to the substances used, to assess the measures necessary to comply with the regulations, and to prevent or adequately control exposure, taking into account applicable occupational exposure limits.10 The assessment should take account not only of the materials tested, but of others used, such as cleaning solvents; and not only of exposure by inhalation, but of other routes such as skin absorption. Figure 2 weight gain on the two test foams + weight gain on the backing filter DI = -------------------------------------------------------------------------------------------- weight of test sample x 100% weight gain on the 90 ppi test foam and backing filter Dt= weight gain on the two test foams + weight gain on the backing filter x 100% weight gain on the backing filter DR = weight gain on the two test foams + weight gain on the backing filter where DI = the dustiness value of the inhalable dust fraction; Dt = the dustiness value of the thoracic fraction; and Dr = the dustiness value of the respirable fraction. x100% 27 Other physical hazards should also be considered. Explosion risks may result from the material becoming airborne; in particular organic dusts can form explosive mixtures with air at concentrations above the lower explosive limit.11,12 Precautions such as earthing the tester to minimise the build-up of static electricity, removal of hot surfaces and flame from the vicinity of the test should be introduced. ADVICE 28 Advice on this method and the equipment used may be obtained from the Aerosols Section, Health and Safety Laboratory, Health and Safety Executive, Broad Lane, Sheffield S3 7HQ (telephone 0114 289 2000, fax 0114 289 2500 or e-mail aerosols@dust.demon.co.uk). The Health and Safety Executive wishes, wherever possible, to improve the methods described in this series. Any comments that might lead to improvements would, therefore, be welcome and should be sent to the above address. REFERENCES 1 International Standards Organisation Air quality particle size fraction definitions for health-related sampling ISO 7708 - 1995 ISO. 2 Comite Europeen de Normalisation Workplace atmospheres - size fraction definitions for the measurement of airborne particles BS EN 481 - 1993 British Standards Institution. 3 British Occupational Hygiene Society Technical Guide No. 4 - Dustiness estimation methods for dry materials Science Reviews Ltd 1985 ISBN 0 905927 71 0. 4 Lyons C P and Mark D Development and testing of a procedure to evaluate the dustiness of powders and dusts in industrial use HSE Contract Research Report No 62/1994 HSE Books 1994 ISBN 0 7176 0727 5. 5 British Standards Institution BS3406: Part 1:1986 Determination of particle size distribution - Part 1: Guide to powder sampling BSI 1986 ISBN 0 580 15305 3. ACKNOWLEDGEMENT 29 Preparation of this document was overseen by Working Group Two of the Committee on Analytical Requirements. At the time of writing, CAR/WG2 consisted of Dr K Chung, Mr A Griffin, Dr H Jackson, Dr T Ogden and Dr N West (all of HSE), together with Mr C Hammonds (Michelin Tyre plc), Mr D Mark (University of Birmingham) and Dr B Wells (formerly Unilever Research Laboratories). 6 Chung K Y K and Burdett G J Dustiness testing and moving towards a biologically relevant dustiness index Ann occup hyg 38 (1994) 945-949. 7 Health and Safety Executive Control of Substances Hazardous to Health Regulations 1994: Approved Codes of Practice L5 HSE Books 1995 ISBN 0 7176 0819 0. 8 Health and Safety Executive Control of Lead at Work Regulations 1980: Approved Codes of Practice HSE Books 1985 (rev) ISBN 0 11 883780 X. 9 Health and Safety Executive The Control of Asbestos at Work: Control of Asbestos at Work Regulations 1987: Approved Codes of Practice L27 (second edition) HSE Books 1993 ISBN 0 11 882037 0. 10 Health and Safety Executive Environmental Hygiene Series Guidance Note. Occupational exposure limits EH40 HSE Books (updated annually). 11 Field P Dust explosions in Vol 4 of Handbook of powder technology Elsevier 1982 ISSN 0167-3785. 12 Eckhoff R K Dust explosions in the process industries Butterworth Heinemann 1991 ISBN 0 7506 1109 X. 5 APPENDIX 1 Operating procedure for the HSE Rotating Drum Dustiness Tester model EDT38L 4.2.1 Insert a filter in the inlet outer case as the outer guard filter. 1 Context and scope 4.2.2 Insert a filter support grid. 1.1 This Appendix describes how to operate the HSE Rotating Drum Dustiness Tester model EDT38L. The tester is suitable for any dry material. 1.2 The work may be subject to the Control of Substances Hazardous to Health (COSHH) Regulations 1994 (or to the Control of Lead at Work Regulations 1980 or the Control of Asbestos at Work Regulations 1987 if the material contains lead or asbestos). HSE guidance on the appropriate regulations should be consulted. 1.3 Other physical hazards, such as explosivity, should be considered and appropriate measures taken. 4.2.3 Insert one of the preweighed filters as the control filter with its filter support grid. 4.2.4 Clip one of the 30 ppi foam carriers and one of the 90 ppi foam carriers together to form the control foam set and insert into the inlet outer case. 4.2.5 Insert the inner guard filter and a filter support grid. 4.2.6 Attach the inlet stage to the drum and secure with the latches. 4.3 Assembly of the outlet stage (see Figure A.2). 2 Description of equipment 2.1 The EDT38L Dustiness Tester consists of a steel drum which rotates on a pair of rollers. Material inside the drum is lifted up by a system of blades and let drop, thus producing a dust cloud. Dust-laden air is drawn through an assembly of size-selecting foams and filter. The propensity of dust release and size distribution of the airborne component of the material are determined by weighing the foams and filters. 2.2 The tester is housed inside a toughened plastic enclosure. A microswitch is incorporated which will turn off power to the equipment when the lid is not properly down. 4.3.1 Insert a filter support grid and the other preweighed filters into the outlet outer case. 4.3.2 Clip the other 30 ppi foam and 90 ppi foam carriers together to form the sampling foam set and insert into the outer case. 4.3.3 Attach the outer case to the exit end of the drum and secure with the latches. 4.3.4 Connect the outlet of the outlet stage to the rotating coupling with the clasp and secure the wing nut. 4.4 Disassembly of the outlet stage. 3 Equipment required 3.1 The EDT38L assembly, foams carriers, filter cassettes, foams, filters and a suitable balance. 3.2 For materials that are considered hazardous to health it may be necessary to use the equipment inside a fume extraction hood. Suitable personal protection equipment, such as gloves, may also be required. 3.3 Vacuum cleaner fitted with HEPA filter and a hose extension. 4 Main operational procedures 4.1 Preparation. 4.1.1 Check the drum is clean and ready for use. 4.1.2 Insert two 30 ppi foams into their carriers and weigh to 0.1 mg. 4.1.3 Insert two 90 ppi foams into their carriers and weigh to 0.1 mg. 4.1.4 Weigh two 150 mm reinforced ream GF/A glass fibre filters to 0.1 mg. 4.4.1 Undo the wing nut to release the rotating coupling to the outlet stage. 4.4.2 Gently turn the drum on the rollers so that the latches are accessible. 4.4.3 Hold the outlet stage in place with one hand while removing the latches. 4.4.4 Gently slide the stage out and down from the drum and carefully place it on the bench. 4.4.5 Lift the foam carriers out of the outer case and turn the top one gently clockwise to undo the bayonet fitting to release the two foam carriers. 4.4.6 Place both foam carriers on a tray. 4.4.7 Release the bayonet fitting on the assembly case and slide the top piece down. 4.4.8 With two pairs of tweezers carefully lift the filter off its support grid. 4.4.9 Place the filter with the foams for re-weighing. 4.5 Disassembly of the inlet stage. 4.2 Assembly of the inlet stage (see Figure A.1). 4.5.1 Rotate the drum so that the latches are accessible. 6 4.5.2 Hold the inlet stage with one hand and undo the latches. 4.5.3 Gently slide the stage out and down from the drum and carefully place it on the bench. 4.5.4 Lift the foam carriers out of the outer case and turn the top one gently clockwise to release the bayonet fitting to release the two foam carriers. 4.5.5 Place both foam carriers on a tray. proforma A1. 4.7.11 Clean the drum either with a vacuum cleaner and a damp cloth or by washing it out with water. If organic solvent is used, care must be taken not to create a flammable or harmful vapour hazard. 5 Calculation of results 5.1 The dustiness values should be calculated as described in paragraph 23. 4.5.6 Carefully push the outer guard filter up the case until the control filter support grid and the filter can be lifted off, remove the control filter and place it with the control foams for re-weighing. APPENDIX 2 Suppliers of equipment Equipment Supplier 4.6 Flowrate check. 4.6.1 Flowrate check should only be necessary once a week for continuous use, or at the beginning of a test if the equipment has not been used for a long period of time. Rotating Drum Dustiness Tester EDT38L JS Holdings Unit 5 Willows Lane Stevenage Herts SG2 8AB Tel: 01438 316994 4.6.2 Assemble the drum as 4.1 - 4.3. 4.6.3 Press the green switch to turn on the pump. 4.6.4 Adjust the rotameter to 38 l/min. After the first cycle take the reading at the gasmeter. Size-selective foams Foam Engineers Ltd Dashwood Avenue High Wycombe Bucks HP12 3EA Tel: 01494 459537 4.6.5 Press the green button again and read the gasmeter when the pump stops. 4.6.6 Compute the difference between the first gasmeter reading and the second, and if the difference is not within 38 1 l/min adjust the valve at the pump. Reinforced glass fibre filters Whatman International Ltd St Leonard's Road 20/20 Maidstone Kent ME16 0LS Tel: 01662 674821 4.6.7 Repeat 4.6.3 to 4.6.6 until 38 1 I/min is achieved. 4.7 Testing a sample. 4.7.1 Prepare the drum, foams and filters as described in 4.1, and enter the values in proforma A1. 4.7.2 Assemble the inlet stage of the tester as described in 4.2. 4.7.3 Weigh out about 200 g of sample to 0.1 g. 4.7.4 Spread the sample evenly along the bottom of the drum. 4.7.5 Assemble the outlet stage of the tester as in 4.3. 4.7.6 Record the gasmeter reading, the temperature and relative humidity in the laboratory in proforma A1. 4.7.7 Close the lid and press the green button to start the rotation and pump. 4.7.8 Take the gasmeter reading when the drum stops rotating and the pump stops. 4.7.9 Disassemble the drum (4.4 and 4.5). 4.7.10 Weigh the foams and filters, and enter the values in 7 fj Figure A.1 The inlet stage of the HSE Rotating Drum Dustiness Tester model EDT38L 8 30 ppi control Figure A.2 The outlet stage of the HSE Rotating Drum Dustiness Tester model EDT38L 9 0) 10 Proforma A1 - Report Test material/sample number Test conditions Gas meter readings (l/m) Reading befo Reading afte Difference Temperature (C) RH(%) Sample mass (g) Mass of sample + bottle Mass of bottle Mass of sample oOO Ll_ Test components 30 ppi foam Weight before Control weights Test weights (mg) (mg) II II II o 90 ppi foam Filter Weight after Difference Weight before Weight after Difference Weight before Weight after Difference o a> o a> Ll_ o Date Dust collected (mg) Ll_ O a> O o oo II II II oo a> Ll_ 11 TITLES IN THE MDHS SERIES 1 Acrylonitrile charcoal tube/gas chromatography (GC) 2 Acrylonitrile pumped thermal desorption/GC 3 Standard atmospheres syringe injection 4 Standard atmospheres permeation tube 5 On-site validation of methods 6/2 Lead atomic absorption (AA) 7 Lead X-ray fluorescence (XRF) 8 Lead colorimetric (dithizone) 9 Tetra alkyl lead personal monitoring 1 0/2 Cadmium AA 11 Cadmium XRF 12/2 Chromium AA 13 Chromium XRF 14 Total inhalable and respirable dust gravimetric 15 Carbon disulphide charcoal tube/GC 16 Mercury adsorbent tube (Hydrar) AA 17 Benzene charcoal tube/GC 18 Tetra alkyl lead continuous monitoring 19 Formaldehyde colorimetric (Chromotropic acid) 20 Styrene pumped charcoal tube/GC 21 Glycol ethers charcoal tube/GC 22 Benzene thermal desorption/GC 23 Glycol ethers thermal desorption/GC 24 Vinyl chloride charcoal tube/GC 25/2 Organic isocyanates reagent bubbler/HPLC 26 Ethylene oxide charcoal tube/GC 27 Diffusive sampler evaluation protocol 28 Chlorinated hydrocarbons charcoal tube/GC 29/2 Beryllium AA 30/2 Cobalt AA 31 Styrene pumped thermal desorption/GC 32 Phthalate esters solvent desorption/GC 33 Adsorbent tube standards 34 Arsine colorimetric (diethyldithiocarbamate) 35 HF and fluorides ion-selective electrode 36 Toluene charcoal tube/GC 37 Quartz in respirable airborne dust direct infra-red 38 Quartz in respirable airborne dust KBrdisc technique 39/4 Asbestos fibres light microscopy (European reference version) 40 Toluene thermal desorption/GC 41/2 Arsenic AA 42/2 Nickel AA 43 Styrene diffusive/thermal desorption/GC 44 Styrene diffusive/solvent desorption/GC 45 Ethylene dibromide solvent desorption/GC 46 Platinum AA 47 Rubber fume in air measured as total particulates and cyclohexane soluble material 48 Newspaper print rooms: measurements of total particulates and cyclohexane soluble material in air 49 Aromatic isocyanates acid hydrolysis/ diazotisation 50 Benzene diffusive/thermal desorption/GC 51/2 Quartz in respirable dusts X-ray diffraction (direct method) 52/2 Hexavalent chromium in chromium plating mists colorimetric (1,5-diphenylcarbazide) 53 1,3 Butadiene thermal desorption/GC 54 Protocol for assessing the performance of a pumped sampler for gases and vapours 55 Acrylonitrile diffusive/thermal desorption/GC 56/2 Hydrogen cyanide ion-selective electrode 57 Acrylamide liquid chromatography 58 Mercury vapour 59 Manmade mineral fibres 60 Mixed hydrocarbons 61 Total hexavalent chromium compounds in air colorimetric 62 Aromatic carboxylic acid anhydrides 63 Butadiene diffusive/thermal desorption/GC 64 Toluene charcoal diffusive/solvent desorption/GC 65 Mine road dust: determination of incombustible matter 66 Mixed hydrocarbons (C5 to C10) in air diffusive/ thermal desorption/GC 67 Total (and speciated) chromium in chromium plating mists colorimetric (1,5-diphenylcarbazide) 68 Coal tar pitch volatiles 69 Toluene diffusive/solvent desorption/GC 70 General methods for sampling airborne gases and vapours 71 Analytical quality in workplace air monitoring 72 Volatile organic compounds in air 73 Measurement of air change in factories and offices 74 n-Hexane in air diffusive/solvent desorption/GC 75 Aromatic amines solid sorbent/thermal desorption/GC 76 Cristobalite in respirable dusts X-ray diffraction (direct method) 77 Asbestos in bulk materials 78 Formaldehyde diffusive/solvent desorption/liquid chromatography 79 Peroxodisulphate salts mobile phase ion chromatography 80 Volatile organic compounds diffusive/thermal desorption/GC Crown copyright 1996 Applications for reproduction should be made to HMSO All rights reserved. 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