Document 4QK6e1jvkrV92qdEdJO5D8rQ1

MDHS Methods for the Determination of Hazardous Substances Health and Safety Laboratory HSE Health & Safety Executive 14/3 General methods for sampling and gravimetric analysis of respirable and inhalable dust February 2000 INTRODUCTION Occurrence, properties and uses 1 This MDHS aims to guide those who wish to measure the concentrations of respirable and/or inhalable dust in air, for the purpose of monitoring workplace exposure. It updates and replaces MDHS 14/2.1 The principal change is that the recommended sampling procedures for inhalable dust have been revised to take account of new data comparing results obtained using different sampling methods for inhalable dust in a range of workplaces.2 This revised guidance seeks to ensure the best possible method performance under real workplace conditions, and to ensure consistency with the requirements of European3 and international4 standards for workplace dust measurement. Requirements of the Control of Substances Hazardous to Health (COSHH) Regulations 1999 2 Those who carry out and supervise the procedures described in this MDHS could be exposed to various hazardous substances, and therefore should be aware of the requirements of the COSHH Regulations.5 These are designed to ensure that the exposure of people at work to substances that could cause health damage is either prevented, or where that is not reasonably practicable, adequately controlled. Employers are required to make an assessment of the health risk created by such work, and to prevent or control exposure to the substances involved. The COSHH Regulations also require that persons who could be exposed to substances hazardous to health receive suitable and sufficient information, instruction and training. Employers must ensure that their responsibilities under the COSHH Regulations are fulfilled before allowing employees to undertake any procedure described in this MDHS. 4 A number of materials hazardous to health occur in the workplace in the form of aerosols, ie suspensions of solid or liquid particles in air. Dust is generally understood to be an aerosol of solid particles, mechanically produced, with individual particle diameters of 0.1 pm upwards. Fume is an aerosol of solid particles generated by condensation from the vapour state usually following the volatilisation of molten metals. The individual particle diameters are typically less than 1 pm, though the existence of multi-particle aggregates is common. Exposure limits have been defined for many individual dusts and fumes.7 In order to demonstrate that personal exposure is adequately controlled, it is usually necessary to determine the concentration of dust present by means of personal sampling. In some cases a direct determination of the dust concentration is all that is needed. In other cases a subsequent analytical technique is applied for the determination of a particular element or compound present in the dust. 5 This publication describes the general methods recommended for the sampling and gravimetric determination of dust concentrations; for some applications (listed in Appendix 1) modified techniques are required and the relevant guidance should be consulted. Where further analysis for specific constituents of the collected sample is required, reference should be made to the appropriate MDHS8 method sheet. HSE Guidance Note HSG1739 gives general guidance on workplace monitoring. Health effects 3 Guidance is given in the Approved Codes of Practices for the Control of Substances Hazardous to Health Regulations (the General COSHH ACOP), the Control of Carcinogenic Substances Regulations (the Carcinogens ACOP) and the Control of Biological Agents Regulations (the Biological Agents ACOP), which are included in a single publication with the COSHH Regulations.6 6 Most industrial dusts contain particles of a wide range of sizes. The behaviour, deposition and fate of any particle after entry into the human respiratory system, and the response that it elicits, depends on the nature and size of the particle.3 For the purposes of occupational hygiene, it is important to consider the concentrations of dust present in different size fractions. 1 Inhalable dust (also termed 'total inhalable dust') 7 Inhalable dust approximates to the fraction of airborne material that enters the nose and mouth during breathing, and is therefore available for deposition in the respiratory tract. This definition of inhalable dust appears in Regulation 2(1) of COSHH. The inhalable fraction depends on the prevailing air movement around the exposed person (wind speed and direction), and on whether breathing is by nose or mouth. It is, however, possible to define a target specification for sampling instruments that approximates to the inhalable fraction, for representative values of breathing rate, and for a person exposed equally to all wind directions. The target specification given by the European Standards Organisation (CEN)3 and the International Standards Organisation (ISO),4 published in the UK as part of BS EN 481:1993, has been adopted in the UK. 8 In previous revisions of this MDHS,1 and in other key HSE publications,7 inhalable dust has been referred to as 'total inhalable' dust, although the two terms are clearly intended to have the same meaning. It has now been established that the sampling methods previously adopted for 'total inhalable' dust, when used as recommended in this updated MDHS, have characteristics that approximate to the BS EN481 target specification (see paragraph 17). Hence, the terms 'total inhalable' and 'inhalable' may be regarded as interchangeable. Respirable dust 9 Respirable dust approximates to the fraction of airborne material that penetrates to the gas exchange region of the lung. The respirable fraction varies for different individuals; however, it is possible to define a target specification for sampling instruments that approximates to the respirable fraction for the average person. The target specification given by ISO and CEN and published in the UK as part of BS EN 481:1993 has been adopted in the UK. Health and safety precautions 10 Information leaflets in HSE's MS(A) series10 are available for several dusty compounds and processes. These summarise the risks involved in working with dusty compounds and what can be done to control them. 11 Guidance Notes in HSE's Environmental Hygiene series11 1a2re* also available for several dusty compounds and processes. These describe measures to prevent and control exposure, emergency procedures and health surveillance. Exposure limits 12 Regulation 7 of the Control of Substances Hazardous to Health Regulations (COSHH) 19995 lays down the requirements for the use of maximum exposure limits (MELs) and occupational exposure standards (OESs) for the purpose of achieving adequate control of worker exposure. 13 The Health and Safety Commission has approved OESs and MELs for a number of dusts and fumes in air. These include long-term (8-hour time-weighted average) and, in some cases, short-term (usually 15 minutes) exposure limits. UK limit values are expressed in terms of either 'total inhalable' dust or respirable dust. Unless otherwise specified (Appendix 1), the sampling methods recommended in this MDHS may be used to compare workplace dust concentrations with these limit values. 14 Maximum exposure limits and occupational exposure standards are published in Tables 1 and 2 of HSE Guidance Note EH 40.7 That publication sets out the indicative criteria used by WATCH and ACTS in making recommendations for limits. The criteria on which some individual limits are based are documented in HSE Guidance Notes EH 6412,13 and EH 65.14 15 The absence of a specific limit in HSE Guidance Note EH 407 *does not mean that a dust or fume is not harmful. Information on the likely hazard to health of such substances can be found in a number of reference works.15,16 Dusty compounds for which no exposure limits are specified are currently subject to the requirements of the COSHH Regulations. These state that a 'dust of any kind' is regarded as hazardous to health when present at a substantial concentration in air. A 'substantial' concentration of dust should be taken as a concentration of 10 mg m-3 (8-hour time-weighted average) of total inhalable dust or 4 mg m-3 (8-hour time-weighted average) of respirable dust, where there is no indication of the need for a lower value. SCOPE Applicability 16 The methods described in this MDHS are suitable for the determination of the concentrations of most dusts and fumes in the workplace. For a few materials special methods exist (see Appendix 1), and reference should be made to the specific method document. Interpretation of results is discussed in HSE Guidance Notes EH407 and HSG173.9 METHOD PERFORMANCE 17 The sampling methods for inhalable and respirable dust described in this MDHS have been evaluated in both laboratory and field-based tests to determine their performance with respect to the BS EN481 target specifications. A pan-European study of inhalable dust sampling methods was carried out to evaluate instrument performance under controlled laboratory conditions, at wind speeds ranging from 0.5 to 4 m/sec.17 A subsequent laboratory-based study extended the performance evaluation to situations with very low external winds.18 Finally, results obtained using different inhalable dust sampling methods have been compared in a range of workplaces.2,19 The results from this body of research have been used to select those methods for which the bias and precision are within acceptable limits20 (see paragraphs 20, 22 and 24). 2 18 The performance of the various respirable dust sampling methods recommended in this MDHS has been evaluated fully and the results published in a number of papers.21,22,23,24,25 This body of research has enabled the sampling methods to be optimised with respect to the BS EN481 target specification for respirable dust sampling. Detection limits 19 The lower limit of detection of gravimetric analysis is determined primarily by the length of the sampling period, the sensitivity of the balance, and the weight stability of the substrate (eg filter) used to collect and weigh the sample. These factors should be chosen to ensure whenever possible that the lower limit of detection is an order of magnitude lower than the appropriate exposure limit. Useful information on how to determine and reduce gravimetric detection limits can be found in an International Standard on gravimetric analysis, currently under preparation.26 Bias Sampler bias 20 The three inhalable dust sampler types recommended in this MDHS are the Institute of Occupational Medicine (IOM) sampler, the conical inhalable sampler (CIS) and the multi-orifice (or sevenhole) sampler. See paragraph 28 for a full description with illustrations. A sampling bias of less than 5% is typical for the IOM inhalable dust sampler, but the conical inhalable and multi-orifice samplers may exhibit larger biases (either positive or negative) under some workplace conditions.17,18 Problematic situations often leading to negative bias are those where there are high winds, for example outdoors, and where large particles are generated by the work process. Positive bias can result from incorrect handling of the CIS and multi-orifice samplers after use, as the sampler design can allow unintended contamination of the filter. Transport procedures that minimise the potential for such contamination are recommended in paragraph 48. 21 Where workers are very close to dust sources, samplers positioned on the upper chest may in some instances be subjected to a localised high dust concentration that does not represent the air breathed by the worker. The presence of this problem can often be detected by the use of additional unpumped personal samplers as described in paragraph 42.22 23 24 22 For respirable dust samplers, bias generally depends strongly on particle size, but should in most circumstances be within 10%.21, 22 Analytical bias 23 Gravimetric analysis should be unbiased provided that the procedures described in paragraph 55 to correct for blank weight changes are followed. Precision 24 The main source of imprecision in the measurement of workplace dust concentrations is the non uniformity of the dust cloud surrounding the worker. Analytical and sampling imprecision is generally very small in comparison. Workplace-based studies using pairs of samplers on each worker have been used to determine the real imprecision in dust sampling results. For inhalable sampling, for example, a second contemporaneous sample on a worker was found to lie within a factor of two of the first sample, on 95% of occasions.19 A similar study with pairs of respirable dust samplers is currently under way. PRINCIPLE 25 A measured volume of air is drawn through a collection substrate such as a filter mounted in a sampler, and the mass of dust collected is determined by weighing the substrate before and after sampling. DUST SAMPLING EQUIPMENT 26 Different instruments are needed according to whether respirable or inhalable dust is to be collected; paragraphs 28 to 30 give specific guidance. The essential features of all systems are a collection substrate such as a filter and a pump for pulling the air through it; the collection substrate may be held within a cassette system placed within the respirable or inhalable sampler. The pump unit must be capable of maintaining smooth flow at the specified rate throughout the sampling period. 27 In personal sampling, the sampler is attached to the wearer within his or her breathing zone, and the pump (if external to the sampler) is connected to it by a length of flexible tubing and worn on a belt, harness, or in a pocket. The breathing zone is the space around the worker's face from where the breath is taken, and is generally accepted to extend no more than 30 cm from the mouth. Personal sampling instruments are normally mounted therefore on the upper chest, close to the collar-bone. Personal sampling for inhalable dust 28 Three examples of personal sampler for inhalable dust are the multi-orifice sampler (Figure 1), the Institute of Occupational Medicine (IOM) sampler (Figure 2) and the conical inhalable sampler (CIS, Figure 3). The multi-orifice and IOM samplers require a pump unit capable of maintaining a smooth flowrate of 2.0 0.1 litre/min throughout the sampling period. The CIS operates at a higher flow rate, and requires a pump unit capable of maintaining a smooth flowrate of 3.5 0.1 litre/min throughout the sampling period. For details of suppliers see Appendix 2. Other types of sampling instrument may also give satisfactory performance, although the equivalence of results for the substances of interest should be established.26 Of the three sampler types depicted, the IOM sampler has been shown to give the best agreement with the BS EN481 target specification for the inhalable fraction, under the widest range of workplace conditions, and is therefore usually the preferred method of sampling (see paragraphs 17 to 24). Special precautions are 3 to pump Figure 1 Multi-orifice total inhalable sampler End cap with seven equispaced inlet holes 4mm dia. Figure 2 IOM inhalable sampler IWYVCI UdU Fi ter support 37mm filter Cassette upper part Conical inlet Figure 3 Conical inhalable sampler Retaining rng Figure 4 Cyclone respirable sampler 5 48 Transport the samples to the laboratory in a container designed to prevent damage in transit, and labelled to ensure proper handling. Carefully inspect the transport containers, clips etc for signs of loose material lost from the filters. In cases where losses are suspected, it may be necessary to develop and document special transport procedures for the used samplers. Special precautions to recover lost material, for example the use of weighable cassette covers and filter containers, are likely to be needed where samples are sent by post. GRAVIMETRIC ANALYSIS EQUIPMENT Filters 49 If sampling is carried out solely for the measurement of the gravimetric concentration, without analysis, glass fibre filters may be used. Fibre loss from such filters may occur during handling and may be significant if less than 1 mg of dust is collected. At such concentrations, silver, teflon or membrane filters should be used. Some types of filter (eg cellulose nitrate) can show excessive weight change due to moisture absorption, and other types (eg PVC, teflon) can show excessive static build-up. Filters made of mixed esters of cellulose do not have these drawbacks to the same degree. If analysis of the collected material is required, this is likely to determine the choice of filter, and the appropriate MDHS or other method sheet should be consulted. 50 The diameter of the filter needed will, in general, be dictated by the sampling apparatus used. For the instruments described in this MDHS, filter sizes of either 25 mm or 37 mm are required. Smaller filters have lower tare weights, but larger filters have lower resistance, and this may assist in maintenance of the correct flowrate. Other substrate and cassette materials 51 The CIP10 sampler utilises a porous polyurethane foam substrate to collect particles, held in a small plastic cup that is weighed together with the foam. The IOM sampler utilises an internal cassette made of either plastic or metal that is weighed together with the filter it contains, as dust is collected on the inner walls of the cassette as well as on the filter. The IOM dual-fraction respirable sampler collects inhalable dust in the whole cassette, and respirable dust on the filter only. Consult the manufacturer's instructions when weighing samples taken with these instruments. Foams and plastic materials used for filter holders and cassettes may show large weight variations due to moisture absorption, unless the temperature and humidity of the conditioning and weighing environment is carefully controlled (or naturally stable). Balance 52 The balance should have a range that easily accommodates the tare weights of the substrates, cassettes etc, and has readability (ie the finest division on the scale) of 0.01 mg or better. The pan should be large enough to accommodate the substrates used. 53 It should be noted that the reproducibility of weighing on a balance is usually substantially worse than might be expected from the finest division of the scale. Repeat weighing of unexposed substrates over several days is a better guide to true performance. The detection limit of the gravimetric analysis for a particular application can be estimated as approximately three times the standard deviation of weight changes of the group of three blank substrates included in each batch of samples, weighed before and after sampling.29 The magnitude of the blank weight changes can be minimised by choosing less moisture-retentive substrate materials, or by better control of the temperature and humidity of the weighing environment. WEIGHING PROCEDURE Weighing the samples 54 The weight of dust collected is determined by weighing the substrates (in cassettes, where used) both before and after sampling. As a minimum, the accuracy of the balance should be checked with a calibrated standard weight at the intervals recommended by the balance manufacturer. For accurate determination of sample weights, the substrates should be conditioned by being placed in individual, labelled, clean tins (or other suitable containers), and left with the lids slightly ajar in the weighing environment overnight before each weighing. This time period is usually sufficient to allow moisture in the substrates to come into equilibrium with the weighing room atmosphere, although it should be noted that some types of substrate or cassettes may take longer to equilibrate.26 In such cases the use of blanks to correct for weight changes due to moisture absorption is particularly important. The substrates should also be passed over the static eliminator before weighing to dissipate any electrostatic charge. After sampling, the conditioning procedure should be repeated before re-weighing. 55 Weight changes in the used sample substrates caused by variations in atmospheric conditions are corrected by weighing the blank substrates at the same time as the sample substrates, both before and after sampling. The average weight change of the blank substrates is subtracted from the weight change of each sample substrate, in order to calculate the net weight gain. Calculation of dust concentration 56 The volume of air passing through the sampler is calculated by multiplying the mean volumetric flow rate in cubic metres per minute by the sampling time in minutes. (Note: flowrate in litre/min = 1000 x flowrate in m3/min.) The net weight gain (mg) of the sample substrate is divided by the volume of air sampled (m3) to give the average dust concentration in milligrams per cubic metre of air (mg/m3). 57 Where an unpumped sampler has been used alongside a pumped sampler on the same worker, the mass of material collected on the unpumped sampler would normally be expected to be between 5 and 20% of the mass collected on the pumped sampler over the same 8 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 6/3 Lead atomic absorption (AA) 10/2 Cadmium AA 12/2 Chromium AA 14/3 Respirable and inhalable 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 35/2 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 KBr disc 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 46/2 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) 52/3 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 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 moblle phase ion chromatography 80 Volatile organic compounds diffusive/thermal desorption/GC 81 Dustiness of powders and materials 82 The dust lamp 83 Resin acids GC 84 Oil mist from mineral oil-based metalworking fluids 85 Triglycidyl isocyanurate in air pumped filter/ desorption/liquid chromatography 86 Hydrazine in air 87 Fibres in air 88 Volatile organic compounds in air diffusive/solvent desorption/GC 89 Dimethyl sulphate and diethyl sulphate thermal desorption/GC-mass spectrometry 90 Alkyl 2-cyanoacrylates liquid chromatography 91 Metals and metalloids XRF 92 Azodicarbonamide high performance liquid chromatography 93 Glutaraldehyde HPLC 94 Pesticides pumped filters/sorbent tubes/GC Crown copyright 2000 Applications for reproduction should be made in writing to: Copyright Unit, Her Majesty's Stationery Office, St Clements House, 2-16 Colegate, Norwich NR3 1BQ All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. HSE BOOKS MAIL ORDER HSE priced and free publications are available from: HSE Books, PO Box 1999, Sudbury, Suffolk CO10 2WA Tel: 01787 881165 Fax: 01787 313995 RETAIL HSE priced publications are available from good booksellers HEALTH AND SAFETY ENQUIRIES HSE InfoLine Tel: 08701 545500 or write to: HSE Information Centre, Broad Lane, Sheffield S3 7HQ HSE home page on the World Wide Web: http://www.hse.gov.uk First published 1986 Second impression 1997 12.00 net ISBN 0-7176-1749-1 9 7807 7 617494 12 Printed and published by the Health and Safety Executive C10 02/00