Method for the determination of wood dust

Transcription

1 195 Method for the determination of wood dust German Social Accident Insurance Deutsche Gesetzliche Unfallversicherung Analytical Subcommittee of the Chemistry Board of Experts* Carcinogenic substances Order number: BGI Established methods: Issued: January 2009 This method has been tested and recommended by the German Social Accident Insurance for the determination of wood dust in the air at workplaces. Both personal and stationary sampling can be performed for the assessment of workplaces. Sampling is carried out with a pump thereby the dust being collected on a particle filter. Analysis is performed by gravimetry. * Please direct correspondence to Berufsgenossenschaft RCI, Fachbereich Gefahrstoffe und biologische Arbeitsstoffe, P.O. Box , Heidelberg, Germany; analytik@bgrci.de The MAK-Collection Part III: Air Monitoring Methods, Vol. 13 DFG, Deutsche Forschungsgemeinschaft 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA

2 196 Analytical Methods Summary This method can be used to determine the mean concentration of wood dust in the air at workplaces over the sampling time. Sampling can be carried out with personal or stationary sampling systems Principle: A pump draws a defined volume of air through a particle filter. The mass of the deposited dust is determined by weighing the particle filter before and after sampling. In addition, the collected dust can be burned to ashes in order to determine the loss on calcination (optional). Limit of quantification: The absolute limit of quantification is between 0.45 and 4.5 mg for a sampling time of 8 hours, depending on the sampling system. The relative limit of quantification is between 0.02 mg/m 3 and 0.27 mg/m 3 (based on an air sample volume of 32 m 3 or 1.68 m 3 respectively). Selectivity: Not selective. Advantages: Simple procedure requiring minor technical resources. Disadvantages: Distinction between different types of wood dust or other particulate substances is not or only partially (if the loss on calcination is determined) possible. Apparatus: Pump with sampling head and particle filter, balance, hygrometer, thermometer, annealing furnace (if ashing is performed)

3 Wood dust 197 Detailed description of the method Contents 1 Equipment and materials 1.1 For sampling 1.2 For sample preparation and analysis 2 Sampling procedure 3 Analytical determination 3.1 Conditioning the filters in the room 3.2 Weighing 3.3 Determination of the loss on calcination of the collected dust (optional) 4 Evaluation 5 Reliability of the method 5.1 Precision 5.2 Limit of quantification 5.3 Selectivity 1 Equipment and materials 1.1 For sampling Sampling devices suitable for collecting the inhalable dust fraction as stipulated in DIN EN 481 [1] and that fulfil the requirements of DIN EN [2] (e.g. VC 25G, PM 4F, GSP-10, GSP-BIA from GSA Messgerätebau, Neuss-Norf, Germany) see Section 5.2 Table 1). Glass fiber filters or quartz fiber filters are used that permit the passage of at most 0.5% of a nebulized paraffin oil test aerosol [3, 4] (e.g. MN BF glass fiber filter, Macherey-Nagel GmbH & Co KG, Düren, Germany; GF 6, Schleicher & Schuell GmbH, Dassel, Germany; QF 20 quartz fiber filter, Schleicher & Schuell; Ederol T293, Binzer & Munktell, Battenberg, Germany; Munktell MK 360 quartz microfiber filter, Binzer & Munktell).

4 198 Analytical Methods 1.2 For sample preparation and analysis Analytical balance, if possible equipped with an anti-static device, e.g. electronic balance with a large pan to accommodate filters up to 150 mm in diameter. The following readability of the balance for the final weighing of the filters is sufficient, depending on the diameter of the filter: 0.1 mg for filters with a diameter of 150 mm and 0.01 mg for filters with a diameter of 70 mm or 37 mm Two pairs of tweezers with flat, oblate tips Hygrometer Thermometer Annealing furnace and crucible (if ashing is performed) 2 Sampling procedure A pump draws a defined air volume through a glass fiber or quartz fiber filter that is located in the sampling head of a suitable sampling device (see Section 5.2 Table 1). It is important to seal the filters in their filter cassettes, ensuring that they are dust-tight during transport. The material of the cassette should be such that static charge is avoided as far as possible. Specific aspects of sampling dust and possible sources of error are described in [5]. 3 Analytical determination The weighing of filters before they are loaded and after loading must be carried out in a room with largely constant climatic conditions. Direct sunlight must be avoided (e.g. room on the north side of the building). The balance must be mounted vibration-free, and it should be set up as far as possible from windows, doors and radiators. Vibration-free weighing is possible if the balance is standing on a suitable weighing table or a slab made of closed-cell plastic foam (e.g. polyethylene). A stable metallic support must be placed between the balance and the plastic foam slab. The room temperature and relative air humidity must be regularly checked, as the treatment and weighing of the filters should be performed at a relative air humidity ranging from 30 to 60% and at a room temperature between 18 and 25 C.

5 Wood dust 199 Before each filter weighing the filters must be conditioned as described in Section 3.1. In addition to the determination of the total collected dust (Section 3.2), the part of the dust that cannot be burned to ash can be determined by calcination (Section 3.3). This is advisable if, in addition to wood dust, other kinds of dust in significant concentrations occur at the workplace. Detailed information on storage, transport, conditioning and weighing of the filters is given in [5]. It is particularly important to consider the influence of relative humidity during weighing. This can be taken into account in three ways: Presence of blank filters during sampling: calculation of the limit of quantification based on the mean mass difference between the blank weight before and after sampling. Use of laboratory blank filters in the weighing room: consideration of the relative mass change of the blank masses of sample filters by means of parallel weighing of three laboratory blank filters at the time of the weighing of the sample filters before and after sampling. Calibration with climatic data: calculation of the dependence of the filter mass on relative humidity that is determined in a series of experiments. 3.1 Conditioning the filters in the room Before and after the filters have been loaded with dust, they are removed from their packaging or taken out of the sampling head and placed free in the weighing room, but covered from above in such a way that the filters can acclimatize to the weighing room atmosphere. A conditioning period of 2 days is recommended. If laboratory tests are performed, the optimum duration of conditioning can be stipulated individually. 3.2 Weighing After conditioning, tweezers are used to place the individual filters on the weighing pan, and the mass is determined. If the measurement value display shows drift, the value is read off only when the display has stabilized. The climatic conditions, in particular the relative air humidity and the temperature in the weighing room must be taken into account. Please refer to [5] for further information on weighing.

6 200 Analytical Methods 3.3 Determination of the loss on calcination of the collected dust (optional) After determination of the dust mass on the filter, the loaded filter is calcined for at least 2 hours at 550 C. Then the filter with the residue that cannot be burned to ash is weighed again. If the calcination procedure is carried out, the filters to be used for sampling must also be calcined for at least 2 hours at 550 C before the blank weight is measured. 4 Evaluation Initially the mass difference (m) is determined by weighing the filter before (m 1 ) and after sampling (m 2 ) according to equation (1): m ¼ m 2 m 1 ð1þ The wood dust concentration is calculated according to equation (2): c ¼ m V ð2þ If the optional calcination step is performed and the collected dust that cannot be burned to ash has been determined, then the wood dust concentration is calculated according to equations (3) and (4): m C ¼ m 2C m 1 ð3þ c C ¼ m m C V ¼ m 2 m 2C V where: c is the concentration by weight of the collected dust in the air sample in mg/m 3 c C is the concentration by weight of the collected dust in the air sample in mg/m 3 (after calcination) m 1 is the mass of the filter before loading in mg m 2 is the mass of the loaded filter in mg m is the collected dust on the filter in mg m 2C is the mass of the loaded filter after calcination in mg m C is the part of the collected dust that cannot be burned to ash in mg V is the air sample volume in m 3 ð4þ

7 Wood dust Reliability of the method 5.1 Precision As wood can absorb or emit humidity, depending among other things on its type and origin as well as its storage and treatment, it is impossible to make a generally valid statement on the precision of the entire procedure. In order to estimate the precision of the weighing, laboratory experiments were performed on 5 filters of one type and one size, which were each weighed ten times in the course of a day. The standard deviation of the weighing results for glass fiber filters was 0.06 mg (0.02%) for 70 mm filters and 0.21 mg (0.06%) for 150 mm filters. 5.2 Limit of quantification The limit of quantification depends on the mass of the filters, the equipment used, the state of the equipment and the air sample volume. Under the conditions described here, the absolute and relative limits of quantification were based on the values shown in Table 1. The limit of quantification is calculated as ten times the standard deviation of the difference in weight of at least ten filters (weighing before and after sampling and transport) that were not used for sampling and that were subjected to the entire procedure, including filter treatment, transport to the measurement site and back over a normal processing period (normally from several days to approx. 4 weeks). Internal laboratory tests (e.g. multiple weighing of filters in the course of a day) are not suitable for establishing the limit of quantification, as they result in unrealistically low limits. Table 1 Absolute and relative limits of quantification. Sampling system Filter Flow Air sample Limit of quantification diameter rate volume* absolute relative* [mm] [m 3 /h] [m 3 ] [mg] [mg/m 3 ] VC 25G PM 4G GSP GSP-BIA * For a sampling time of 8 hours

8 202 Analytical Methods The limit of quantification must be checked at regular intervals to detect any errors during storage, transport and weighing. The mass differences between the blank weight and the weight of the filters subjected to the entire handling procedure give indications of systemic errors. 5.3 Selectivity The method is not selective for wood dust. Other types of dust are also included in the mass. The selectivity can be enhanced by determining the part of the collected dust that cannot be burned to ash, as this prevents e.g. the mineral part of the collected dust being taken into account as wood dust. References 1 DIN EN 481 (1993) Workplace atmospheres Size fraction definitions for measurement of airborne particles. Beuth Verlag, Berlin. 2 DIN EN (2002) Workplace atmospheres Assessment of performance of instruments for measurement of airborne particle concentrations. Beuth Verlag, Berlin. 3 DIN EN 143 (2000) Respiratory protective devices Particle filters Requirements, testing, marking. Beuth Verlag, Berlin. 4 VDI guideline 2265 (1980) Determination of the dust concentration in the workplace for industrial hygiene purpose. Beuth Verlag, Berlin. 5 Hebisch, R., Fricke, H.-H., Hahn, J.-U., Lahaniatis, M., Maschmeier, C.-P., Mattenklott, M. (2005) Sampling and determining aerosols and their chemical components. In Deutsche Forschungsgemeinschaft (DFG), Greim, H., Parlar, H. (eds.): The MAK-Collection for Occupational Health and Safety: Air Monitoring Methods, Vol. 9: Wiley-VCH, Weinheim. Author: M. Mattenklott