Annals of Occupational Hygiene Advance Access originally published online on February 2, 2005
Annals of Occupational Hygiene 2005 49(5):439-442; doi:10.1093/annhyg/meh107
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Original Article |
Comparison of Sampling Positions when Measuring Personal Exposure to Solder Fume
Health and Safety Laboratory, Harpur Hill, Buxton, SK17 9JN, UK
* Tel: +44 1298 218518; fax: +44 1298 218570; e-mail: andrew.simpson{at}hsl.gov.uk
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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A sampling device based on a telephone headset was developed and used to support a sampler close to the mouth during personal exposure monitoring of solder fume. In a field trial, it was compared with the established method of mounting the sampler on the arm of a pair of spectacles, and a linear correlation was evident between the two positions (slope 1.56 ± 0.05, r2 = 0.98). Although the headset sampler held the sampler closer to the breathing zone, experience showed that the spectacles position was less intrusive on the subject and allowed a more consistent and stable sampling position. On balance, the spectacles position was the preferred sampling location.
Keywords: breathing zone • resin acids • sampling • solder fume
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Inhalation of rosin-based solder flux fume can cause asthma or worsen an existing asthmatic condition (Burge et al., 1978
, 1980). Consequently, there is a need for a suitable method to measure exposure to solder fume so that adequate control can be demonstrated. As a result of concerns about existing methods for measuring exposure to solder fume, the Health and Safety Laboratory developed a new method for the sampling and analysis of solder fume (Pengelly et al., 1994), published as MDHS 83 (HSE, 1997a). The new method focused on the measurement of the resin acids in the particulate phase of the fume, because these are the major components of the rosin (or colophony) flux in solder and the particulate material emitted. Subsequently, maximum exposure limits (MELs) of 50 µg m–3 (8 h time weighted average) and 150 µg m–3 (15 min short-term limit) for solder fume, measured as total resin acids, have been introduced. An important finding of the earlier work was the recognition of the importance of the position of the personal sampling device to ensure a representative sample. Solder fume tends to be highly directional and rises vertically upwards from the soldering iron tip as a narrow plume. Within this plume, the concentration of fume is very high but at only small distances away the concentration is significantly lower. The amount of fume collected by a personal sampler is therefore critically dependent on its position on the person. The aim of personal sampling is to try to represent what is in the breathing zone. For most occupational hygiene assessments, locating the sampler on the lapel gives acceptable correlation with the breathing zone (Kenny, 2003). Simple observation of persons soldering confirmed that this approach is not appropriate for soldering and could lead to significant undersampling of the fume. In the earlier work (Pengelly et al., 1994), a strategy in which a sampler was placed closer to the mouth and nose by fixing it to the side arm of a pair of safety spectacles was found to collect up to five times as much material as a sampler placed at the traditional lapel position. This was felt to provide a more representative assessment of actual exposure than lapel sampling and became the accepted practice for sampling solder fume (HSE, 1997a). Although this new position for the sampler provided a much better representation of exposure to solder fume than does the lapel, it is clearly possible to place the small sampler used in MDHS 83 even closer to the mouth and nose using a suitable supporting device, such as the microphone arm of a telephone headset. This might be expected to be more representative of the potential exposure. The aim of this work was to compare the sampling position on the side arm of safety spectacles with a location closer to the mouth and nose. |
EQUIPMENT |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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A commercially available headset (Azden HS-35S, from Maplin Professional Services) equipped with a microphone support arm was chosen as the base on which to position the sampler. This headset is light and relatively comfortable to wear and both the adjustable alloy arm and the connection to the headband were sufficiently strong and robust to support the sampling device and tubing. The microphone and accompanying wires were removed and the arm was rotated so that the curved end was moved away from in front of the mouth. The sampler was connected to a 3 mm bore PVC tubing taped to the arm and secured in position with a metal clip. When worn, the tubing was passed over the shoulder to a sampling pump positioned on a belt. The sampler was positioned facing forward,
2.5 cm from the cheek and level with the mouth. In the spectacle method, the sampler faces forward in front of the spectacle frame hinge and the PVC tubing attached to the sampling head is taped to the arm. The method has been described in MDHS 83 (HSE, 1997a). Millipore Swinnex filter holders loaded with 5 µm pore size mixed cellulose ester membrane filters were used to collect the samples at a flow rate of 2 l min–1. The sampling equipment used is illustrated in Figs. 1 and 2.
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EXPERIMENTAL |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Personal exposure measurements were carried out for workers at a site involved in the production of printed circuit boards. Various hand-soldering tasks were carried out using solder containing cores of rosin flux. All subjects were working on tasks which had some form of local extract ventilation. Most workers were positioned next to a fume absorber system to draw the fume away from them onto a charcoal filter; the remaining subjects used soldering irons with tip extraction. This study did not address the relative merits, suitability or effectiveness of these control measures.
Workers undergoing exposure measurements wore both headset- and spectacle-mounted samplers simultaneously, connected to separate sampling pumps. The same type of sampler was used at each position ensuring that the samples collected were directly comparable. The samples collected were stored in sealed tins in a refrigerator prior to analysis by the method described in MDHS 83 (HSE, 1997a). To maximize the number of samples collected for comparative purposes, separate samples were collected before and after the lunch break on different people.
Lapel samples were not included, as previous work has already shown the failings of this position (Pengelly et al., 1994), and an additional sampling pump would have been an unreasonable and impracticable burden under the circumstances of a production environment.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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The participants were generally young in appearance (<40 years old), and only one of the subjects participating was female. When asked to wear both headset and spectacles, subjects in the field trial were initially self-conscious; however, they later reported that both sampling devices were comfortable to wear and that neither was particularly distracting to vision. One subject had the sampler attached to his own personal pair of spectacles. The spectacles appeared to cause less embarrassment than the headset. The two samplers were
10 cm apart, with the sampler on the spectacles protruding 5 cm further forward than the headset sampler when the head was upright. The headset maintained the sampler in position reasonably well during work periods but the subjects removed the sampling equipment during rest breaks and it was not always correctly repositioned (aligning the sampler level with the breathing zone) without assistance. The spectacles did not move out of position, even after replacement after rest breaks. Two of the subjects had long hair but this did not obscure either of the samplers or affect their position. It is conceivable that this may not be the case with all hairstyles. In the uncommon event of solderers wearing respiratory protective equipment it is possible that the headset sampler could be impeded.
The results are summarized in Table 1 and Fig. 3. The cause of the three higher results could not be related to the type of work activity undertaken as each was from a different category (component addition, inspection or modification of the printed circuit boards), but it was noted that the highest result of all was from someone who was sitting somewhat distant from his fume absorber system. Three of the four lowest results were from subjects making modifications. The two lowest results were from subjects using soldering irons with tip extraction.
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The results show that the two sampling positions can produce markedly different results, even though the sampling positions are relatively close to each other. The spectacle position yielded higher exposures, other than at the lowest concentrations where analytical uncertainty was significant (paired t-test: P = 0.016). Although the relative amounts of fume collected at the two sampling positions will be dependent on factors such as posture of the worker and air movement around the soldering iron, Fig. 3 shows a strong correlation between the headset and spectacle positions (slope 1.56 ± 0.05, r2 = 0.98).
The reason for the difference in concentrations is apparent from observation of the posture of subjects during soldering. The plume of solder fume rises vertically from the soldering iron in a relatively narrow column. Operators normally positioned themselves slightly away from the fume with their head inclined downwards, so that the eyes were slightly closer to the fume than the mouth and nose. Perhaps unsurprisingly, the sampler closer to the rising fume collected more sample. What is remarkable is the magnitude of the increase in the sample collected with such a small change in distance. The sampler on the spectacles was only 5–10 cm closer to the plume, yet collected 50% more sample. This study demonstrates the importance of standardizing the appropriate sampler location on the person.
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CONCLUSION |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Both the spectacles and headset sampling methods appear capable of producing exposure data that are representative of actual exposure. Because of the proximity to the mouth and nose, the headset sampling position could be considered to be more likely to yield results closer to the actual exposure. However, the spectacles sampling system is easier and cheaper to construct, is comfortable to wear without causing embarrassment to the user, is relatively less obtrusive and, perhaps of most importance, allows a more stable and reproducible sampling position. Although the spectacles sampling position consistently collects more fume than the nose/mouth position, the data presented here show a linear relationship between the two sets of results, so either position could be acceptable provided this difference is taken into account (the data from this study suggests that a conversion factor of
1.5 could be used to relate solder fume concentrations at the two positions). However, it is important, when measuring exposure to solder fume for comparison with occupational exposure limits, to have a standardized, well-defined and easily reproducible method of capturing the fume because the positioning of the sampler has such a significant effect on the amount of fume collected. Therefore, on balance, the more favourable sampling position for solder fume is on the spectacles. The current maximum exposure limit (MEL) for solder fume based on total resin acids has been set assuming a spectacle sampling position (HSE, 1997b), so all samples collected for comparison with the MEL should ideally be collected using the safety spectacles sampling method. This work highlights the care required when sampling thermal plumes such as solder fume. |
ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Financial and editorial support for this work was provided by the Health and Safety Executive.
Received September 16, 2004; in final form November 4, 2004
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REFERENCES |
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TOPABSTRACTINTRODUCTIONEQUIPMENTEXPERIMENTALRESULTS AND DISCUSSIONCONCLUSIONACKNOWLEDGEMENTSREFERENCES |
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Burge PS, Harries MG, O'Brien IM et al. (1978) Respiratory disease in workers exposed to solder fumes containing colophony (pine resin). Clin. Allergy; 8: 1–14.[CrossRef][Web of Science][Medline]
Burge PS, Harries MG, O'Brien IM et al. (1980) Bronchial provocation studies in workers exposed to fumes of electronic soldering fluxes. Clin. Allergy; 10: 137–49.[CrossRef][Web of Science][Medline]
HSE. (1997a) Resin acids in rosin (colophony) solder flux fume. MDHS 83. HSE Books. ISBN 0717613631.
HSE. (1997b) Rosin-based solder flux fume. Criteria document for an occupational exposure limit. HSE Books. ISBN 0717614417.
Kenny L. (2003) Scientific principles and pragmatic solutions for the measurement of exposure to inhalable dust. Ann Occup Hyg; 47: 437–40.
Pengelly MI, Groves JA, Foster RD et al. (1994) Development of a method for measuring exposure to resin acids in solder fume. Ann Occup Hyg; 38: 765–76.
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