Annals of Occupational Hygiene Advance Access originally published online on September 23, 2004
Annals of Occupational Hygiene 2004 48(7):607-615; doi:10.1093/annhyg/meh060
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© British Occupational Hygiene Society Published by Oxford University Press;
Gloves and Dermal Exposure to Chemicals: Proposals for Evaluating Workplace Effectiveness
1 Institute of Occupational Medicine, Research Park North, Riccarton Edinburgh EH14 4AP, UK; 2 University of Aberdeen, Department of Environmental and Occupational Medicine, Foresterhill Road, Aberdeen AB25 2ZP, UK; 3 TNO Chemistry, Chemical Exposure Assessment, PO Box 360, Zeist 3700 AJ, The Netherlands
* E-mail: john.cherrie{at}IOMHQ.org.uk
Received 9 December 2003; in final form 28 May 2004
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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There are standardized laboratory tests for chemical protective gloves that provide estimates of breakthrough time and steady-state permeation flux. However, there is evidence to suggest that these tests may not be completely relevant to glove usage in the workplace. There is no consensus about how glove workplace effectiveness should be assessed, although a few studies have attempted to measure the effectiveness of chemical protective gloves. We have used a conceptual model of dermal exposure to help analyse how workers' skin may become exposed while wearing gloves, and propose a new glove workplace protection factor (PFgloves), which is based on the ratio of the estimated uptake of chemicals through the hands without gloves to the uptake through the hands while wearing protective gloves. Mathematical simulations demonstrate that glove protection factor is unlikely to be constant for a glove type, but will be strongly influenced by the work situation and the duration of the exposure. This has important consequences for the selection of protective gloves.
Keywords: chemical protective gloves • workplace protection factor (WPF)
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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In many workplace situations chemical protective gloves are intended to limit the systemic uptake of chemicals through the skin. There are standardized laboratory tests available to evaluate the permeation of chemicals through glove material (BSI, 1994
; ASTM, 1999) and most manufacturers now publish data on permeation breakthrough time and steady-state permeation flux for their products. However, there are doubts about how well these standardized tests reflect real use conditions. Klingner and Boeniger (2002) highlight five limitations of current laboratory tests:
- Permeation through gloves of mixtures used in the workplace may be different from pure compounds used in the laboratory tests.
- The test of the permeation is generally carried out at lower than skin temperature and permeation may increase with temperature.
- Pressure, stretching and abrasion of gloves in real-life situations may degrade performance.
- Gloves may be reused and this may affect the acceptable use time.
- Manufacturing tolerances mean that different batches of gloves from the same manufacturer may show considerable variation in permeation characteristics.
It is important, however, to differentiate between laboratory-based determinations of performance parameters such as permeation rate or breakthrough time, which are necessary for the purpose of production, certification and selection, and the actual level of protection provided to users of skin protective equipment in real-life exposure scenarios. While the former relates primarily to design and quality control at the production stage, the latter concerns the practical usage of the device. For example, there is good anecdotal information that users do not always wear their gloves continuously. Furthermore, removing and replacing gloves may potentially contaminate the inside of the gloves, leading to additional exposure. Contaminant chemicals may also bypass the glove barrier and flow between the glove and the skin, e.g. a liquid splash to the forearm may run down the arm and inside the glove. This is particularly true when short, wrist-length gloves are employed instead of gauntlets when the hand may be immersed in liquids. Finally, gloves may become cut or punctured and this can result in chemical flowing through the breach onto the skin. It is uncertain how important each of these processes is in reality, or overall how effective gloves are in protecting the hands during work activities.
The workplace effectiveness of respiratory protection has been investigated by measuring the ratio of the contaminant concentration outside the respirator and the corresponding concentration inside the respirator facepiece, i.e. the workplace protection factor (WPF). Measurement of the workplace effectiveness of skin protective equipment is far less well developed than the corresponding techniques used for inhalation exposure, and there have been very few assessments of the workplace effectiveness of gloves. Popendorf et al. (1995) used data from a study of exposure of people applying antimicrobial pesticides to assess the protective effect of gloves worn during the work. Dermal contamination was measured with cotton gloves either worn under the protective gloves, if worn, or otherwise on the hands. Their study was not primarily designed to assess the protection afforded by gloves, and the authors made their assessment by comparing the contamination experienced by those who wore gloves with those who did not, i.e. the ratio of the geometric mean mass of biocide on the gloves from people not wearing protective gloves to the corresponding data from those who wore protective gloves. The mean ratio was 290 for those pouring and/or pumping liquid biocide and 155 for those handling solid biocide powders or flakes. However, the instructions for use of these products specified the wearing of protective gloves and 
95% of the operators chose to comply with the instruction. As such, there were only four workers who did not wear protective gloves compared with 29 who wore the gloves.
Creely and Cherrie (2001) devised a novel approach to measure the contamination of a biocide containing permethrin, inside and outside protective gloves. A pre-washed cotton sampling glove was worn on the outside of a protective glove and another cotton sampling glove was worn underneath the protective glove on the opposite hand. Halfway through the exposure period the arrangement was reversed. The experiments were carried out with three different glove types, all of which were impervious to the biocide over the duration of the tests. The protection was estimated by calculating the ratio of the average mass of permethrin sampled on the outside of the protective glove to the mass sampled inside the gloves.
The geometric mean ratios of the mass of permethrin outside the gloves to that inside were 470 and 200 for two nitrile gloves tested and 96 for the PVC gloves tested. The authors suggested that the lower protection for the PVC gloves was because they were thicker and shorter than the nitrile gloves. Although the test circumstances were standardized there were a number of occasions where the biocide spray equipment failed and this resulted in much lower protection factors (geometric mean ratio 32). Also, in circumstances when the equipment functioned correctly there were clear differences in protection because of operator behaviour (geometric mean ratio 450 for careful workers and 220 for those who took less care). It was suggested that the greater thickness of the PVC gloves meant they were more likely to be removed to complete tasks, and they were also judged to be more susceptible to the biocide bypassing the glove barrier via the short cuff.
Klingner and Boeniger (2002) describe the results of an assessment of different glove type protection among a group of workers handling methylene dianiline (MDA). The workers had been using 0.47 mm thick natural rubber gloves and the study aimed to assess the relative protection afforded by five alternative glove types or combinations of gloves, i.e. two different protective gloves worn one over the other. The exposure was either assessed by biological monitoring (urine) or with cotton sampling gloves worn under the protective gloves.
These authors were surprised to find that there was no apparent advantage in using thicker or more chemically resistant gloves when compared to the original natural rubber gloves. After interviewing the workers they found that they often removed the more protective gloves when they required greater tactile sensitivity to complete a task. It was judged that this caused the MDA to be transferred inside the glove when it was reused. The workers were then trained to recognize the importance of wearing gloves in contaminated areas and a new double glove strategy was introduced: thin natural rubber gloves were worn all of the time and a copolymer laminate glove (type 4H) was worn in contaminated work areas. This new regime resulted in an 80% reduction in exposure as assessed by the biological monitoring results.
Clearly, a number of different approaches have been used to assess workplace effectiveness and it is unclear whether these methods give comparable evaluations, and if they are not equivalent, which approach is most appropriate. In this paper we use a conceptual model of dermal exposure to help define the workplace protection factor for gloves. We use this definition to explore the implications for testing the effectiveness of gloves.
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A CONCEPTUAL MODEL OF DERMAL EXPOSURE AND PROTECTION |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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Schneider and a group of other European researchers have devised a conceptual model of dermal exposure (Schneider et al., 1999
). This describes the processes and ‘compartments’ involved: from the source of the hazardous chemical in the workplace through to permeation of the chemical through the outer skin layers, i.e. uptake. This section briefly describes their model and uses it to provide some insight into the protection provided by gloves.
Uptake of the chemical into the body is mediated by diffusion across the stratum corneum and for this to occur the chemical must be within the ‘skin contamination layer’, a liquid layer in contact with the stratum corneum. The skin contaminant layer should therefore be considered as the contact volume. Diffusion will cause an uptake flux of the chemical if there is a difference in concentration between the skin contamination layer and the peripheral blood flow or extracellular fluids. At steady state the flux is described by Fick's law of diffusion:
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For systemic effects, the mass of contaminant taken into the body will play an important role in determining the consequent risk and so we assume that the most appropriate measure of exposure is the product of exposure concentration, i.e. the concentration in the skin contamination layer (Csk), the area exposed (ASk) and the duration of exposure (tsk), so Esk—the dermal exposure—is:
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Note, we also assume that the flux is the same across the whole skin area exposed, although there are large differences in flux rate between different anatomical locations and even between palmar and dorsal surfaces. This simplifying assumption is made because we are primarily interested in exposure, i.e. at the exterior of the contact surface, rather than internal body burden. We assume differences in actual uptake because of the location of exposure on the body should be taken account in a risk assessment as part of the evaluation of the dose received by the individual. However, it is less important in assessing the effectiveness of gloves.
These equations are also only valid if there is an excess supply of the contaminant available for uptake. If this is not the case, then the mass of the contaminant chemical in the skin contaminant layer (Msk), minus any losses from evaporation or cleaning, would be equal to the uptake. Mathematically, if kp · Esk > Msk, then Usk = Msk, otherwise Usk = kp · Esk. From this we can see that the uptake is the most relevant exposure-related metric for the assessment of risk and hence glove effectiveness.
The model of Schneider and his co-workers comprises compartments, such as the skin contamination layer, and transport processes that allow the contaminant mass to move from one compartment to another (Schneider et al., 1999). The skin contamination layer is on the skin surface and the uptake is the transport through the stratum corneum. It should be stressed that the model focuses on the processes at a conceptual level to help analyse the way in which people may become exposed and it is not intended to provide a basis on which to predict exposure.
Two compartments in the model relate to the indoor environment where exposure takes place: the room air and the internal surfaces. There are two compartments for clothing, which includes gloves, and in the remainder of this paper we will refer specifically to gloves in relation to clothing. The first of these two compartments represents the outer surface of the gloves and the second one the inner surface of the gloves. Flow between the two compartments is regulated by a permeation barrier, i.e. the glove material, and then onto the skin contamination layer. However, it is clear that this is not the only way that contamination can get into the skin contamination layer from the outside since there are transport processes between the outside of the gloves and the skin or directly onto the skin from the source or other compartments. A full description of each of the compartments and transport processes is given in Schneider et al. (1999).
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THE IMPACT OF GLOVES ON UPTAKE THROUGH THE SKIN |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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In the workplace the wearing of gloves may have important consequences for dermal uptake. If someone is handling a liquid chemical without any gloves, then a splash of the liquid or immersion of the hand in the chemical may completely overwhelm the skin contamination layer so that the liquid chemical essentially comprises the skin contamination layer. If the material is undiluted, then uptake will proceed rapidly as there will be a large concentration difference between the skin contamination layer and the peripheral blood supply, as indicated by equations (2) and (3). Conversely, if the contaminant material is in a dilute form, there will be relatively slow uptake.
However, if the person is wearing a glove the situation will be different. Assuming the chemical only comes into contact with the outer glove surface, there will be no flux into the inner glove contamination layer until the chemical breaks through. Thereafter there will be, in an ideal situation with a large external reservoir of contaminant, a steady flux of chemical into the inner surface compartment. The chemical must first partition into the glove and then diffuse towards the inner glove surface; then it must partition into the skin contamination layer. There is no possibility of the sweat layer being washed away by the diffusive flux and so the maximum concentration that can be achieved in the sweat will be the saturated water concentration for that chemical. Diffusion through the stratum corneum is then dependent on this concentration, which if the worker is handling the chemical in a concentrated form is likely to be much less than is present on the outer surface of the glove. Therefore, the flux through the glove will ultimately be limited by the flux through the skin from a saturated water concentration; in some situations the glove permeation rate may be the determinant of the flux through the skin, but only if this is less than the flux from the saturated water solution.
We explore the consequences of this model in a hypothetical work scenario. In an aircraft factory nitrile rubber gloves are used to protect the hands of a worker who cleans components with toluene. The work is done inside a fume cupboard to control inhalation exposure. The worker takes 60 min to complete the task and throughout this time the palms of her gloves are covered with toluene. At the end of this work the gloves are removed and placed in a waste container.
The dermal uptake that might occur if no gloves were worn can be estimated from the work of Kezic et al. (2001) who exposed volunteers to a range of solvents over a 27 cm2 area on the forearm for 3 min. The experimental conditions were carefully controlled so that it was impossible to inhale toluene during the test, and the toluene vapour in the expired air was then measured for 1 h after exposure. The dermal toluene flux was calculated from comparative data for the exhaled toluene concentrations resulting from inhalation exposure, with the assumption that regardless of the route of exposure, for the same toluene mass uptake the concentration in expired air would be the same. The permeation rate of toluene averaged over the exposure period was 1.2 mg/cm2/h. The results from such a short exposure period are perhaps not representative of the steady-state diffusion conditions that would occur in a longer exposure scenario, and the palm will be less permeable to toluene than the forearm. Nevertheless, these data provide some basis to estimate the risk from uncontrolled work. If it is assumed that gloves are not worn, then 500 cm2 of the hands are exposed for 60 min, resulting in an uptake of 600 mg, which is quite a substantial contribution to this worker's risk. For example, someone inhaling toluene vapour throughout this task at the level permitted in the UK (191 mg/m3) and a breathing rate of 0.025 m3/min would inhale 286 mg.
Data from the glove manufacturer suggest that the breakthrough time for the nitrile gloves is 45 min and the steady-state flux in a standardized laboratory test system is 8.3 mg/cm2/h. If we assume there is no uptake until breakthrough and then the flux through the glove and skin corresponds to the steady-state value quoted by the manufacturer, then the uptake would be 1040 mg, i.e. [8.3 x 500 x (60 – 45)/60]. This is greater than we might expect without protection and so seems an implausible basis on which to assess risk. In this case the skin provides better resistance to toluene permeation than the glove. This is unsurprising since the laboratory test is not designed to mimic in-use conditions.
Boeniger and Klinger (2002) report the results of in vivo laboratory experiments carried out by Boman and colleagues to investigate the protection afforded by gloves. They found that even for highly permeable glove membranes, where the permeation rate reported by the manufacturer exceeded the skin absorption rate, a reduction in uptake was seen when the membrane covered the skin. For example, the glove permeation rate in an in vitro test system was measured as 18 mg/cm2/h, whereas the permeation rate through the glove on miniature pig skin was only 0.3 mg/cm2/h. The authors speculate that the aqueous layer under the glove may reduce the concentration gradient between the stratum corneum and the subcutaneous tissues because of the necessity for the toluene to dissolve in the sweat.
It may therefore be more appropriate, and a more reliable basis to assess uptake, if we assume that the highest toluene concentration that could be in the skin contamination layer under a glove is the saturated water concentration (515 mg/l). The uptake can then be estimated using the software program SKINPERM (developed by Will ten Berge: http://home.planet.nl/~wtberge/skinperm.html), which has been developed as a general-purpose tool to estimate uptake in this type of situation. The predicted uptake flux is 0.02 mg/cm2/h and the predicted uptake, again for the last 15 min of the task, would be 2.5 mg.
We propose that the protection factor provided by gloves should be assessed by comparing the estimated mass uptake of the chemical through the skin when no protection is worn (Usk,hands) with the uptake while the gloves are worn (Usk,gloves). By analogy with the approach used for respirators, we can calculate the protection factor for the gloves (PFgloves) as the ratio of these two uptake values. In this way the protection factor correctly indicates the reduction in risk that might be expected from wearing gloves.
 | (4) |
For the toluene scenario outlined above, the estimated protection factor is 240. However, it might be expected that if the task took longer than 60 min the protection factor would be lower than this value, and if it was shorter the protection factor would be higher. If the gloves are worn throughout the task, then the value of PFgloves will tend towards the ratio of the flux through the skin without gloves and the flux through the skin when the gloves are worn; in this case PFgloves would be 60.
The above analysis assumes that the only way in which the skin inside the glove may become contaminated is by diffusion through the glove. However, as we have seen it is also possible for chemicals to be introduced inside the glove through the gap between the wrist and the glove cuff. In the hypothetical cleaning task using toluene, if we assume that on average every 15 min a splash of liquid of 0.1 ml (87 mg of toluene) lands inside the gloves and spreads to cover 5 cm2, then we can estimate the uptake by this route as 1.5 mg over 15 min. The estimate is based on the uptake rate for pure toluene, i.e. 1.2 mg/cm2/h. This, of course, assumes that the uptake is the same as we have assumed when the hand is not occluded by the glove and that the toluene does not all evaporate, both of which seem reasonable assumptions. Note that most of the toluene from splashes will remain inside the glove after a splash and will eventually be lost to the air by evaporation, either while the glove is worn or more likely after it is removed.
Figure 1 shows the protection factor for this scenario, assuming either that there is splashing of pure toluene inside the glove or that low concentration of toluene is splashed into the glove (giving rise to an uptake flux of one-tenth that of pure toluene). The graph shows the change in protection factor for task duration between about 20 min and 2 h, with the protection factor being 10–100 times greater for the low-concentration material. It is clear from this graph that in this scenario the glove breakthrough time has little relevance to the degree of protection provided and the protection factor decreases steadily as the task continues. This type of pattern is probably always going to arise when there is a significant reduction in the efficacy of gloves because of contamination bypassing the glove barrier. The dependence of glove protection factor on the duration of the task is very different from respirators where it is assumed that the protection factor is constant and independent of the concentration of contaminant challenging the device.
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Figure 2 compares the hypothetical protection for the original nitrile glove and an alternative Viton glove. The manufacturer's data suggest that the Viton gloves have a breakthrough time of 240 min and so we have assumed the task lasts up to 8 h to illustrate the relative difference in performance of the two glove types. The steady-state flux of toluene through the glove after breakthrough is quoted as 4.1 mg/cm2/h. Before breakthrough of the nitrile gloves, both types of glove give identical protection, thereafter the protection factor of the nitrile gloves decreases rapidly and there is about a 4–5 times greater protection factor from the Viton gloves. The performances of the nitrile and Viton gloves come closer to each other after toluene breakthrough with the Viton gloves.
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IMPLICATIONS FOR TESTING THE EFFECTIVENESS OF GLOVES |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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We propose that the most appropriate way to assess the real-life protection afforded by gloves is to undertake a workplace assessment rather than rely on laboratory test data. Our view is that laboratory tests may provide a basis for glove selection but do not provide a realistic indication of the protection afforded in practice. The above arguments suggest some important implications for field testing of glove efficacy.
In a number of cases researchers have tried to assess the permeation of chemicals through gloves in the workplace using adsorbent or absorbent pads located inside gloves. This design may again overestimate the permeation through the glove because the pad will generally provide a more extensive reservoir for permeating chemicals than the skin contamination layer, which is exactly what we saw with the hypothetical example involving toluene described in the previous section. Ideally we need a sampler that more accurately reflects the way that chemicals are taken up through the skin, i.e. a ‘biologically relevant’ sampler (Cherrie and Robertson, 1995), although this type of sampler is still not commercially available.
We have used the toluene cleaning scenario described earlier to explore two possible suggestions for a practical assessment technique:
- Using adsorbent materials over and under the glove, similar to that used by Creely and Cherrie (2001).
- The use of fluorescent tracer to assess the area of glove and the area of hand contaminated.
In each case the protection factor was calculated as the ratio of the outside exposure metric (mass or area) to the inside glove metric. Both alternative approaches were compared with the glove protection factor calculated from the uptake estimates (Fig. 3).
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To estimate the mass of chemical that might be inside the glove we have used the mass of toluene that was notionally splashed inside the glove and assumed that the adsorbent sampling glove was sufficient to retain it all. To that we added the estimated mass flux through the glove assuming that it was not limited by the necessity to dissolve the chemical in water, i.e. we used the flux rate quoted by the manufacturer on the assumption that the adsorbent in the inner sampling glove would sustain the higher permeation rate. For the external exposure we have assumed that a 1 µm layer of toluene would come into contact with the exposed outer glove surface every 5 min. It is difficult to judge exactly how much toluene would be in contact with the hand and so this choice is rather arbitrary.
For the area exposed under the glove we have used the same assumptions involved in the calculation of uptake, although we did not take into account permeation on the assumption that the fluorescent tracer would not pass through the glove. The outside exposed area was again based on the assumption used in the calculation of uptake. All calculations were made for the nitrile gloves assuming pure toluene was used.
Interestingly all three measures show similar changes in estimated protection factor as the task duration increases, although each graph is systematically displaced from the others. The protection factors differ by approximately an order of magnitude. However, there is no guarantee that, for example, the assessment based on area will always produce the highest estimated protection factor or that the assessment based on the mass will always be lowest. If, for example, the task had been carried out with a material containing a lower concentration of toluene, then the protection factor estimated from uptake would have been much higher, although the protection factor estimated based on area would probably have been comparable to that shown in Fig. 3.
Despite these reservations, it might be possible to use measurements of contaminant mass and surface area exposed to estimate uptake, provided there was additional information about the concentration of the contaminant in the bulk liquid or where an estimate of the uptake flux was available for the substance.
Perhaps the best approach would be to use biological monitoring to evaluate PFgloves. This would necessarily need to be carried out in a semi-experimental study to ensure that the measurements reflected the protection afforded by the gloves and not other influences, e.g. background levels of the material in the body from prior exposure. Workers would need to wear a high level of respiratory protection to ensure that there was no contribution to exposure from inhalation of the contaminant substance. It would be necessary to ensure that it was ethically acceptable to have the work carried out without wearing protective gloves, because the protection factor would be obtained from the level measured without wearing gloves to that while wearing gloves. If we adopted an intervention study design, then it would not be necessary to take account of inter-individual variation in metabolism, sweat rate and other relevant physiological parameters.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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We have outlined current theoretical concepts about dermal exposure and the practical methods that are available to measure the results of exposure. The conceptual model developed by Schneider and his colleagues points towards a logical definition of the ‘workplace protection factor’ for gloves based on the ratio of uptake through the unprotected skin to the corresponding uptake through the hands when protective gloves are worn. Unfortunately, there are currently no standardized methods to measure uptake and so there are real difficulties in assessing workplace glove protection.
Assessment of workplace protection using the mass loading of chemical on the skin and glove surface or other measures of exposure may be undertaken. Strictly speaking, however, the ratio of measurements of the mass or area of skin contamination with and without gloves would indicate a reduction of mass loading or area exposure rather than protection. Our analysis suggests that these tests may give estimates of ‘reduction’ that are systematically biased and that this bias may either be positive or negative. The calculations we have done also incorporate a number of assumptions that may or may not be justified, although we believe they are a reasonable basis for comparing the possible measurement strategies. However, further work is needed to ensure that the conclusions we have arrived at are truly robust.
The concept of protection factor for gloves appears to be quite different from what is often assumed for other personal protective equipment, particularly respirators used to protect the respiratory system. For gloves the protection factor will not be constant either with the duration of exposure or with the concentration of the challenge chemical, both of which are fundamental assumptions for respiratory protection. This means that protection factor is less an intrinsic property of the glove and more a reflection of the exposure scenario and the glove. It is therefore not likely to provide such a simple basis for glove selection as is commonly used for respirator selection.
Furthermore, the concept of breakthrough time may be a less reliable indicator of glove performance in the workplace than we have previously assumed. The current approach for the selection of protective gloves relies on breakthrough time as a primary decision tool on the assumption that gloves provide absolute protection up to that time. However, in our hypothetical calculations there was often little change in the trend of decreasing protection factor with time, either before or after breakthrough. This is because the concept of breakthrough is strongly premised on the assumption that the only route for contaminant onto the hand of someone wearing protective gloves is permeation through the protective layer. This is patently not the case and there may be quite significant quantities of chemical that bypass the glove protective layer. Further research is needed to define the utility of breakthrough time in glove selection.
A central element of our calculations is the assumption that if the hand is exposed to bulk chemical, then this will swamp the skin contamination layer (containing sweat) and uptake through the skin will be dictated by the concentration of the chemical in the bulk liquid. However, if the chemical permeates through the glove we have assumed that the flux is insufficient to overwhelm the skin contamination layer and the chemical must therefore dissolve into the sweat before permeating through the skin. For toluene this meant that the estimated permeation through the glove was lower than the data provided by the glove manufacturer because the flux from a saturated solution of toluene in water was lower. This may not always be the case and for some chemicals it is possible that the flux from a saturated aqueous solution might be equal or greater to the glove permeation rate and so the glove would become the rate-limiting factor for uptake.
The available research on workplace protection from gloves highlights the importance of human behaviour in determining efficacy (Creely and Cherrie, 2001; Klinger and Boeniger, 2002). Removal and replacement of gloves during work will almost certainly compromise the protection to some extent, even if the worker does this carefully. It is also possible that when a person is wearing gloves they have an unrealistic belief that they are absolutely protected and may therefore take less care in coming into contact with chemicals compared with when they are not wearing gloves. For example, if someone dropped a component into a bath of metalworking fluid, they might use a long wire to retrieve the item, whereas if they were wearing gloves they might just plunge their hand in to get the component. This behaviour modification may give an erroneous impression of the actual reduction in exposure that might be achieved with the use of gloves.
The overall conclusion of our analysis is that measurement of workplace glove protection factor is practicable and we believe this type of study should be undertaken more widely. The most appropriate strategies that are currently available are to use the available measures of exposure to estimate uptake with and without the protective gloves, with the protection factor being the ratio of these uptake measures. A carefully controlled biological monitoring intervention study could also be used to provide a similar estimate of protection factor. Where the protection from gloves is not based on an assessment of uptake, then the data will require careful interpretation and the basis for the evaluation should be clearly stated, for example the reduction of contaminant mass loading. We have argued that it is inappropriate to use the term ‘protection factor’ in these situations.
It is most important that a standard protocol be developed for glove workplace protection studies. This protocol should provide guidance on the conduct of studies, plus the estimation of protection factors and other measures of glove protection. In this way we can ensure that any data that are obtained in the future will be comparable and can be generalized to other situations. Alongside this protocol there should be a standardized terminology for studies of the protection afforded by gloves and protective clothing.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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We are grateful to Rob Aitken from IOM who provided constructive comments on the manuscript. The figures are reproduced by permission of CRC Press. The work was partly funded by a grant from the CEFIC Long-range Research Initiative (LRI).
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REFERENCES |
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TOPABSTRACTINTRODUCTIONA CONCEPTUAL MODEL OF...THE IMPACT OF GLOVES...IMPLICATIONS FOR TESTING THE...DISCUSSIONACKNOWLEDGEMENTSREFERENCES |
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ASTM. (1999) Standard test method for resistance of materials to permeation by liquids and gases under conditions of continuous contact. ASTM Method F739-99. West Conshohocken, VA: American Society for Testing and Materials.
Boeniger MF, Klingner TD. (2002) In-use testing and interpretation of chemical-resistant glove performance. Appl Occup Envir Hyg; 17: 368–78.[CrossRef]
BSI. (1994) Protective gloves against chemicals and micro-organisms. Part 3: Determination of resistance to permeation by chemicals. European Standard EN374-3. London: British Standards Institute.
Cherrie JW, Robertson A. (1995) Biologically relevant assessment of dermal exposure. Ann Occup Hyg; 39: 387–92.
Creely KS, Cherrie JW. (2001) A novel method of assessing the effectiveness of protective gloves—results from a pilot study. Ann Occup Hyg; 45: 137–43.
Kezic S, Monster AC, van de Gevel IA, Kruse J, Verberk MM. (2001) Dermal absorption of neat liquid solvents in brief exposures in volunteers. Am Ind Hyg Assoc J; 62: 12–18.
Klingner TD, Boeniger MF. (2002) A critique of assumptions about selecting chemical-resistant gloves: a case for workplace evaluation of glove efficacy. Appl Occup Envir Hyg; 17: 360–7.[CrossRef]
Popendorf W, Selim M, Lewis MQ. (1995) Exposure while applying industrial antimicrobial pesticides. Am Ind Hyg Assoc J; 56: 993–1001.[Web of Science][Medline]
Schneider T, Vermeulen R, Brouwer DH, Cherrie JW, Kromhout H, Fough CL. (1999) Conceptual model for assessment of dermal exposure. Occup Envir Med; 56: 765–73.
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