Hand-transmitted vibration in power tools: Accomplishment of standards and users’ perception

Hand-transmitted vibration in power tools: Accomplishment of standards and users’ perception

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  International Journal of Industrial Ergonomics 38 (2008) 652–660 Hand-transmitted vibration in power tools: Accomplishment of standards and users’ perception Margarita Vergara  , Joaquı ´n-Luis Sancho, Pablo Rodrı ´guez, Antonio Pe ´rez-Gonza ´lez a Departamento de Ingenierı´ a Meca´ nica y Construccio´ n, Universitat Jaume I, Campus del Riu Sec, E12071 Castello´ n, Spain Received 21 September 2007; accepted 3 October 2007Available online 19 November 2007 Abstract This work presents the results of the measurements of hand–arm vibration carried out in a field survey. This survey attempted to detectthe main usability problems of handheld power tools in industry.Hand–arm vibration was measured in 70 tools used in different industrial sectors. Ninety workers were interviewed about theirperception of vibration and the symptoms of diseases related with hand vibration.Compliance with current regulations was checked and the relationships between workers’ perception of vibration, measured vibrationlevels and symptoms of vibration-related disorders were analysed.About 15% of the tools exceeded the action limits according to applicable standards. No preventive action was taken in any of thesecases. Furthermore, in most of the cases, workers did not perceive these levels as being too high, which represents an additional risk. Relevance to industry The hand–arm vibration generated by the use of power tools affects over 15% of all workers in industry. r 2007 Elsevier B.V. All rights reserved. Keywords:  Power tools; Hand–arm vibration 1. Introduction This study is a part of a wider research project that isaimed at analysing the problems deriving from the use of power tools in industry. Apart from other issues concern-ing the operators’ safety, one of the main sources of problems usually produced by power tools is the transmis-sion of vibration to the hand and arm.Hand–arm vibration syndrome (HAVS) is a disease thatinvolves circulatory disorders (e.g. vibration white finger),sensory and motor disorders, and musculoskeletal dis-orders, which may occur in workers who use vibratinghandheld tools, in particular pneumatic drills, grinders,electric drills and saws, and jackhammers (Weir andLander, 2005).The relevance of studying hand–arm vibration in powertools for industry is highlighted by a statistical portraitrevealing that 17% of European workers report beingexposed to vibration from handheld tools or machinery forat least half of their working time (European Commission,2002). In the same study, about 13% of workers considerthat their work affects their health in the form of muscularpain in the upper limbs. Only 1% of workers, however,consider that their work affects their health in the form of cardiovascular diseases, although vibration is a well-established risk factor for peripheral circulation impair-ment in the hands (the so-called ‘vibration white finger’).It is probably more difficult for workers to recognise thelink between work-related exposure and cardiovasculardiseases than the work-related risks of musculoskeletaldiseases (European Commission, 2002). A Spanish portraitreveals that 22.8% of the workers that use portable electricand pneumatic tools report being exposed to vibration(INSHT, 1997). ARTICLE IN PRESS www.elsevier.com/locate/ergon0169-8141/$-see front matter r 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.ergon.2007.10.014  Corresponding author. Tel.: +34964728121; fax: +34964728106. E-mail address:  vergara@emc.uji.es (M. Vergara).  To protect workers from developing HAVS, a number of criteria have been proposed in different countries. Inparticular, the European Union (EU) adopted its HumanVibration Directive on April 5, 2002. This directive(Directive 2002/44/EC, 2002) establishes guidelines withrespect to human exposure to hand–arm and whole-bodyvibration that recommend threshold values for occupa-tional exposure to vibration and have now become law inthe member nations of the EU.Important sources in this respect are the Hand–ArmVibration Database developed by the Swedish NationalInstitute for Working Life (NIWF, 2006) and the OPERCdatabase (HAVTEC-OPERC, 2007), which contain field-measured vibration levels registered on the handle of powertools in actual working conditions in accordance with ISO5349 (2001). This information could be used to estimate themaximum recommended time a worker should spend usingthese tools, according to the threshold limit valuesrecommended by the EU. A number of studies haveattempted to determine the real effects of these limits onthe appearance of HAVS in specific sectors such asconstruction (Edwards and Holt, 2006), forestry (Sutinen et al., 2006) or a heavy engineering production workshop(Burstrom et al., 2006), with results that seem to suggestthat, although the prevalence of HAVS is reduced, theaction level currently established in the EU is not a safeone.This work offers the findings from a field study of a wideassortment of tools (saws, drills, grinders, sanders,hammers, etc.) in different sectors such as construction,metal, timber, gardening, maintenance, automotive,etc. The purpose of this study was twofold. On the onehand, it sought to check whether current EU regulationswere being complied with. On the other hand, the aim wasto analyse workers’ perception of vibration, and therelationships between workers’ perception of vibration,measured vibration levels and the existence of HAVSsymptoms. 2. European regulations concerning vibration transmitted bypower tools European Directive 2002/44/EC establishes the mini-mum health and safety requirements regarding theexposure of workers to the risks arising from vibration,and states that the vibration transmitted to the hand–armsystem is to be measured in accordance with the Interna-tional Standard ISO 5349 (2001). Furthermore, StandardISO 8041 (2005) specifies the requirements to be followedand the tolerance limits for instruments designed tomeasure vibration for the purpose of evaluating humanresponse to such vibrations.International Standard ISO 5349 (2001), which is dividedinto two parts, deals about measuring and evaluatinghuman exposure to hand-transmitted vibration. Thisstandard focuses on establishing the conditions themeasurements should be conducted under and the infor-mation that must be recorded, in order to ensure that theresulting data are coherent and can help to improve safetyin the workplace.Standard ISO 5349 quantifies exposure to vibration fromtwo basic data: the total frequency weighted vibration andthe daily exposure time.The magnitude of the vibration is measured by means of the frequency-weighted root-mean-square (rms) accelera-tion, expressed in m/s 2 (Eq. (1)): a hw  ¼  ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiX i  ð W  hi  a hi  Þ 2 r   , (1)where  a hw  is the value of the frequency-weighted rmsacceleration,  W  hi   is the weighting factor for the one-thirdoctave band  i   and  a hi   is the rms acceleration for the one-third octave band  i  .The Standard ISO 5349 establishes the weighting curve,and contemplates a different weighting factor ( W  hi  ) foreach one-third octave band between 8 and 1250Hz.The total value of the frequency-weighted rms accelera-tion is obtained by adding the effects of the frequency-weighted vibration along the three axes ( x ,  y ,  z ) in thebasicentric system defined in Standard ISO 5349 (part 1): a hv  ¼  ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi a 2 hwx  þ  a 2 hwy  þ  a 2 hwz q   , (2)where the root terms represent the frequency-weighted rmsaccelerations in the direction of each axis.The total frequency-weighted acceleration (Eq. (2)) of each daily operation and the exposure time per operationare used to define the 8-h energy equivalent daily exposure A (8) as follows: A ð 8 Þ ¼  ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 T  o X ni  ¼ 1 a 2 hvi  T  i  s   , (3)where  a hvi   is the total value of weighted vibration foroperation  i  ,  n  is the number of different operationsinvolving exposure to vibration,  T  i   is the exposure timefor operation  i   and  T  o  is the 8h reference time (480min or28,800s).Article 3 of Directive 2002/44/EC establishes thefollowing safety limits for  A (8):   exposure limit value (ELV)  ¼  5m/s 2 and   exposure action value (EAV)  ¼  2.5m/s 2 .The ELV is the maximum amount of vibration anemployee may be exposed to in any single day. It representsa high risk above which employees should not be exposed.The EAV is the daily amount of vibration exposure abovewhich employers are required to take action to reduceexposure or to provide regular health checks for theworkers involved.With respect to tools that must be held in both hands,the directive states that measurements should be performedon the two hands and the highest value is then the one thatis taken into account. ARTICLE IN PRESS M. Vergara et al. / International Journal of Industrial Ergonomics 38 (2008) 652–660  653  3. Material and methods This work was part of a much broader study (216interviews, 191 tools, 90 subjects, 42 companies from avariety of sectors such as construction, metal, timber,gardening, maintenance, automotive, etc.) conducted togather data concerning different aspects of power toolsusability, such as noise, safety and vibration. Measure-ments of the vibration transmitted to the hand–arm systemwere performed in 70 tools in 19 companies and 30workers. Each worker was interviewed about the tool ortools he usually works with and the vibration was alsomeasured for the same tool or tools while performing themost representative task. One measurement was performedper tool. The number of each type of tool for whichvibration measurements were carried out can be seen inTable 1, as well as the number of interviews per type of tool. As the task performed with a tool has a greatinfluence on the vibration levels (NIWF, 2006), the toolshave been grouped by the task performed with them, sothat, for instance, grinders used for a task similar topolishing have been grouped with polishers and sanders,while grinders used for cutting materials have beengrouped with circular saws.The vibration transmitted to the hand–arm system wasmeasured using a triaxial accelerometer, and the signal wasrecorded with a MAESTRO human vibration meter(01dB-Stell), which complies with the specifications of the standards ISO 8041 and ISO 5349. The measurementmethod did not fully comply with ISO 5349, as theaccelerometer was attached to the user’s index finger bymeans of a strap in nearly all cases so that on someoccasions measurement was performed on the middle andring fingers. It was placed close to the knuckle (Fig. 1) onthe hand that the operator uses to hold the tool. The mainreason for this discordance was the extent of the study.Since the aim was to further our knowledge of theproblems of using power tools in industry, the exactmodels of the tools were not known until the interviewtook place and a wide diversity of tools could be expected.All four ways of mounting accelerometers on tools statedby ISO 5349 presented problems due to factors such as theneed to modify the tools, previous knowledge of the exactshape of the gripping zone, etc. Furthermore, mounting theaccelerometer on the tool handle close to the hand grip,following the standard procedure, may in some cases affectthe normal use of the tool for the task being analysed. Inaddition, DC-shift may also occur when measurements aremade following the standard for some tools (Griffin, 1990;ISO 5349-2, 2001; Smeatham et al., 2004; Maeda and Dong, 2004). Although mechanical filters can be used toreduce this problem, in some cases they may increase it, e.g.if DC-shift is a problem along a non-dominant axis of apercussive power tool (ISO 5349-2, 2001). We, therefore,looked for a robust method that allowed us to avoid DC-shift and which would be valid for measurements on anypower tool in the study. Taking into account that vibrationtransmissibility at the knuckles has been found to be nearunity at frequencies below 100Hz (Sorensson and Lund-stro ¨m, 1992; Sorensson and Burstro ¨m, 1997), that ISOacceleration weighting at more than 100Hz is very small,and that DC-shift can be avoided by mounting theaccelerometer on the hand (Maeda and Dong, 2004), wedecided to measure vibration by mounting the acceler-ometer on the fingers, close to the knuckles. The adapterthat was chosen for mounting the accelerometer wassimilar to the one used by other authors (Dong et al.,2003, 2005). When the tool was held in both hands, two measure-ments were performed—one in each hand. In accordancewith the standards, the data used in this study are thosecorresponding to the highest vibration. All the recordings ARTICLE IN PRESS Table 1Number of tools used in the studyMeasurement of vibration InterviewsElectricallypoweredPneumaticallypoweredTotalSaw (sabre, jig) 3 4 7 21Hammer (demolition,rotary)2 3 5 12Driller 11 0 11 31Sander, polisher, grinder 12 4 16 35Grinder/saw (cuttinggrinder, circular saw)5 0 5 29Nailer, stapler 0 5 5 17Screwdriver, wrenches 2 9 11 30Router, straight grinders 4 1 5 17Chain saw, hedge trimmer 0 0 0 6Others 2 3 5 18Total 41 29 70 216Fig. 1. Position of the accelerometer during measurement of the vibrationthe tool transmits to the hand. M. Vergara et al. / International Journal of Industrial Ergonomics 38 (2008) 652–660 654  were carried out in compliance with standards ISO 5349-1:2001 and ISO 5349-2:2001, except for the mounting of  the accelerometer, for the reasons we have explainedabove. The measurement was undertaken with the workerperforming the most common task with the tool over arepresentative period of time. The levels of vibration alongthe three perpendicular axes of the accelerometer ( a hwx , a hwy ,  a hwz ) were recorded for each measurement and thesedata were then used to obtain the equivalent globalacceleration ( a hv ).Daily exposures  A (8) were estimated with Eq. (3)from the measured values and the data provided by theworkers about the mean (usual) and maximum daily usagetime of the tool under analysis and then used to determinethe extent of compliance with the regulations. Thecalculation was performed taking into account themost favourable case, i.e. it was assumed that the workeronly used the tool that was being analysed and noothers.Data were also collected about aspects of the tools thatcan have some effect on the transmission of the vibrationto the hand–arm system, such as weight, handle features,and so forth, and the conditions under which the work iscarried out (gloves, extreme temperatures, etc.) in order tobe able to investigate any possible relationships.Lastly, the workers were asked whether they felt thelevel of vibration to be excessive, their overall opinion of the tool (three levels: excellent, normal, poor) andwhether any of them had any characteristic HAVSsymptoms (tingling, numbness, paleness in the hands,diagnosed white finger syndrome) and, if so, whereaboutsin the hand. 4. Results and discussion 4.1. Transmitted vibration Values of   a hv  (in m/s 2 ) vary from 0.33 to 23.56m/s 2 (mean 5.00 and S.D. 5.06m/s 2 ). A box-whisker graphshowing spreads of vibration values  a hv  for each type of tool is presented in Fig. 2. More detailed data, includingunweighted accelerations, are presented in Table 2.Significant differences are observed for the vibration levelsbetween tool types (  p o 0.001). The data recorded generallyagree with what is to be expected for each tool, accordingto NIWF (2006), except for the group of screwdrivers andwrenches for which greater values have been measured(values from NIWF (2006) are 2.96m/s 2 mean, and6.9m/s 2 maximum), maybe due to the tasks or industrialsectors in our study. On the other hand, values are highlydispersed for some types of tools, such as hammers, saws ordrills. This suggests that it would be possible to design orselect tools that transmit lower levels of vibration.A slight correlation is obtained between the vibrationlevels and the tool weight (Pearson correlation coefficient0.24,  p o 0.05), and hence no clear conclusion can be drawn.The correlation between  a hv  and the material anddiameter of the handle was also studied. Although thetools present very different handle materials and diameters,no clear relation is observed. 4.2. Fulfilment of regulations Daily exposure values of   A (8) (in m/s 2 ) calculated from a hv  and the mean daily time of usage vary from 0.05 to ARTICLE IN PRESS Fig. 2. Box-whisker graph showing spreads of vibration values  a hv  for each type of tool. Boxes represent quartiles (25th and 75th percentiles), the thick linein a box represents the median, error bars represent outliers (minimum and maximum values under 1.5 box length) and  1  represents extreme values (valuesbetween 1.5 and 3 box lengths). M. Vergara et al. / International Journal of Industrial Ergonomics 38 (2008) 652–660  655  8.20m/s 2 (mean 1.13 and S.D. 1.49m/s 2 ). A box-whiskergraph showing spreads of   A (8) according to the type of toolis presented in Fig. 3.Seven of the seventy measurements performedexceed the EAV, and three of them even exceed the ELV.Corrective steps were not being taken in any of the cases inwhich the EAV was exceeded. A detailed description of these cases is shown in Table 3. Furthermore, 22 of the70 measurements performed exceed the level of 1m/s 2 for  A (8), a level for which it is advisable to be awareof the risk and to take precautionary steps (Councildirective 89/391/EEC, 1989), according to the PhysicalAgent Directive. ARTICLE IN PRESS Table 2Statistical data for weighted ( a hv ) and unweighted ( a h ) accelerations by type of tool a hv  (m/s 2 )  a h  (m/s 2 )Mean (S.D.) Range Mean (S.D.) RangeSaw (sabre, jig) 10.92 (6.39) 2.1–20 30.53 (12.70) 17–52.4Hammer (demolition, rotary) 15.09 (7.21) 8.8–23.6 50.31 (26.41) 25.3–87.9Driller 5.10 (3.74) 0.6–11.5 16.12 (12.28) 1.7–39Sander, polisher, grinder 2.76 (2.17) 0.9–7.4 13.87 (13.09) 3.3–50.2Grinder/saw (cutting grinder, circular saw) 3.13 (1.33) 1.7–5.1 18.03 (9.31) 8.8–33Nailer, stapler 3.37 (1.38) 1.1–4.5 9.44 (5.72) 2.5–16.6Screwdriver, wrenches 4.90 (2.73) 1.4–10.4 13.86 (7.07) 5–24.6Routers, straight grinders 1.28 (0.75) 0.3–2.3 9.03 (7.62) 2.6–21.8Others 1.04 (0.34) 0.7–1.6 8.65 (6.13) 2.4–16.7All tools 5.00 (5.06) 0.3–23.6 17.75 (15.80) 1.7–87.9S.D., standard deviation; range, minimum–maximum.Fig. 3. Box-whisker graph showing spreads of daily exposure values  A (8) (for the hand that gave the highest value) for each type of tool. Boxes representquartiles (25th and 75th percentiles), the thick line in a box represents the median, error bars represent outliers (minimum and maximum values under 1.5box length) and  1 /* represent extreme values ( 1  for values between 1.5 and 3 box lengths and * for values of more than 3 box lengths).Table 3Detailed description of the measurements that exceeded the EAV A (8) Tool type Mean daily timeof use (min) a hv 8.20 Screwdriver, wrenches 300 10.375.87 Driller 180 9.585.80 Sander, polisher, grinder 300 7.344.51 Sander, polisher, grinder 180 7.363.81 Hammer (demolition,rotary)14 22.322.65 Screwdriver, wrenches 60 7.492.51 Hammer (demolition,rotary)39 8.79 M. Vergara et al. / International Journal of Industrial Ergonomics 38 (2008) 652–660 656
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