An optimal sampling approach to modelling whole-body vibration exposure in all-terrain vehicle driving

Abstract

Exposure to whole-body vibration (WBV) presents an occupational health risk and several safety standards obligate to measure WBV. The high cost of direct measurements in large epidemiological studies raises the question of the optimal sampling for estimating WBV exposures given by a large variation in exposure levels in real worksites. This paper presents a new approach to addressing this problem. A daily exposure to WBV was recorded for 9–24 days among 48 all-terrain vehicle drivers. Four data-sets based on root mean squared recordings were obtained from the measurement. The data were modelled using semi-variogram with spectrum analysis and the optimal sampling scheme was derived. The optimum sampling period was 140 min apart. The result was verified and validated in terms of its accuracy and statistical power. Recordings of two to three hours are probably needed to get a sufficiently unbiased daily WBV exposure estimate in real worksites. The developed model is general enough that is applicable to other cumulative exposures or biosignals.

Practitioner Summary: Exposure to whole-body vibration (WBV) presents an occupational health risk and safety standards obligate to measure WBV. However, direct measurements can be expensive. This paper presents a new approach to addressing this problem. The developed model is general enough that is applicable to other cumulative exposures or biosignals.     

The effect of occupational whole-body vibration on standing balance: A systematic review

Adverse health effects from exposure to occupational whole-body vibration (WBV) are common among drivers. In particular some researchers consider that there is kinaesthetic and balance disturbance from WBV exposure in the workplace and this might be one of the aetiological factors responsible for occupational low back pain in drivers. The purpose of this study was to undertake a critical review of the literature to determine whether exposure to seated occupational WBV can affect standing balance performance in an actual or simulated occupational environment. Specific keywords and MeSH terms for three major areas included WBV, balance and occupation. These were used to conduct a systematic search of the following databases; PubMed, EMBASE (Ovid), Medline (Ovid), CINAHL (EBSCO), Academic Search Complete (ASC), AMED, Scopus, Web of Science, Science Direct, Proquest, Cochrane library(OVID), IEEExplore and ProQuest Dissertations and thesis, Google Scholar, WorldCat and related conference proceedings. Five articles met the inclusion criteria and were assessed for quality. Two were field studies conducted on actual vehicles (a long haul freight truck and a bulldozer), while the other three were laboratory studies simulating the characteristics of the following vehicles; long-haul-dump vehicle, underground mine shuttle car, and helicopter. The systematic review scored the methodological quality of the included articles with an average and standard deviation of 76 ±12.3% (range 59- 93%) indicative of high quality. Three of the five studies (two field and one laboratory) found evidence for seated WBV decreasing standing balance performance while two laboratory studies did not find such effects. Thus there is modest evidence to suggest there is a decrease in standing balance performance following exposure to seated occupational WBV.

Relevance to industry

This systematic review suggests that balance deficits may exist immediately following exposure to occupational seated WBV and may predispose driver/operator to low back injury during manual material handling tasks immediately post driving.     

Combined exposures of whole-body vibration and awkward posture: a cross sectional investigation among occupational drivers by means of simultaneous field measurements

Abstract

Objective: Multifactorial workloads such as whole-body vibration (WBV), awkward posture and heavy lifting are potential predictors for low back pain (LBP). In this study, we investigate the association between LBP and these exposures among 102 professional drivers. Methods: The combined exposures of WBV and posture are measured at different workplaces. Health and personal data as well as information about lifting tasks are collected by a questionnaire. Results: The daily vibration exposure value (odds ratio 1.69) and an index for awkward posture (odds ratio 1.63) show significant association with the occurence of LBP. Awkward posture and heavy lifting appear to be more strongly associated with sick leave than WBV exposure. Furthermore, a combination of the measurement results of WBV and awkward posture into one quantity also shows significant correlation to LBP. Conclusion: The combined exposure of WBV and awkward posture can be described in terms of the daily vibration exposure and the index for awkward posture. This facilitates work place assessments and future research in this area.

Practitioner Summary: For the first time, quantitative measures combining whole-body vibration and awkward posture exposures have shown to correlate with the occurrence of low back pain significantly. This validates the proposed quantities and measurement methods, which facilitate workplace assessments and assist in the design of further studies which are necessary to establish a causal exposure–response relationship.     

A survey of expert opinion on the effects of occupational exposures to trunk rotation and whole-body vibration

We present a review of current expert opinion on the effects of combined exposures to trunk rotation and whole-body vibration (WBV), commonly experienced by operators of agricultural machinery. We evaluate the level of agreement between academic experts in the field of ergonomics, human response to WBV and agricultural operators, on the effects of exposure to WBV and trunk rotation. A total of 83 individuals responded to the paper-based questionnaire, which included questions on risk levels from individual and combined exposures, discomfort development, exposure duration limits and tasks within agriculture. The results showed that all groups considered exposure to WBV and trunk rotation as risk factors for the development of back pain. The experts were not in consensus regarding acceptable exposure durations, areas of discomfort experienced or recommendations for cab developments.     

Inter-individual postural variability in seated drivers exposed to whole-body vibration

Long-term occupational exposure to whole-body vibration (WBV) is a cause of low back pain for seated drivers. Poor and long-term seated postures are considered as a cofactor in the risk. It depends on the vehicle's ergonomics and tasks. Differences in posture may also be observed between operators doing identical tasks. An experiment has been performed in order to simultaneously measure posture and WBV for 12 drivers in 3 vehicles (loader, dumper and excavator) during controlled tasks. The inter-individual postural variability has been evaluated. The positions and movements of the body were measured with the CUELA system (computer-assisted recording and long-term analysis of musculoskeletal loads). Significant differences were observed between the three vehicles in the WBV, positions and movements of the body. Significant postural differences were observed between drivers (EN 1005-4 2005). Individual strategies for performing a task were also identified.     

Comparison of whole-body vibration exposures in buses: effects and interactions of bus and seat design

Bus and seat design may be important for the drivers' whole-body vibration (WBV). WBV exposures in buses during actual operation were assessed. WBV attenuation performance between an air-suspension seat and a static pedestal seat in low-floor buses was compared; there were no differences in WBV attenuation between the seats. Air-suspension seat performance in a high-floor and low-floor bus was compared. Relative to the pedestal seat with its relatively static, limited travel seat suspension, the air-suspension seat with its dynamic, longer travel suspension provided little additional benefit. Relative to the measurement collected at the bus floor, the air-suspension seat amplified the WBV exposures in the high-floor bus. All WBV exposures were below European Union (EU) daily exposure action values. The EU Vibration Directive only allows the predominant axis of vibration exposure to be evaluated but a tri-axial vector sum exposure may be more representative of the actual health risks.     

Neck pain combined with arm pain among professional drivers of forest machines and the association with whole-body vibration exposure

The purpose of this study was to investigate the existence of neck pain and arm pain among professional forest machine drivers and to find out if pain were related to their whole-body vibration (WBV) exposure. A self-administered questionnaire was sent to 529 forest machine drivers in northern Sweden and the response was 63%. Two pain groups were formed; 1) neck pain; 2) neck pain combined with arm pain. From WBV exposure data (recent measurements made according to ISO 2631–1, available information from reports) and from the self-administered questionnaire, 14 various WBV exposure/dose measures were calculated for each driver. The prevalence of neck pain reported both for the previous 12 months and for the previous 7 d was 34% and more than half of them reported neck pain combined with pain in one or both arms. Analysis showed no significant association between neck pain and high WBV exposure; however, cases with neck pain more often experienced shocks and jolts in the vehicle as uncomfortable. There was no significant association between the 14 WBV measures and type of neck pain (neck pain vs. neck pain combined with arm pain). It seems as if characteristics of WBV exposure can explain neither existence nor the type of neck pain amongst professional drivers of forest machines. The logging industry is important for several industrialised countries. Drivers of forest machines frequently report neuromusculoskeletal pain from the neck. The type of neck pain is important for the decision of treatment modality and may be associated with exposure characteristics at work.     

Whole body vibration exposures in bus drivers: A comparison between a high-floor coach and a low-floor city bus

Low back pain (LBP) is common in occupational bus drivers and studies have shown a dose–response relationship between whole body vibration (WBV) exposure and LBP. Bus design may be an important factor in determining the WBV exposure a bus driver receives. The purpose of this study was to determine whether differences exist in WBV exposures between two buses commonly used in long urban commuter routes: a high-floor coach and a low-floor city bus. Each bus was driven over a standardized test route which included four road types: a newer smooth freeway, a rougher old freeway, a city street segment, and a road segment containing several speed humps. WBV exposures were calculated per ISO 2631-1 (1997) and ISO 2631-5 (2004) standards. WBV exposures were significantly higher in the high-floor coach bus on the road segment containing speed humps. There were primarily small differences between buses in WBV exposures encountered on the city street and freeway segments. With respect to the ISO 2631-1 and European Union's A(8) and VDV(8) action limit values, both buses could be operated on the smooth freeway without exceeding the 8-hour action limits but would have to be operated less than 8 h when operating on the other road types. On average, the seats only attenuated 10% of the floor transmitted vibration and amplified the vibration exposures on the speed humps. Due to the low vibration attenuation performance of the bus driver's seat, evaluating different types of seats and seat suspensions may be merited.Relevance to industryLow back Pain (LBP) is one of the leading causes for workplace disability; therefore, it would be beneficial for employers and workers to minimize WBV exposures resulting in LBP. To reduce WBV exposures, buses should be assigned to appropriate routes and drivers should rotate across routes to vary continuous and impulsive exposures.     

The impact of different seats and whole-body vibration exposures on truck driver vigilance and discomfort

Laboratory studies have shown that exposure to whole-body vibration (WBV) increases physical and mental fatigue, which are common issues professional drivers face. The objective of this study was to determine whether altering WBV exposures had any effect on driver vigilance and discomfort. A repeated measures crossover design of five truck drivers with regular 10-h routes was used. Active and passive suspension truck seats were evaluated. For each seat, WBV exposures were measured. Participants completed a discomfort questionnaire and a reaction time task before and after their shift for two weeks, one week per seat. Compared with the passive seat, the active seat significantly reduced WBV exposures, decrements in the optimal and mean reaction times (p = 0.02, 0.047, respectively), and discomfort in the lower back and wrist(s)/forearm(s) (p < 0.01, 0.01, respectively). Study results indicated that reducing WBV helps reduce discomfort and maintain vigilance, which may improve drivers’ health and reduce the risk of truck collisions.

Practitioner Summary: The active suspension seat used in this study reduced truck drivers’ exposure to whole-body vibration (WBV) by over 33% in relation to their current industry standard passive suspension seat. This study demonstrated that reducing truck drivers’ exposure to WBV reduced fatigue and discomfort development over a workday.     

Effects of occupational vibration exposure on cognitive/motor performance

Whole-body vibration (WBV) occupational exposure levels were determined with 29 different types of machinery. Two distinct WBV exposure profiles were found and reproduced in a controlled exposure situation that involved the transformation of a vehicle. A sample of 45 volunteer subjects was recruited to assess the effects of WBV on their cognitive/motor performance. Two different tests were selected and applied: an Action Judgment Test, which was primarily designed to examine the relation between the distribution of attention and the resultant reaction to ever-changing conditions, and an Omega Test, designed to examine the precision and attention in handling mechanisms. The results show that the vibration exposure level affects the degree of impairment. The subjects presented a lower performance level when exposed to higher vibration levels, as the time required to correct their errors more than doubled. No significant differences were found when comparing the performance for gender or age variables. The obtained results can be used to improve the characteristics of work vehicles, in order to reduce the corresponding adverse effects and, consequently, improve the corresponding working conditions.     

Postural stability after whole-body vibration exposure

Fall injuries to operators of heavy mobile equipment are more frequent during egress rather than while climbing onto the equipment. One possible contributing factor is a loss of postural stability during egress. Because many of these operators are exposed to prolonged periods of whole-body vibration (WBV) while controlling the equipment, a study was conducted to determine if postural stability is impaired by WBV exposure. Subjects were tested for a difference in standing postural sway before and after seated WBV exposure. The WBV consisted of 40 minutes of vertical vibration generated by a motion platform, which emulated actual vibration levels of an operating under-ground shuttle car. Two independent variables, each at two levels, consisted of vibration and vision. The measured dependent variables were postural sway amplitude and velocity of sway. No significant difference between the vibration and no vibration conditions were found. Based on the results of this study, it cannot be concluded that WBV at the exposed frequencies influences postural stability. The results suggest that other factors may be the primary contributors to fall injuries while exiting the vehicle, such as problems with foot placement accuracy or egress system design.     

Whole body vibration exposures in forklift operators: comparison of a mechanical and air suspension seat

Using a repeated measures design, this study compared differences in whole body vibration (WBV) exposures when 12 forklift operators drove the same forklift with a mechanical suspension and an air suspension seat. A portable PDA-based WBV data acquisition system collected and analysed time-weighted and raw WBV data per ISO 2631-1 and 2631-5 WBV measurement standards. Tri-axial measurements of weighted vibration (A(w)), crest factor, vibration dose values, time-weighted average-peak, raw (+) peak, raw (-) peak and static compression dose (S(ed)) were compared between seats. There were significant differences in z-axis WBV exposures with the air suspension seat, yielding lower WBV exposures. In addition, there were differences between seats in how they attenuated WBV exposures based on the driver's weight. In the mechanical suspension seat, WBV exposures were weight-dependent, with lighter drivers having higher WBV exposures, whereas with the air suspension seat, the same trends were not as prevalent. STATEMENT OF RELEVANCE: This study contributes to the understanding of how different seat suspensions can influence WBV transmission and how some components of vibration transmission are dependent on the weight of the driver. Additional systematic studies are needed to quantify how various factors can influence WBV exposures.     

Whole-body vibration-related health disorders in occupational medicine – an international comparison

Workers with whole-body vibration (WBV) exposure are likely to report non-specific health complaints. Health and safety providers may not recognise such occupational injuries and may be unfamiliar with appropriate exposure assessment and prevention. This is a review of clinical studies, medical evidence, differential diagnostic evaluation protocols, surveillance programmes, national and international standards, and interventions recommendations utilising PubMed and other online resources. In summary, several studies show a clear trend: with increasing duration and intensity of occupational WBV exposure, primarily musculoskeletal or neurological disorders of the spine occur. Other organ damage has also been reported. In some European Union countries, spinal injury caused by WBV is recognised as an occupational disease and may be compensable. The WBV-related injury diagnosis includes a review of the work history, exposure assessment and differential diagnostic evaluation. WBV health surveillance should assess health status of WBV-exposed workers and address preventive measures.     

Annual incidence of non-specific low back pain as an occupational disease attributed to whole-body vibration according to the National Dutch Register 2005–2012

Non-specific low back pain (nLBP) is the second most important reason for sick leave in the Netherlands, and more than 50% of the workers on sick leave attribute these complaints to their work. To stimulate recognition and prevention, an occupational disease (OD) registration-guideline was implemented for the assessment of the work-relatedness of nLBP in the Netherlands in 2005. The aim of this study is to present the annual incidence of nLBP as an OD and specifically for whole-body vibration (WBV) including patient characteristics such as age, sick leave and actions initiated by the occupational physician (OP). The data were retrieved from the National Dutch Register for 2005–2012. Each year about 118 OPs reported 509 cases (SD 139) of nLBP as an OD in a Dutch working population of 7.5 million workers (8% of all annual reported ODs). Less than 1% of these cases were attributed to WBV: 94% were men, 45% were between 51 and 60 years and 35% were on sick leave for more than 2 weeks. Most initiated actions were ergonomic interventions (35%).     

Evaluation of responses to broad-band whole-body vibration

Abstract

The experiment was aimed at investigating the human response to different modes, frequencies and intensities of whole-body vibration (WBV), in order to check the evaluation procedures currently recommended. Six male seated subjects were exposed to sinusoidal (SIN) and octave-band-wide vibration (OWV) in the z axis with the frequencies or centre frequencies, respectively, of 2,4, 8 and 16 Hz at two intensity levels (except for 2 Hz), in accordance with the frequency weighting of ISO 2631 (ISO 1978 a). The 14 exposure conditions were compared by means of a slightly modified, complete paired comparison, the total number of exposures amounting to 1044. Subjective judgements of the severity of WBV, annoyance and the ability to control a constant sitting posture were obtained along with the bioelectrical activity of trunk muscles, transmissibility and impedance. An integral assessment of the exposures was rendered possible by the complex evaluation of different human responses. OWV and SIN with identical a_zw r.m.s. values (ISO 1978 a) produced almost identical effects. The results clearly speak in favour of the weighting procedure. This procedure was also supported by an additional pilot study with two-octave-band-wide vibration. The superiority of the weighting procedure suggests lower limits for broad-band vibration than those recommended at present (ISO 1978 a). Human response to WBV in the range near 4 Hz was more pronounced than that of equivalent exposures with other frequencies. Generally, higher intensities induced stronger effects. The biomechanical data exhibited a non-linearity for the WBV levels of intensity investigated. The patterns of myoelectric and biomechanical reactions depended on both anatomical and exposure conditions. The individual responses in discriminating the exposure conditions significantly agreed, but the extent of agreement between the individual responses varied for the effects investigated.     

Predictive discomfort of non-neutral head-neck postures in fore-aft whole-body vibration

It seems obvious that human head-neck posture in whole-body vibration (WBV) contributes to discomfort and injury risk. While current mechanical measures such as transmissibility have shown good correlation with the subjective-reported discomfort, they showed difficulties in predicting discomfort for non-neutral postures. A new biomechanically based methodology is introduced in this work to predict discomfort due to non-neutral head-neck postures. Altogether, 10 seated subjects with four head-neck postures--neutral, head-up, head-down and head-to-side--were subjected to WBV in the fore-aft direction using discrete sinusoidal frequencies of 2, 3, 4, 5, 6, 7 and 8 Hz and their subjective responses were recorded using the Borg CR-10 scale. All vibrations were run at constant acceleration of 0.8 m/s2 and 1.15 m/s2. The results have shown that the subjective-reported discomfort increases with head-down and decreases with head-up and head-to-side postures. The proposed predictive discomfort has closely followed the reported discomfort measures for all postures and rides under investigation. STATEMENT OF RELEVANCE: Many occupational studies have shown strong relevance between non-neutral postures, discomfort and injury risk in WBV. With advances in computer human modelling, the proposed predictive discomfort may provide efficient ways for developing reliable biodynamic models. It may also be used to assess discomfort and modify designs inside moving vehicles.     

Evaluating worker vibration exposures using self-reported and direct observation estimates of exposure duration

The objective of this study was to compare objective and subjective methods of collecting exposure time data for hand arm vibration (HAV) and whole-body vibration (WBV), and to evaluate the impact of inaccurate exposure times’ on the calculation of the average vibration exposure over an 8 h working day A(8).The study was carried out in the engineering services and maintenance departments of a construction and property management company. Worker exposure time data was collected using three methods, questionnaire surveys, daily worker interviews and 8 h direct workplace observations. Vibration magnitudes (m/s²) were measured for a range of hand tools and vehicles, and daily vibration exposure estimates A(8) were calculated using exposure times observed, reported in interview and self reported in the questionnaire.Results from the study showed that self-reported exposure time estimates from the questionnaire survey were a factor of 9.0 (median value) times greater for HAV and a factor of 6.0 (median value) times greater for WBV when compared with direct observation estimates. Exposure times reported in interview were higher, than those observed, but more reliable than those self reported in the questionnaire; a factor of 2.1 (median value) times greater for HAV and a factor of 1.4 (median value) times greater for WBV. A(8) values calculated using questionnaire exposure times were up to 66% and 75% greater for sources of HAV and WBV respectively when compared to A(8) values calculated using observed exposure times.For the purposes of carrying out a reliable risk assessment, results from this study indicate that direct measurements of worker exposure time are not recommended over questionnaires especially where work is highly variable for example in construction and property management. Worker interviews or direct workplace observation methods were found to be reliable alternative methods for collecting exposure time.     

Six-degree-of-freedom whole-body vibration exposure levels during routine skidder operations

This research focuses on quantifying six-degree-of-freedom (6-DOF) whole-body vibration (WBV) exposure levels that occur in Northern Ontario skidders during routine field operating tasks. 6-DOF vibration running root-mean-square (RMS) acceleration levels at the operator/seat interface were determined for eight skidders while driving loaded, driving unloaded, picking up a load, dropping off a load and ploughing logs under field operating conditions. The acceleration data were weighted in accordance with ISO 2631–1:1997 and evaluated for both health and comfort outcomes. The mean running RMS weighted translational and rotational accelerations all exceeded 0.36 m/s² and 0.14 rad/s². The greatest average accelerations occurred while driving unloaded with this condition displaying translational vibration total values (VTV) that exceeded the upper limit of the ISO 2631–1:1997 health caution zone within an average of 2.3 h. Utilizing 6-DOF VTV, virtually all operating conditions would be designated as uncomfortable.

Statement of Relevance: This study provides one of the most comprehensive reports on vibration exposures in seated vehicle operators. The results are geared towards ergonomists with discussions on health effects and measurement concerns, while providing the raw vibration exposure data that will be useful to vehicle, component and vibration sensor designers.     

Evaluating worker vibration exposures using self-reported and direct observation estimates of exposure duration

The objective of this study was to compare objective and subjective methods of collecting exposure time data for hand arm vibration (HAV) and whole-body vibration (WBV), and to evaluate the impact of inaccurate exposure times’ on the calculation of the average vibration exposure over an 8 h working day A(8).The study was carried out in the engineering services and maintenance departments of a construction and property management company. Worker exposure time data was collected using three methods, questionnaire surveys, daily worker interviews and 8 h direct workplace observations. Vibration magnitudes (m/s²) were measured for a range of hand tools and vehicles, and daily vibration exposure estimates A(8) were calculated using exposure times observed, reported in interview and self reported in the questionnaire.Results from the study showed that self-reported exposure time estimates from the questionnaire survey were a factor of 9.0 (median value) times greater for HAV and a factor of 6.0 (median value) times greater for WBV when compared with direct observation estimates. Exposure times reported in interview were higher, than those observed, but more reliable than those self reported in the questionnaire; a factor of 2.1 (median value) times greater for HAV and a factor of 1.4 (median value) times greater for WBV. A(8) values calculated using questionnaire exposure times were up to 66% and 75% greater for sources of HAV and WBV respectively when compared to A(8) values calculated using observed exposure times.For the purposes of carrying out a reliable risk assessment, results from this study indicate that direct measurements of worker exposure time are not recommended over questionnaires especially where work is highly variable for example in construction and property management. Worker interviews or direct workplace observation methods were found to be reliable alternative methods for collecting exposure time.     

Factors affecting the perception of whole-body vibration of occupational drivers: an analysis of posture and manual materials handling and musculoskeletal disorders

Due to the high cost of conducting field measurements, questionnaires are usually preferred for the assessment of physical workloads and musculoskeletal disorders (MSDs). This study compares the physical workloads of whole-body vibration (WBV) and awkward postures by direct field measurements and self-reported data of 45 occupational drivers. Manual materials handling (MMH) and MSDs were also investigated to analyse their effect on drivers' perception. Although the measured values for WBV exposure were very similarly distributed among the drivers, the subjects' perception differed significantly. Concerning posture, subjects seemed to estimate much better when the difference in exposure was significantly large. The percentage of measured awkward trunk and head inclination were significantly higher for WBV-overestimating subjects than non-overestimators; 77 and 80% vs. 36 and 33%. Health complaints in terms of thoracic spine, cervical spine and shoulder–arm were also significantly more reported by WBV-overestimating subjects (42, 67, 50% vs. 0, 25, 13%, respectively). Although more MMH was reported by WBV-overestimating subjects, there was no statistical significance in this study.