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

Study on the biodynamic characteristics and internal vibration behaviors of a seated human body under biomechanical characteristics

To provide reference and theoretical guidance for establishing human body dynamics models and studying biomechanical vibration behavior, this study aimed to develop and verify a computational model of a three-dimensional seated human body with detailed anatomical structure under complex biomechanical characteristics to investigate dynamic characteristics and internal vibration behaviors of the human body. Fifty modes of a seated human body were extracted by modal method. The intervertebral disc and head motions under uniaxial white noise excitation (between 0 and 20 Hz at 1.0, 0.5 and 0.5 m/s2 r.m.s. for vertical, fore-aft and lateral direction, respectively) were computed by random response analysis method. It was found that there were many modes of the seated human body in the low-frequency range, and the modes that had a great impact on seated human vibration were mainly distributed below 13 Hz. The responses of different positions of the spine varied greatly under the fore-aft and lateral excitation, but the maximum stress was distributed in the lumbar under different excitations, which could explain why drivers were prone to lower back pain after prolonged driving. Moreover, there was a large vibration coupling between the vertical and fore-aft direction of an upright seated human body, while the vibration couplings between the lateral and other directions were very small. Overall, the study could provide new insights into not only the overall dynamic characteristics of the human body, but also the internal local motion and biomechanical characteristics under different excitations.

Investigating the effect of hot and cold polyurethane foam on reducing whole body vibration of forklift operators

BACKGROUND

Vibration is one of the harmful factors for forklift drivers. The use of non- standard seats and not paying attention to how the seats are maintained can be affected by the amount of vibration transmitted to the person.

OBJECTIVE

This study investigates the amount of vibration transmitted from the forklift and the effect of different types of polyurethane foam in reducing the vibration transmitted from the forklift seat.

METHODS

This descriptive-analytical study was performed on 38 forklifts in 4 diesel models with the same weight class. The amount of vibration transmitted from forklift seats according to ISO2631 standard, taking into account the effect of various factors such as foam type (hot and cold), thickness (6-12 cm), load and year Function was measured. The amount of vibration caused by the forklift on the seat and under the seat was evaluated using ISO7096 standard.

RESULTS

The average total vibration of the whole body in all foams in no-load mode is more than with load. The transmission vibration of cold polyurethane foam is less than that of hot polyurethane foam. With increasing thickness, the efficiency of cold polyurethane foam increases by 12 cm and in the loaded state 40.63% and in the unloaded state 49.58% in reducing the vibration transmitted to drivers.

CONCLUSION

The results of this study show that cold foam has better effectiveness and efficiency than hot polyurethane foam. Also, the thicker the foam, the less vibration is transmitted to the driver.

Applications of wireless sensor networks to improve occupational safety and health in underground mines

INTRODUCTION

The very complex and hazardous environment of underground mines may significantly contribute to occupational fatalities and injuries. Deploying wireless sensor network (WSN) technology has the potential to improve safety and health monitoring of miners and operators. However, the application of WSN in the industry is not fully understood and current research themes in this area are fragmented. Thus, there is a need for a comprehensive review that directly explores the contribution of WSNs to occupational safety and health (OSH) in underground mines.

METHOD

This study aims to conduct a systematic literature review on the existing applications of WSNs for improving OSH in the underground mining industry to pinpoint innovative research themes and their main achievements, reveal gaps and shortcomings in the literature, recommend avenues for future scholarly works, and propose potential safety interventions. The major contribution of this review is to provide researchers and practitioners with a holistic understanding of the integration of WSN applications into underground mine safety and health management.

RESULTS

The review results have been categorized and discussed under three predominant categories including location monitoring and tracking, physiological and body kinematics monitoring, and environmental monitoring. Finally, seven major directions for future research and practical interventions have been identified based on the existing research gaps including: (1) further applications of WSNs for underground mining OSH management; (2) application of WSNs from research to real-world practice; (3) big data analytics and management; (4) deploying multiple WSNs-based monitoring systems; (5) integration of WSNs with other communication systems; (6) adapting WSNs to the Internet of Things (IoT) infrastructure; and (7) autonomous WSNs.

Automotive Seat Comfort and Vibration Performance Evaluation in Dynamic Settings

An automotive seat is a key component which not only provides restraint and support for its occupant, but also mitigates vibration. Since an automotive seat is in constant contact with the vehicle occupant, its dynamic comfort is of great importance in automotive seat designs. In this study, three automotive seats with different foam firmnesses were evaluated to understand how the foam firmness, through different foam formulations, affected the seat vibration performance and perceived dynamic comfort in a laboratory (study 1) and field setting (study 2). In a repeated-measures laboratory based study, whole-body vibration (per ISO 2631-1), self-reported body discomfort, and seating comfort were measured and compared among the three automotive seats while participants were exposed to tri-axial, field-measured, automotive vibration and X-Y-Z axis 1–30 Hz sine sweeps. In a subsequent ride-and-drive field study, the two seats that received the highest comfort ratings from the laboratory study were installed in two identical vehicles and whole body vibration (WBV) and self-reported seating comfort were evaluated by the participants. The results showed that the foam firmness significantly affected WBV measures and self-reported comfort (p < 0.05). This study demonstrated that altering foam formulation can be an effective way of further improving dynamic vibration and seat comfort performance.

Relationships between Height, Mass, Body Mass Index, and Trunk Muscle Activation during Seated Whole-Body Vibration Exposure

Operators of heavy equipment are often exposed to high levels of whole-body vibration (WBV), which has been associated with a variety of adverse health outcomes. Although anthropometric factors are known to impact vibration dose and risk of low back pain, studies have yet to investigate the influence of anthropometric factors on muscle activation during WBV exposure. This study quantified the relationships between muscle activation, vibration frequency, body mass, body mass index (BMI), and height both pre- and post-fatigue. Muscle activation of the external oblique (EO), internal oblique (IO), lumbar erector spinae (LE) and thoracic erector spinae (TE) were quantified using surface electromyography. Results indicate increased activation with increased mass, BMI, and frequency for the LE, TE, and IO, which may be a result of increased activation to stabilize the spine. Decreased muscle activation with increased height was seen in the TE, IO, and pre-fatigue EO, which could indicate higher risk for low back injury since height is associated with increased forces on the spine. This may contribute to the association between increased low back pain incidence and increased height. Results suggest that ISO 2631-1 health guidance should incorporate anthropometric factors, as these may influence muscle activation and back injury risk.

A Comprehensive Review of Work-Related Musculoskeletal Disorders in the Mining Sector and Scope for Ergonomics Design Interventions

OCCUPATIONAL APPLICATIONS Work-related Musculoskeletal Disorders (WMSDs) are prevalent in many industries worldwide, including the large and labor-intensive mining sector. A systematic review was carried out to understand problems in the mining sector issues from three broad perspectives: 1) the prevalence of WMSDs among miners; 2) the association of occupational, psychosocial, environmental, and other risk factors with WMSDs causation; and 3) ergonomics interventions already proposed or implemented, and scope for design interventions. Our review revealed that automation, job aids, and displays are methods suitable for ergonomic design interventions. Ergonomic intervention strategies at various hierarchical levels, and the successive way forward as proposed in our review, could act as a catalyst in formulating problem-specific solution strategies by the participation of diverse stakeholders to implement a more human-centric workplace.

Whole-Body Vibration and Trunk Posture During Operation of Agricultural Machinery

Exposure to whole-body vibration (WBV) is common among agricultural workers and is associated with musculoskeletal health outcomes such as low back pain. Little is known, however, about the characteristics of exposure experienced during actual production practices. We measured WBV levels during agricultural machinery use among a sample of farmers (n = 55) performing routine agricultural activities and explored machinery attributes that may explain WBV summary measures. We also measured trunk posture to provide additional information about physical exposures during machinery operation. Measurements were made on-farm and during actual work conditions of a sample of agricultural machines (n = 112), including tractors, combines, heavy utility vehicles, and all-terrain vehicles (ATVs). Results indicated the presence of high levels of vibration (median frequency-weighted root-mean-square acceleration of approximately 0.8 m s-2) with time signatures that include high-amplitude mechanical shocks (median crest factor of nearly 23). Compared to other machinery types, combines exhibited the lowest WBV levels and among the most favorable trunk postures. Substantial variability was observed in both the WBV and trunk posture summary measures, suggesting for future studies that alternative sampling strategies are needed to fully capture temporal patterns of machinery use.

Identifying Equipment Factors Associated with Snowplow Operator Fatigue

A recent body of research in fatigue management indicates that other factors, including in-cab and external equipment, contribute to operator fatigue. The goal of this project was to identify winter road maintenance equipment (in-cab and external) that may increase or mitigate snowplow operator fatigue. To accomplish this goal, questionnaires from 2011 snowplow operators were collected from 23 states in the U.S. Results confirmed previous research that fatigue is prevalent in winter road maintenance operations. Winter road maintenance equipment that produced excessive vibrations, noise, reduced visibility, and complex task demands were found to increase snowplow operators’ self-reported fatigue. Similarly, equipment that reduced vibrations and external noise, improved visibility, and limited secondary tasks were found to reduce snowplow operator’s self-reported fatigue. Based on the questionnaire responses and the feasibility of implementation, the following equipment may help to mitigate or prevent snowplow operator fatigue: dimmable interior lighting, LED bulbs for exterior lighting, dimmable warning lights, a CD player or satellite radio in each vehicle, heated windshield, snow deflectors, narrow-beam auxiliary lighting, and more ergonomically designed seats with vibration dampening/air-ride technology.

Review on Seat Suspension System Technology Development

This review will focus on the necessity for developing seat vibration control systems as a part of manufacturers’ investigation into finding innovative methods to increase the comfort and safety of the vehicles’ drivers. Operators of either on-road or off-road vehicles are regularly subjected to an extended variety of various vibration levels, especially at low frequencies. Considering that exposure to such vibration in long term has some damaging effects on driver’s health, many comprehensive investigations have been carried out and researchers have proposed several measures for estimating discomfort and the suitability of various vehicles’ seats such as those of trucks, cars and agricultural vehicles in operating condition. Active, passive and semi-active suspension systems are employed in vehicle seats to alleviate the harmful and damaging effects due to the transmitted vibration to the human body. In order to improve riding comfort, the operator’s body displacement and acceleration must be reduced. According to the research, active suspension control systems are the best choice to reduce the transmitted vibration to the drivers’ body and provide the best ride comfort in comparison with passive and semi-active systems.

Whole-body vibration and back pain-related work absence among heavy equipment vehicle mining operators

Objective

To determine the association between several whole-body vibration (WBV) exposure estimates and back pain-related work absence.

Methods

Exposures (based on the weighted daily root mean square acceleration, A(8); the daily vibration dose value, VDV(8); and the daily equivalent static compression dose, Sed(8)) of 2302 workers during 4 years were estimated using each worker’s monthly vehicle operation records and WBV measurements from 11 different types of heavy equipment vehicles in a large coal mine. Company payroll data provided work absence during the concurrent 4 years of exposure. Cox regression models estimated the associations between the different WBV metrics and time to first work absence related to back pain. An adjusted R2 statistic provided a measure of model fit.

Results

All estimated metrics of WBV exposures were positively and significantly associated with back pain-related absence. HRs varied from 2.03 to 12.39 for every 0.21 m/s2 increase in the A(8)-based exposures; from 1.03 to 1.18 for every 1.72 m/s1.75 increase in VDV(8)-based exposures; and from 1.04 to 1.07 for every 0.06 MPa increase in Sed(8)-based exposures. Models using the estimated VDV(8) metric for the z axis fit the data best as measured by the R2 statistic.

Conclusion

Higher WBV exposures were associated with back pain-related absences in this population, which appears after a few years of follow-up. Introducing controls to lower exposure levels may help reduce back pain-related work absences.

Prioritization of practical solutions for the vibrational health risk reduction of mining trucks using fuzzy decision making

The goal of this article was to prioritize the practical solutions for vibrational health risk reduction of truck drivers during mining operation using the multicriteria decision-making (MCDM) techniques. Mining trucks require special consideration because of their specific suspension system, large size, payload capacity, and off-road conditions of mining. In most cases, it is not easy for decision makers to compute verbal and linguistic variables, whose values are expressed in linguistic terms. These uncertainties and ambiguities are well interpreted by using fuzzy set theory. In this study, the MCDM methods were used under fuzzy environment. As a result, seat suspension maintenance was offered as the best solution to attenuate the vibrations and decrease the injuries related to the WBV exposure. The driver training, haul road construction and maintenance, lighting and visibility improvement and work organization were found as the other solutions, respectively.

A Randomized Controlled Trial of a Truck Seat Intervention: Part 1-Assessment of Whole Body Vibration Exposures

Full-time vehicle and heavy equipment operators often have a high prevalence of musculoskeletal disorders, especially low back pain (LBP). In occupations requiring vehicles or heavy equipment operation, exposure to whole body vibration (WBV) has been consistently associated with LBP. LBP is the most common cause of work-related disability and continues to be the leading cause of morbidity and lost productivity in the US workforce. Using a parallel randomized controlled trial design, over a 12-month period, this study evaluated two different seating interventions designed to reduce WBV exposures. Forty professional truck drivers were initially recruited and randomly assigned to one of two groups: (i) a passive suspension/control group-20 drivers who received a new, industry-standard air-suspension seat, and (ii) an intervention group-20 drivers who received an active-suspension seat, which has been shown to reduce vertical WBV exposures by up to 50% compared to passive seats. WBV exposures from the truck seat and floor were collected during driver's full shifts (6-18 h) before (pre-intervention) and after the intervention (0, 3, 6, and 12 months post-intervention) per International Standards Organization (ISO) 2631-1 and 2631-5 WBV standards. After subject dropout and turnover, 16 truck drivers remained in each group. The pre-intervention WBV data showed that there were no differences in the daily equivalent time-weighted average WBV exposures [A(8)], vibration dose values [VDV(8)], and static spinal compression doses [Sed(8)] between the two groups (P's > 0.36). After the new seats were installed, the A(8) values showed that the active suspension/intervention group experienced much greater reduction in the vertical (z) axis [~50%; P = <0.0001; Cohen's d effect size (95% CI) = 1.80 (1.12, 2.48)] exposures when compared to in the passive suspension/control group [~20%; P = 0.23; 0.33 (-0.36, 1.02)]. The post-intervention z-axis VDV(8) and Sed(8) WBV exposure measures were not different between the two seat groups [VDV(8), P = 0.33; 0.35 (-0.32, 1.03); Sed(8), P = 0.61; 0.08 (-0.59, 0.76)]. These study findings indicate that, relative to the current industry-standard, passive air-suspension seats which are ubiquitous in all semi-trucks today, the active suspension seat dramatically reduced average continuous [A(8)] WBV exposures but not periodic, cumulative impulsive exposures [VDV(8) and Sed(8)].

Evaluation of commercially available seat suspensions to reduce whole body vibration exposures in mining heavy equipment vehicle operators

As mining vehicle operators are exposed to high level of Whole body vibration (WBV) for prolonged periods of time, approaches to reduce this exposure are needed for the specific types of exposures in mining. Although various engineering controls (i.e. seat suspension systems) have been developed to address WBV, there has been lack of research to systematically evaluate these systems in reducing WBV exposures in mining heavy equipment vehicle settings. Therefore, this laboratory-based study evaluated the efficacy of different combinations of fore-aft (x-axis), lateral (y-axis), and vertical (z-axis) suspensions in reducing WBV exposures. The results showed that the active vertical suspension more effectively reduced the vertical vibration (∼50%; p's < 0.0001) as compared to the passive vertical suspension (10%; p's < 0.11). The passive fore-aft (x-axis) and lateral (y-axis) suspension systems did not attenuate the corresponding axis vibration (p's > 0.06) and sometimes amplified the floor vibration, especially when the non-vertical vibration was predominant (p's < 0.02). These results indicate that there is a critical need to develop more effective engineering controls including better seat suspensions to address non-vertical WBV exposures, especially because these non-vertical WBV exposures can increase risks for adverse health effects including musculoskeletal loading, discomfort, and impaired visual acuity.

The effect of a multi-axis suspension on whole body vibration exposures and physical stress in the neck and low back in agricultural tractor applications

Whole body vibration (WBV) exposures are often predominant in the fore-aft (x) or lateral (y) axis among off-road agricultural vehicles. However, as the current industry standard seats are designed to reduce mainly vertical (z) axis WBV exposures, they may be less effective in reducing drivers' exposure to multi-axial WBV. Therefore, this laboratory-based study aimed to determine the differences between a single-axial (vertical) and multi-axial (vertical + lateral) suspension seat in reducing WBV exposures, head acceleration, self-reported discomfort, and muscle activity (electromyography) of the major muscle of the low back, neck and shoulders. The results showed that the multi-axial suspension seat had significantly lower WBV exposures compared to the single-axial suspension seats (p' < 0.04). Similarly, the multi-axial suspension seat had lower head acceleration and muscle activity of the neck, shoulder, and low back compared to the single-axial suspension seat; some but not all of the differences were statistically significant. These results indicate that the multi-axial suspension seat may reduce the lateral WBV exposures and associated muscular loading in the neck and low back in agricultural vehicle operators.

Whole-body Vibration Exposure Intervention among Professional Bus and Truck Drivers: A Laboratory Evaluation of Seat-suspension Designs

Long-term exposure to seated whole-body vibration (WBV) is one of the leading risk factors for the development of low back disorders. Professional bus and truck drivers are regularly exposed to continuous WBV, since they spend the majority of their working hours driving heavy vehicles. This study measured WBV exposures among professional bus and truck drivers and evaluated the effects of seat-suspension designs using simulated field-collected data on a vibration table. WBV exposures were measured and compared across three different seat designs: an air-ride bus seat, an air-ride truck seat, and an electromagnetically active (EM-active) seat. Air-ride seats use a compressed-air bladder to attenuate vibrations, and they have been in operation throughout the transportation industry for many years. The EM-active seat is a relatively new design that incorporates a microprocessor-controlled actuator to dampen vibration. The vibration table simulated seven WBV exposure scenarios: four segments of vertical vibration and three scenarios that used field-collected driving data on different road surfaces-a city street, a freeway, and a section of rough roadway. The field scenarios used tri-axial WBV data that had been collected at the seat pan and at the driver's sternum, in accordance with ISO 2631-1 and 2631-5. This study found that WBV was significantly greater in the vertical direction (z-axis) than in the lateral directions (x-and y-axes) for each of the three road types and each of the three types of seats. Quantitative comparisons of the results showed that the floor-to-seat-pan transmissibility was significantly lower for the EM-active seat than for either the air-ride bus seat or the air-ride truck seat, across all three road types. This study also demonstrated that seat-suspension designs have a significant effect on the vibrations transmitted to vehicle operators, and the study's results may prove useful in designing future seat suspensions.

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.

PRACTITIONER SUMMARY

Low back pain is common in bus drivers and studies have shown a relationship with whole body vibration. Relative to a pedestal seat with its limited travel seat suspension, the air-suspension seat with its longer travel suspension provided little additional benefit. Exposures were below European Union daily exposure action values.

Vibration analysis of the sulky accessory for a commercial walk-behind lawn mower to determine operator comfort and health

A sulky is a single-wheeled platform attachment on which the operator of a commercial walk-behind lawn mower rides while standing. The effects of sulky vibration on operator comfort and health have not been investigated. In this study, tri-axial accelerometers measured sulky vibration during mower use by two commercial mowers on varied terrain and 12 volunteer mowers over a controlled course. The accelerometer data were processed according to methods established in ISO 2631. Results indicate the mean frequency-weighted root mean square (RMS) acceleration sums fall into the 'very uncomfortable' range for vibration of standing persons (1.9 ± 0.48 m s⁻²). Additionally, vibration dose values indicated that the mean vibration dosages exceeded the daily exposure limit values established in Directive 2002 /44/EC (z-axis A(8) value of 1.30 ± 34 m s⁻²; VDV(exp) value of 28.1 ± 6.25 m s⁻¹·⁷⁵). This information suggests that modifications including vibration damping should be added to the sulky to reduce rider discomfort and health risks.

PRACTITIONER SUMMARY

This study investigated the effects of vibration during use of a commercial lawn mowing sulky. Findings from accelerometer data suggest that the vibration experienced by sulky operators is significant enough to cause discomfort and health risks which may lead to personnel turnover or long-term effects for the operator.

Vehicle design influences whole body vibration exposures: effect of the location of the front axle relative to the cab

Using a repeated measure design, this study compared differences in whole body vibration (WBV) exposures among 13 drivers who drove a truck with the cab over the front axle (cab-over design) and a truck with the cab situated behind the front axle (non-cab-over design). The drivers drove both trucks over a standardized route that comprised three distinct segments: a freeway segment, a city street segment with stop-and-go driving (traffic lights), and a city street segment without traffic lights. A portable WBV data acquisition system collected tri-axial time-weighted and raw WBV data per ISO 2631-1 and 2631-5 standards. Simultaneous global positioning system (GPS) data were also collected to compare vehicle speeds. The GPS data indicated that there were no speed differences between the two vehicles. However, average and impulsive z-axis vibration levels were significantly higher for the cab-over design than for the non-cab-over design. In addition, significant WBV exposure differences between road types were found, with the freeway segments having the lowest exposures and the city street segments without traffic lights having the highest exposures. Vehicle type and the associated WBV exposures should be considered when purchasing vehicles to be used by full-time professional vehicle operators.