WHOLE-BODY VIBRATION EXPOSURE AND MUSCULOSKELETAL DISORDERS OF HEAVY EQUIPMENT OPERATORS IN CONSTRUCTION

Exposure to vibration is common in industrial occupations. In fact, the construction industry has one of the highest exposures to single-point and whole-body vibrations (WBV). One of the most common conditions associated with WBV exposure is musculoskeletal disorders (MSD). This research aims to measure the WBV levels of heavy equipment in construction and quantify the MSD prevalence of the operators. It used two methods to assess the MSD levels of the operators and record the WBV levels of the construction vehicles. A standardized questionnaire on MSDs developed by Corlett and Bishop (1976) is utilized. To measure the WBV levels, a PCB Piezotronics seat-pad triaxial accelerometer (model #356M193) connected to a Larson Davis Human Vibration Meter 200 is used. Expressed in root mean square acceleration and vibration dose value, the WBV values recorded are compared to the reference provided by the 1997 ISO 2631-1 whole-body vibration standards. In total, there are 19 various pieces of heavy equipment and 19 operators surveyed. The results show no overexposure in any of the vehicles tested. Also, the level of MSD prevalence is high in the lower back, mid-back, neck, shoulder, and buttocks. Further research is required, including a larger sample size of heavy equipment and operators, different terrains and locations, and a study design that confirms a statistical relationship between WBV and MSD in this industry.

KEY WORDS: whole-body vibration, musculoskeletal disorders, low back pain, construction, safety

Each day, people are subject to different amounts of vibrations from activities such as traveling by bus or train. Even some occupations, like heavy machine operators or truck drivers, expose their workers to long hours of whole-body vibrations (WBV). WBV is caused by vibration transmitted through the seat or the feet by workplace machines and vehicles. These vibrations, in turn, are transmitted throughout the user’s nervous and musculoskeletal system. WBV frequencies range from 2 to 100 Hz (Levy, 2006). However, risks are greatest when vibration magnitudes are high, and exposure duration is long, frequent, and regular and includes several shocks or jolts.

Exposure to WBV is common in industrial occupations. In fact, the construction industry has one of the highest exposures to single-point vibration and WBV (Vergara et al., 2008; Cann et al., 2003). Long exposure to WBV in a vertical direction may cause an increase in respiratory and heart rates, disturbance in position sense, balance, visual performance, mental processing, fatigue, low back pain, and a variety of gastrointestinal and MSD (Monazzam et al., 2018; Zare, Nazifipour, and Yari, 2020; Yung et al., 2017). It has been reported that nearly 72 million males and 1.8 million females in the United Kingdom are exposed to WBV. Similarly, around 40 million workers suffer from WBV-induced MSD in the European Union (Palmer, 2000). In the United States, nearly 2 million workers suffer from work-related MSD, which costs between 45 to 54 billion dollars annually (Carayon, Smith, and Haims, 1999). The construction industry has an MSD incident rate of almost 30% (US BLS, n.d.). Therefore, of the 2 million workers with injury or illness from an MSD, 600,000 of them work in the construction industry.

In the US, standards are available for reference, but there are no specific regulations such as those coming from the Occupational Safety and Health Administration (OSHA) that mandate WBV identification, monitoring, and control. Some of the commonly used standards include the International Standardization Organization (ISO) 2631-1:1997 on mechanical vibration and shock evaluation of human exposure to WBV (ISO, 1997), the European Agency for Safety and Health at Work Directive 2002/44/EC on vibration that aims at ensuring health and safety of each worker and creating a minimum basis of protection for all community workers from vibration risks  (Griffin et al., 2012), and the threshold limit values (TLV) provided by the American Conference of Governmental Industrial Hygienists (ACGIH) (Dinuoscio, 2022).

The most heavy equipment vehicles in construction are used to transfer, smooth, or level earth and dig holes. According to the findings of Cann et al. (2003), scrapers, skid steer vehicles, dump trucks, wheel loaders, bulldozers, and excavators are some of the heavy construction equipment that can emit WBV doses ranging from 0.92 to 1.61 m/s². When comparing the WBV for vehicles, the ISO has the 1997 ISO 2631-1 standards on comfort caution zone and perception ranges. In this standard, a root mean square (RMS) acceleration range of 0.80 m/s² to 1.60 m/s² is considered uncomfortable, while a value of more than 2 m/s² is extremely uncomfortable (ISO, 1997). However, research that investigates the levels of WBV and their potential effects on MSD prevalence in the construction industry in the US is scarce. We hypothesize that in the last decade there have been significant improvements on the design of heavy equipment in construction. However, we cannot be certain if WBV levels are now minimal in these newer models of heavy equipment. Thus, more studies narrowed to certain occupations are necessary to provide better understanding of the hazard and improve prevention strategies. This paper looks to address some gaps surrounding WBV and MSD in the US. Specifically, it aims to measure the WBV levels of heavy equipment and quantify the MSD prevalence of the operators.

 2.1 Study Design, Participants, and Instrumentation

This descriptive study received IRB approval with protocol number 456. The study participants included 19 construction workers who operated heavy equipment. Convenience sampling was used due to the researchers’ limited access to construction projects around the New England area. The participants were contacted through multiple contractors or their respective supervisors. They were chosen for this study based on their location, their occupation, the type of equipment they use at work, and their consent to participate.

This study uses two parameters to assess the MSD levels of the operators and record the WBV levels of the heavy equipment. A standardized questionnaire on MSD developed by Corlett and Bishop (1976) was utilized. The first part of the questionnaire asked about the operators’ personal and work-related profiles. Also, it had participants fill out their biometrics, such as daily time spent operating heavy machinery, years as an operator, and training. The MSD questionnaire was divided into different body portions, such as the neck, shoulders, upper arms, lower arms, back, lower back, buttocks, upper legs, and lower legs. Each was charted on a scale of 0 to 5—with 0 being no pain and 5 being almost unbearable.

To measure the WBV levels, a PCB Piezotronics seat-pad triaxial accelerometer (model #356M193) was placed on each operator’s seat in accordance with the ISO 2631-1 guidelines (ISO, 1997). The accelerometer was sensitive to vibration frequencies between 0.5 and 5000 Hz. Each measurement took place on three orthogonal axes (x-, y-, and z-directions), where the x-axis was positioned for vibration traveling in the sagittal plane, the y-axis in the coronal plane, and z-axis in the vertical plane. The accelerometer was connected to a Larson Davis Human Vibration Meter (HVM) 200 vibration monitor, which recorded the incoming vibration signal. Both the accelerometer and HVM 200 were calibrated by the manufacturers upon purchase.

Each operator was asked to sit on the accelerometer for a continuous 20-minute sample for each equipment. This duration was deemed appropriate to ensure that all aspects of the work cycle were represented and as previously described (Cann et al., 2003). Also, this chosen sampling period met the ISO 2631-1 guidelines and is relatively long compared to other time-and-event, principle-guided data gathering in other research (Schneider, Kittusamy, and Buchholz, 2001; Malchaire and Piette, 1991).

It was previously proposed that both the RMS accelerations and the vibration dose value (VDV) are good measures due to the possibility of testing on surfaces that result in more jolting or repeated shock to the operator (Cann et al., 2003). The VDV is a better measure for jolting or repeated shock vibrations because it uses a time-dependent fourth root of the integral of the weighted acceleration instead of the square root used in the RMS acceleration calculations (ISO, 1997). The use of the ISO 2631-1 standards was preferred instead of the ACGIH’s TLV because the measurement equipment only provided weighted RMS accelerations and VDV, which are better suited for comparison with the ISO 2631-1 standard (ISO, 1997). Also, compared to the three available versions of ISO’s WBV standard (1997, 2014, and 2018), the researchers preferred the 1997 version because it has been tested to be reliable and valid by previous studies (Erdem et al., 2020; Duarte et al., 2020; Akinnuli et al., 2018; Marin et al., 2017; Cann et al., 2003).

To compare the collected VDV data, the researchers used a value from the ISO 2631-1 standards. A VDV value that exceeds 8.5 m/s^1.75 places the operator at a greater probability of adverse health effects (ISO, 1997). When comparing the RMS acceleration values of the heavy equipment tested, the researchers referenced the same standard with values ranging from <0.315 m/s² (not uncomfortable) to >2 m/s² (extremely uncomfortable) (Table 1).

2.2 Data Gathering and Analysis

Various construction sites throughout the New England area were visited on multiple occasions from July 2021 to April 2022. Workers were gathered upon arrival at a site and given a summary of the study, such as its objectives, data-gathering methods, and expectations. It was emphasized that their participation was voluntary. Afterward, they were given a questionnaire on MSD to fill out. Next, the heavy equipment operators were handed the seat-pad triaxial accelerometer to sit on. The Larson Davis HVM 200 that was connected to the accelerometer was also given to the operator and placed either in the pocket of their clothing or in a safe section of the seat. The HVM 200 was switched on and off through the LD Atlas application on a cellular device. The information displayed on the screen included real-time vibration levels and duration of data collection. Each operator spent 20 minutes sitting on the device. The same procedures were utilized for each operator. Nine types of heavy equipment were surveyed in this study, with a total of 19 pieces, namely: bulldozer (3), compact roller (1), dump truck (1), forklift (2), front loader (4), impact hammer excavator (1), large excavator (5), mower (1), and a small excavator (1). Most of this heavy equipment was used for smoothing, leveling, and transporting earth or materials and digging holes in the ground.

The personal and work-related data of the study participants were presented in mean and standard deviations. Percentages were used to show the prevalence of MSD according to specific body regions. The vibration values were recorded using the average of the weighted RMS acceleration, VDV, peak, and individual axis (x, y, and z) values. Both the RMS and peak values are presented in m/s^2, and the VDV is in m/s^1.75. All analyses were run through Microsoft Excel 2019.

Table 2 shows the personal and occupational characteristics of the study participants. The average age is 47 years and all operators surveyed are male. The mean weight of the participants is 91 kg, while their mean height is 1.8 meters. On average, the heavy equipment operators are overweight (28.7 kg/m²). Also, the study participants get an average of 7 hours of sleep per night. As to their occupational characteristics, the construction equipment they operate has an average age of 6 years, and they use them for at least 8 hours a day. The participants have been operating heavy equipment for 18 years on average, and 63% reported having received training on how to properly maneuver the heavy equipment.

Five large excavators, four front loaders, and three bulldozers were measured for WBV frequencies in this study (Table 3). The highest RMS values were found in large excavators (0.07 m/s²), followed by the compact roller (0.04 m/s²). The lowest average RMS was found in the end dump truck (0.02 m/s²), impact hammer excavator (0.02 m/s²), and small excavator (0.02 m/s²). As to the average VDV, large excavators were found to be the highest (1.77 m/s^1.75), followed by the forklift (0.52 m/s^1.75), and compact roller (0.40 m/s^1.75). The small excavator (0.25 m/s^1.75) and mower (0.28 m/s^1.75) had the lowest VDV values. The average peak value was seen in large excavators (2.78 m/s²) and in the forklift (0.55 m/s²), and the small excavator had the lowest peak value (0.27 m/s²).

The RMS and VDV, according to three orthogonal axes (x, y, and z), are presented in Table 4. It can be seen that the forklift has the highest VDV, ranging from 0.15 m/s^1.75 to 0.52 m/s^1.75 for all three axes. The lowest VDV values for the x-axis are seen on the impact hammer excavator and large excavator (0.24 m/s^1.75), bulldozer for the y-axis (0.16 m/s^1.75), and mower (0.73 m/s^1.75) and small excavator (0.82 m/s^1.75) for the z-axis. In terms of RMS, the highest x-axis value is recorded from the forklift (0.30 m/s²), while the compact roller has the highest dose of 0.05 m/s² for the y- and z-axes. The small excavator has the lowest RMS values for all three axes.

The workers reported a prevalence of MSD in the lower, mid, and upper back, neck, shoulders, buttocks, upper arms, lower arms, left and right thighs, and the left and right legs (Fig. 1). As to the body part with the highest prevalence, the operators had the most pain in the lower back (53%), mid-back (42%), and the neck, shoulders, and buttocks (37%). The legs (16%) and the left (21%) and right (26%) thighs had the lowest complaint of pain.

Figure 1. Prevalence of musculoskeletal disorders according to body region (n=19)

The main goal of this study was to measure the WBV levels emitted by different heavy equipment and survey the subjective MSD symptoms of the operators. Overall, the levels of WBV that were recorded in this study did not exceed the values set by the ISO 2631-1 standards. The weighted RMS values of all nine types of heavy equipment were below 0.315 m/s², which is not uncomfortable (Table 1). Similarly, the VDV of the vehicles was below 8.5 m/s^1.75 and did not pose adverse health effects. Also, six of the nine machineries had significantly lower WBV values compared to the data gathered by Cann et al. (2003). For example, the forklift in the present study showed a VDV of 0.52 m/s^1.75, while in the above-mentioned study, it had a VDV of 3.35 m/s^1.75. The researchers also observed that among the 14 different types of heavy equipment measured in the Cann et al. (2003) study, the excavator had the second lowest RMS of 0.51 m/s² and a VDV of 5.76 m/s^1.75, while it showed the highest RMS value of 0.07 m/s² and a VDV of 1.77 m/s^1.75 in the present study. However, it should be noted that among the nine equipment types measured, there were five large excavators that were included in the sample that could have positively skewed the weighted average of the equipment’s WBV level.

Also, the environmental condition that this type of equipment was used for may have influenced the captured data. Excavators are mainly used to dig holes on rough terrain and move large amounts of earth that are oftentimes made of rock and hard materials, making WBV level more prevalent. However, in this study, the large excavator had one of the lowest values. This may be a result of the sites we surveyed. The soil at these sites was previously disturbed by excavators, making it either Class B or C soil. For instance, with WBV traveling through the coronal (y-axis) and vertical (z-axis) planes of the body, the compact roller had the highest RMS value of 0.5 m/s², and for the sagittal plane (x-axis), the forklift had a significantly high RMS value of 0.30 m/s² compared to the rest of the other equipment. The widely spread out high WBV levels for each orthogonal axis (x, y, z) could be attributed to factors such as the number of sampled vehicles, characteristics of terrain and materials, the operator’s driving characteristics, as well as the task the equipment was used to perform during data gathering. On the other hand, the large excavators having one of the lowest values for x-, y-, and z-axes could be due to the variance of the five samples.

Further, the age of construction equipment and its year of manufacture can be determinants as to its efficiency and safety. In the present study, the average age of the equipment surveyed was 6 years, which can be considered relatively new. Most construction tools are expected to last for 10,000 hours of usage, while others can go for 25,000 hours. Measurements reported by Paddan et al. (1999), the two studies completed by the National Research and Safety Institute (Boulanger, Donati, and Galmiche, 1996; Danie`re et al., 1987), and that of Cann et al. (2003) showed very high levels of WBV. The vibration data in the present study is much more within the ISO requirements. This may be because the present study took place 20 years after the latest of the four studies mentioned above. A lot has changed in construction equipment manufacturing since that time, and newer equipment is designed with better suspension methods of WBV levels. While this study still supports the claim that workers can be put at risk of injury when operating heavy equipment, there seems to be a much lower WBV risk using newer heavy equipment.

The highest prevalence of pain in the lower back (53%) was expected among the operators in this study. This is because they experienced vibration directly to the lower back area of the body and work in a seated position at an average operation of 8 hours per day. This finding agrees with that of the literature review on WBV and the risk of low back pain and sciatica (Burstrom, Nilsson, and Wahlstrom, 2014). The research revealed that exposure to WBV was associated with increased prevalence of low back pain and sciatica. Among professional truck drivers, it was found that MSD seem to be closely associated to exposure to WBV, mainly due to high prevalence and symptoms of low back pain (Moraes et al., 2016). Among professional drivers, physical demands, awkward postures, repetitive operations, as well as psychosocial loads showed a strong correlation with MSD in the lower back and, in some cases, the upper limbs (Bovenzi, 2010; Hoy et al., 2005; Miyamoto et al., 2000). In the present study, higher prevalence was also observed in the mid-back, neck, shoulder, and buttocks.

Vibration as a hazard does not necessarily or directly damage the musculoskeletal system. However, the combination of psychosocial and personal risk factors (e.g., age, weight, and BMI), awkward or static posture, and prolonged sitting can increase the risk of discomfort and pain. The operators had an average age of 47 years, an average weight of 91 kg, and an average BMI of 28.7 kg/m². This means that the heavy equipment operators examined in this study are at risk of developing MSD due to a possible combined effect of age, weight, BMI, and WBV exposure, as previously reported (Kumar, 2004). Our recorded data on age agrees with the trend of workers’ demographics in the US. Specifically, an aging workforce in the construction industry has been continuously recorded in previous decades (Schwatka, Butler, and Rosecrance, 2011). In case-control research, Palmer et al. (2008) suggested that exposure to WBV may not be the main cause of severe back pain; instead, the mental aspects and the perception of general health have more significant contributions with stronger association with the occurrence of low back pain in their sample.

One of the ways investigators suggested reducing exposure to WBV is through the education of operators. Langer et al. (2012) studied this recommendation among backhoe loaders. They found that a short education on vibration and jolts, proper seat adjustment, and awareness on the motion and speed of vehicles resulted in an average of 22.5% reduction in the WBV exposure. Among mining vehicle operators, researchers found that there is a need to develop more effective engineering controls, including better seat suspensions, to address non-vertical WBV exposures because these types of exposures can increase risks for adverse health effects, including MSD and impaired visual acuity (Kim, Marin, and Dennerlein, 2018). Minimizing the amount of WBV from the source to the operator is key to preventing acute and chronic exposures. Considering that operating heavy equipment in industries like construction requires prolonged sedentary positions, the damping and duration of effect of WBV need to be considered. Intervention emphasis may be put on the point of application to the body—the buttocks in the case of heavy equipment operators. Hence, much research was conducted to improve engineering designs of seats and tires of industrial vehicles (Dennerlein et al., 2022; Salmoni, Cann, and Gillin, 2010; Caffaro et al., 2017; Blood, Rynell, and Johnson, 2012). In a study that examined the key factors affecting low back pain due to WBV exposure using exploratory factor analysis and structural modeling, the researchers found that equipment and job-related organizational, personal, and social context factors are crucial in reducing low back pain due to WBV exposure (Vitharana and Chinda, 2019). The investigators further explained that seat type, specific training program, job rotation, worker satisfaction, and physical condition are crucial aspects in the reduction of low back pain symptoms related to WBV exposure.

The first limitation of the present study is the small number of heavy equipment vehicles and operators that were surveyed. It is necessary to confirm that newer models have lower WBV levels compared to the older ones. Therefore, a larger sample of construction vehicles for each type may provide a better representation of the WBV levels. Also, data was only collected from jobsites located in the northeast region of the United States, where there are differences in the environment, like the weather and terrain, as well as how work is generally completed. Next, the heavy equipment operators’ MSD levels are consistent with the findings from other studies. However, using a larger sample size of heavy equipment operators that allows an epidemiological study design can further test likelihood, cause and effect between variables, and minimize recall bias. It can provide a better insight as to the veracity of the effects of WBV on MSD symptoms development. However, there is no guarantee that these findings are representative of other construction vehicle models or the general population of construction operators’ MSD symptoms. Therefore, it is suggested that further investigations be made considering these limitations.

The present study is descriptive in nature and provides data on the levels of WBV of heavy equipment and the prevalence of MSD symptoms among the operators in the construction industry. After comparing the WBV levels for each of the nine types of construction vehicles to the 1997 ISO 2631-1 standards, it was confirmed that none resulted in overexposure. Although this finding is not a reason for concern, it does not confirm a similar trend with other equipment types and processes used in construction sites outside the northeast United States. The level of MSD prevalence of the surveyed operators was consistent with those of previously published studies. Specifically, low back pain was the most common condition reported by the surveyed construction operators. Other variables that can have potential effects on the occurrence of MSD symptoms are age, weight, BMI, and chronic exposure to WBV. The present study supports the claim that the aging workforce in the construction industry in the US is at risk of developing chronic physical health conditions such as MSD. These can be proliferated by other safety hazards, such as WBV. Therefore, more proactive and innovative approaches are necessary to minimize their exposure to various workplace hazards.

This research is supported by the New Hampshire IDeA Network of Biomedical Research Excellence (NH-INBRE) through an Institutional Development Award (IDeA), P20GM103506, from the National Institute of General Medical Sciences of the National Institutes of Health. The authors also extend their gratitude to the operators and their management for their participation in this study.

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