Whole body vibration exposure transmitted to drivers of heavy equipment vehicles: a comparative case according to the short- and long-term exposure assessment methodologies defined in ISO 2631-1 and ISO 2631-5

Citation: de la Hoz-Torres, M.L.; Aguilar, A.J.; Ruiz, D.P.; Martínez-Aires, M.D. Whole Body Vibration Exposure Transmitted to Drivers of Heavy Equipment Vehicles: A Comparative Case According to the Short- and Long-Term Exposure Assessment Methodologies Defined in ISO 2631-1 and ISO 2631-5. Int. J. Environ. Res. Public Health 2022,19, 5206. https:// doi.org/10.3390/ijerph19095206 Academic Editor: Paul B. Tchounwou Received: 21 March 2022 Accepted: 24 April 2022 Published: 25 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). International Journal of Environmental Research and Public Health Article Whole Body Vibration Exposure Transmitted to Drivers of Heavy Equipment Vehicles: A Comparative Case According to the Short- and Long-Term Exposure Assessment Methodologies Defined in ISO 2631-1 and ISO 2631-5 María L. de la Hoz-Torres 1, Antonio J. Aguilar 2,* , Diego P. Ruiz 2and Mª Dolores Martínez-Aires 1 1Department of Building Construction, University of Granada, Av. Severo Ochoa s/n, 18071 Granada, Spain; [email protected] (M.L.d.l.H.-T.); [email protected] (M.D.M.-A.) 2Department of Applied Physics, University of Granada, Av. Severo Ochoa s/n, 18071 Granada, Spain; [email protected] *Correspondence: [email protected] Abstract: The construction and transport sectors are the industries with the highest proportions of workers exposed to vibrations in the European Union. Heavy equipment vehicle (HEV) drivers often perform operations on different uneven surfaces and are exposed to whole body vibration (WBV) on a daily basis. Recently, a new version of ISO 2631-5 was published. However, since this new method required as input the individual exposure profile and the acceleration signals recorded on more surfaces, limited studies have been carried out to evaluate HEV operations according to this standard. The objectives of this study were to assess the WBV exposure using the methods defined in ISO 2631-1:1997 and ISO 2631-5:2018 and to compare the obtained health risk assessments between drivers with different anthropometric characteristics. For this purpose, two drivers were selected and a field measurement campaign was conducted. Regarding short-term assessment, results showed that VDV was the most restrictive method with exposure levels above the exposure action limit value, while SA d indicated that the same exposures were safe for the worker. With respect to long-term assessment, Risk Factor R A showed that the driver with the highest body mass index was the only one who exceeded the low probability limit of adverse health effects. Keywords: whole-body vibration; ISO2631-1:1997; ISO2631-5:2018; Heavy equipment vehicles 1. Introduction The second European Survey of Enterprises on New and Emerging Risk (ESENER-II) revealed that 70.9% of workers claim to be regularly exposed to physical agents at their workplace [ 1 ]. Among these agents, mechanical vibration is one of the physical risks to which workers are commonly exposed. However, statistically significant differences were found among sectors in relation to this exposure, with the highest proportions of workers exposed to vibration at least one quarter of the time being in the Construction and Transport sector (45%) and in the Agriculture and Industry sector (42%) [2]. In these industries, driving heavy equipment vehicles (HEV) exposed workers to whole-body vibrations (WBV) on a daily basis [ 3 – 7 ]. Vibrations are mainly transmitted to the driver’s body through the vehicle seat and the cabin floor [ 8 , 9 ]. In fact, since HEV drivers often perform activities on different types of surface (e.g., off-road, unpaved road, tarmac road, etc.), they are frequently exposed to higher levels of WBV and mechanical shocks [ 10 – 12 ]. The WBV exposure may last for long periods of time (6–7 h) during operations such as transport of materials, earth-moving, demolition processes, etc., and, therefore, it may involve a high risk to the worker’s health [13]. Several epidemiological studies have evidenced a relationship between long-term exposure to WBV and the occurrence of musculoskeletal disorders (MSDs), such as low back Int. J. Environ. Res. Public Health 2022,19, 5206. https://doi.org/10.3390/ijerph19095206 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2022,19, 5206 2 of 18 pain [ 14 – 16 ], sciatica [ 17 ], neck pain [ 18 , 19 ], degenerative changes in the lumbar spine [ 20 ], and other disorders such as cognitive/motor impairment. In fact, Costa et al. [ 21 ] found evidence of cognitive/motor impairment as a result of WBV exposure. MSDs are a cause of concern due to their impact on individual workers’ health, the social costs to European countries and the economic impacts on the enterprises [ 22 ]. Indeed, the first finding report published by the European Agency for Safety and Health at Work (EU-OSHA) about the ESENER 2019 reveals that MSDs are one of the biggest concerns for European workplaces [23,24]. In this context, the European Union defined minimum levels of worker protection to WBV exposure in order to control this risk in the workplace. Directive 2002/44/EC [ 25 ] states that the method to be used for the assessment of WBV exposure is the daily exposure A(8) or the highest vibration dose value (VDV), which are defined in the ISO 2631-1:1997 standard [ 26 ]. Directive 2002/44/CE also lays down the daily exposure action value (EAV) and the daily exposure limit value (ELV) for WBV exposure. However, the risk assessment in both methods and the limit values are limited to short-term exposure (over a day) and do not consider the cumulative effects of long-term WBV exposure. Since previous research has highlighted that cumulative exposure to WBV is one of the leading risks for the development of low back disorders [ 27 , 28 ], safety managers should be mindful of this constraint. Furthermore, the recent study conducted by Bovenzi et al. [ 29 ] pointed out that there is some evidence that the EU exposure limit values are excessive; so much so that WBV exposure beneath these limit values is associated with an elevated risk of low back pain. In addition, drivers with high body mass index (BMI) belong to the high-risk group, since previous research found that overweight and obesity increasing the risk of lumbar disc degeneration [30,31]. Nevertheless, there are other methods defined in ISO standards that can be applied in a complementary manner for the assessment of WBV exposure. In this case, since driving HEVs involves exposure to vibrations containing multiple shocks, the method defined in ISO 2631-5:2004 [ 32 ] may be considered as a complementary method to specifically assess this type of exposure. In contrast to ISO 2631-1, the method described in this standard includes the Factor R, which is used to assess the adverse health effects of long-term whole-body multiple-shock exposure and is calculated sequentially, taking into account the increasing age (and reducing strength) of the worker as the exposure time increases. This standard has recently been revised and the ISO 2631-5:2018 [ 33 ] has been released. This new version of the standard defines assessment methods that also include the posture and the anthropometric variables of the driver. Previous research has studied WBV exposure according to the methods defined in ISO 2631-1:1997 and ISO 2631-5:2004 [ 34 – 38 ]. Indeed, Eger et al. [ 39 ] pointed out a discrepancy regarding the presence of health risks and that the health guidance boundaries stated in ISO 2631-5:2004 had to be revised. In this context, the new version of the ISO 2631-5 published in 2018 has modified the model used to calculate the equivalent of compressive dose, but the health guidance boundaries remained the same as those previously defined in the 2004 version of this standard. However, very limited research has been conducted using the method defined in the ISO 2631-5:2018 standard due to the short time that has elapsed since its publication. Therefore, this study proposes to overcome this research gap. In this sense, the objective of this study is (1) to assess the risk associated with typical operations performed with a HEV, based on the methods defined in ISO 2631-1:1997 and 2631-5:2018; (2) to analyse the methods defined in the standards to determine whether the criteria predict the same level of health risk, and (3) to compare WBV exposure for two drivers with different anthropometric characteristics during operations performed on roads with different surface unevenness. Int. J. Environ. Res. Public Health 2022,19, 5206 3 of 18 2. Materials and Methods 2.1. Measurement of WBV and Field Test Participants were selected from a convenience sample of professional HEV drivers from companies in the study area. Two drivers were selected with experience in driving HEVs (both with more than 20 years of professional experience in this type of activity), which is especially relevant in the calculation of the adverse effects of cumulative exposure to WBV. In addition, the selected drivers had a significantly different BMI, so that the health effects under two different conditions could be compared (this is a characteristic considered in the method defined in ISO 2631-5:2018) (Table 1). The participants provided information on their work experience (first year of WBV exposure, daily—annual exposure duration and years of WBV exposure). Table 1. Characteristics of drivers. Driver D1 D2 Age 48 years 59 years Height 1.85 m 1.73 m Weight 120 kg 73 kg BMI 35.1 kg/m224.4 kg/m2 Mean daily exposure duration to WBV 4 h 4 h Mean annual exposure duration to WBV 150 days/year 150 days/year Age at first year of WBV exposure 20 years 20 years Exposure duration to WBV 28 years 39 years Posture Group (ISO 2631-5) 3 3 The HEV selected for the field test was a tractor. Both participating drivers are familiar with the operation of this type of vehicle. The vehicle characteristics are shown in Table 2. According to Regulation No. 167/2013 of the European Parliament and of the Council [ 40 ], this vehicle is classified as Class II Category A. Table 2. Characteristics of the vehicle. Dimensions Characteristics Weight 3800 kg Power 78 kW Wheelbase 2.26 m Cylinder 4 Length 4.19 m Front tyre 7.50-18 Width 2.05 m Rear tyre 13.6R38 Height (cab) 2.26 m The field test was carried out in Porcuna (Spain) (37 ◦ 52 0 11 00 N, 4 ◦ 11 0 14 00 W). Prior to the definition of the test, several drivers of this type of vehicle working in the area were interviewed. Based on the obtained information, a typical work cycle for this type of driver was identified. As a result of this process, a route was selected for the field test. The selected route was representative of the complete work cycle and comprises different types of surfaces. Previous studies have shown that the magnitude of WBV transmitted to the driver is influenced by the characteristics of the road surface [ 41 – 43 ]. The route layout and the different surfaces are shown in Figure 1. The route had a length of 10.5 km , comprising 1.5 km off-road, 3 + 2.5 km of unpaved road (two different types were considered) and 3.5 km of tarmac road. The sections of each type of surface were selected to obtain a representative sample of WBV exposure during a working day. This experimental design has been used in previous studies about WBV exposure assessments [9,34,39,44]. Int. J. Environ. Res. Public Health 2022,19, 5206 4 of 18 Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 4 of 18 Figure 1. Route selected for field test. Several operational aspects were considered prior to the start of the field test. Tractors are widely used in different operations and these activities often require the use of interchangeable towed machinery or a trailer. In this research, the tractor used a trailer while the measurements were being carried out. Another important aspect considered was the speed. Two factors were considered in order to set the speed limits during the performance of the field test: the maximum forward speed according to the surface conditions and the maximum legal speed allowed for the vehicle on the road. Therefore, in order to characterise the speed on each surface, an experimental campaign was carried out prior to the field test. The obtained results are shown in Figure 2. On the basis of the above criteria, in the case of off-road driving, the unevenness of this surface requires a limited speed to be maintained in order to ensure the safety of the driver. Consequently, the speed limit was set between 5 and 10 km/h on this type of surface. On unpaved roads, the speed range increases as the surface is more regular than in the previous case. However, since these types of roads can have a wide variety of roughness conditions, this category was divided into two: unpaved road I (high roughness surface), where the speed ranges between 10 and 15 km/h, and unpaved road II (low roughness surface), where the speed ranges between 15 and 25 km/h. Finally, the mean forward speed of the tractor on tarmac roads is higher than on other surfaces (from 20 to 25 km/h). Figure 1. Route selected for field test. Several operational aspects were considered prior to the start of the field test. Tractors are widely used in different operations and these activities often require the use of interchangeable towed machinery or a trailer. In this research, the tractor used a trailer while the measurements were being carried out. Another important aspect considered was the speed. Two factors were considered in order to set the speed limits during the performance of the field test: the maximum forward speed according to the surface conditions and the maximum legal speed allowed for the vehicle on the road. Therefore, in order to characterise the speed on each surface, an experimental campaign was carried out prior to the field test. The obtained results are shown in Figure 2. On the basis of the above criteria, in the case of off-road driving, the unevenness of this surface requires a limited speed to be maintained in order to ensure the safety of the driver. Consequently, the speed limit was set between 5 and 10 km/h on this type of surface. On unpaved roads, the speed range increases as the surface is more regular than in the previous case. However, since these types of roads can have a wide variety of roughness conditions, this category was divided into two: unpaved road I (high roughness surface), where the speed ranges between 10 and 15 km/h, and unpaved road II (low roughness surface), where the speed ranges between 15 and 25 km/h. Finally, the mean forward speed of the tractor on tarmac roads is higher than on other surfaces (from 20 to 25 km/h). However, it should be noted that the legal speed limit for tractors is 25 km/h when using a trailer or interchangeable towed machinery. Int. J. Environ. Res. Public Health 2022,19, 5206 5 of 18 Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 5 of 18 However, it should be noted that the legal speed limit for tractors is 25 km/h when using a trailer or interchangeable towed machinery. Figure 2. Mean speed of displacement according to type of surface. Once the field test procedures were defined, each driver repeated the pre-defined route three times. The test was carried out on weekdays between 8:00 and 10:00 to ensure homogeneous traffic conditions. The set of conditions was the same for the two drivers in order to compare the WBV exposure associated with activities with the same extrinsic factors (including same type of surface, vehicle and forward speed). 2.2. Analysis of WBV Exposure The methods defined in ISO 2631-1:1997 and ISO 2631-5:2018 have been applied in this study in order to assess the level of WBV exposure. Since the aim of this study is to analyse the prediction of health risk associated with HEV activities, methods that assess other types of activities (e.g., high speed marine craft operations) or use other evaluation criteria (e.g., comfort) have not been considered. The procedures of both standards are described in the following sections. 2.2.1. ISO 2631-1:1997 The ISO 2631-1:1997 standard defines the root mean square value A(8) method and the Vibration Dose Value (VDV) method. The A(8) is calculated based on the weighted root mean square acceleration (rmsw). The rmsw value of the weighted acceleration was calculated according to Equation (1). The VDV is calculated based on the fourth power of the weighted acceleration. The vdvw value of the weighted acceleration was calculated according to Equation (2). a= 󰇯1 Ta (t)dt  󰇰/ (1) vd v =󰇯a (t)dt  󰇰/ (2) where aw is the weighted acceleration at time t (ms−2) and T is the duration of the measurement (s). The frequency weighting filter Wd is used for the x and y axes, and the Wk is used for the z axis. Figure 2. Mean speed of displacement according to type of surface. Once the field test procedures were defined, each driver repeated the pre-defined route three times. The test was carried out on weekdays between 8:00 and 10:00 to ensure homogeneous traffic conditions. The set of conditions was the same for the two drivers in order to compare the WBV exposure associated with activities with the same extrinsic factors (including same type of surface, vehicle and forward speed). 2.2. Analysis of WBV Exposure The methods defined in ISO 2631-1:1997 and ISO 2631-5:2018 have been applied in this study in order to assess the level of WBV exposure. Since the aim of this study is to analyse the prediction of health risk associated with HEV activities, methods that assess other types of activities (e.g., high speed marine craft operations) or use other evaluation criteria (e.g., comfort) have not been considered. The procedures of both standards are described in the following sections. 2.2.1. ISO 2631-1:1997 The ISO 2631-1:1997 standard defines the root mean square value A(8) method and the Vibration Dose Value (VDV) method. The A(8) is calculated based on the weighted root mean square acceleration (rms w ). The rms w value of the weighted acceleration was calculated according to Equation (1). The VDV is calculated based on the fourth power of the weighted acceleration. The vdv w value of the weighted acceleration was calculated according to Equation (2). aw=  1 T T Z 0 a2 w(t)dt  1/2 (1) vdvw=  T Z 0 a4 w(t)dt  1/4 (2) where a w is the weighted acceleration at time t (ms −2 ) and T is the duration of the measurement (s). The frequency weighting filter W d is used for the x and y axes, and the W k is used for the z axis. The value of the daily exposure normalised to 8 h for method A(8) and VDV is calculated according to Equations (3) and (4), respectively. A(8)=kx,y,z∗rmswsTexp T0 (3) Int. J. Environ. Res. Public Health 2022,19, 5206 6 of 18 VDV =kx,y,z∗vdvw4 sTexp Tmeas (4) where k denotes the multiplication factor defined for each axis (k x,y =1.4 and k z = 1), T exp is the measurement duration, T 0 is the reference duration of 8 h, and T meas is the daily duration of vibration exposure. 2.2.2. ISO 2631-5:2018 This standard defines two exposure regimes: one for severe conditions and one for less severe conditions. In this research, the less severe conditions method has been used for the assessment of WBV exposure. This method is indicated for exposures to WBV without free-fall events and where the subject remains seated throughout the measurement. This method uses as input the acceleration measured (x, y and z axes) at the seat surface (minimum). However, accelerations measured at the backrest, feet and hands can also be used. These accelerations are used to calculate the compressive force between the vertebrae from transfer functions of a biomechanical model. These transfer functions depend on the posture, body mass and body mass index (BMI) of the driver. In addition, the method needs to include the historical vibration exposure (first and last year of exposure, exposure pattern per day and year). The S A (MPa) compression dose is calculated for each disc level of the lumbar spine (T12/L1, L1/L2, L2/L3, L3/L4, L4/L5 and L5/S1, see Figure 3) according to Equation (5): SA="∑ iCdyn,i B6#1/6 (5) where C dyn,I (N) is the sum of the peak compressive forces acting on the vertebral endplate and B (mm 2 ) is the area of each disc level of the lumbar spine (T12/L1 = 1460 mm 2 , L1/L2 = 1520 mm2 , L2/L3 = 1580 mm 2 , L3/L4 = 1590 mm 2 , L4/L5 = 1600 mm 2 and L5/S1 = 1550 mm2). The equivalent daily compressive dose SA d (MPa) of the lumbar spine is calculated with Equation (6): SA d= ∑ j SA6 j td,j tm,j !1/6 (6) where SA j is the dynamic compressive stress of the lumbar spine due to vibration exposure to condition j, t d,j is the time period of the daily vibration exposure to condition j and t m,j is the time period over which SA jhas been measured. Finally, the risk factor RAfor each disc level is calculated according to Equation (7): RA=  n ∑ i=1 SA dN1/6 i SA u,i −SA stat,i !6  1/6 (7) where SA d is the constant daily compressive dose; i is the year counted; N i is the number of exposure days per year i; n is the number of exposure years; SA u,i is the ultimate strength of a lumbar vertebra in a person of age (b + i) years, with b being the age at which the exposure started; SA stat,i is the mean value of the compressive-decompressive force divided by the area of a vertebra endplate B (mm2) for year i. SA u,i is calculated according to Equation (8): SA u,i =6.765024 MPa −0.067184 (b+i)(8) Int. J. Environ. Res. Public Health 2022,19, 5206 7 of 18 Int. J. Environ. Res. Public Health 2022, 19, x FOR PEER REVIEW 7 of 18 exposure started; S,  is the mean value of the compressive‒decompressive force divided by the area of a vertebra endplate B (mm 2 ) for year i. S,  is calculated according to Equation (8): S, =6.765024 MPa − 0.067184 (b i) (8) Figure 3. Disc level of the lumbar spine. 2.2.3. Health Guidance Caution Zone (HGCZ) Table 3 shows the limits stated in Directive 2002/44/EC for an eight-hour exposure reference period. ISO 2631-5:2018 defines the limits for the probability of an adverse health effect of exposure to vibration. Table 3. Health guidance caution zone. ISO 2631-1:1997 / Directive 2002/44/EC ISO 2631-5:2018 Exposure Limit Values and Action Value Probability of an Adverse Health Effect Exposure Action Value (EAV) A(8) = 0.50 ms −2 VDV = 9.10 ms −1.75 Low S  < 0.50 MPa R < 0.80 Moderate S  > 0.50 MPa R > 0.80 Exposure Limits Value (ELV) A(8) = 1.15 ms −2 VDV = 21.00 ms −1.75 S  < 0.80 MPa R < 1.20 High S  > 0.80 MPa R > 1.20 Figure 3. Disc level of the lumbar spine. 2.2.3. Health Guidance Caution Zone (HGCZ) Table 3shows the limits stated in Directive 2002/44/EC for an eight-hour exposure reference period. ISO 2631-5:2018 defines the limits for the probability of an adverse health effect of exposure to vibration. Table 3. Health guidance caution zone. ISO 2631-1:1997/Directive 2002/44/EC ISO 2631-5:2018 Exposure Limit Values and Action Value Probability of an Adverse Health Effect Exposure Action Value (EAV) A(8) = 0.50 ms−2VDV = 9.10 ms−1.75 Low SA d< 0.50 MPa RA< 0.80 Moderate SA d> 0.50 MPa RA> 0.80 Exposure Limits Value (ELV) A(8) = 1.15 ms−2VDV = 21.00 ms−1.75 SA d< 0.80 MPa RA< 1.20 High SA d> 0.80 MPa RA> 1.20 2.3. Measurement Equipment The SV38 (SVANTEK) tri-axial seat pad accelerometer was used to measure the acceleration transmitted between the seat and the driver. This accelerometer measures the signal in the x- (front-to-rear), y- (left-to-right) and z- (buttocks-to-head) axes. The acceleration signal was recorded according to the ISO 2631-1:1997 and ISO 2631-5:2018 standard. Additionally, the position of the vehicle was registered by a Global Positioning System (GPS). The signals were post-processed with Matlab®software (MathWorks, Natick, MA, USA). Int. J. Environ. Res. Public Health 2022,19, 5206 8 of 18 3. Results 3.1. Analysis According to ISO 2631-1:1997 and Directive 2002/44/EC The results obtained using the methods defined in ISO 2631-1:1997 for driver 1 and 2 are shown in Tables 4and 5, respectively. Table 4. Summary of data obtained from driver 1 according to ISO 2631-1:1997, method A(8). Surface No. rmswx (ms−2) rmswy (ms−2) rmswz (ms−2) A(8) ——- A(8) S1 #1 0.51 0.39 0.49 0.50 0.43 #2 0.41 0.33 0.47 0.41 #3 0.39 0.30 0.45 0.38 S2 #1 0.37 0.38 0.59 0.42 0.44 #2 0.37 0.38 0.61 0.43 #3 0.36 0.41 0.67 0.48 S3 #1 0.36 0.39 0.66 0.47 0.43 #2 0.35 0.40 0.62 0.44 #3 0.32 0.34 0.54 0.38 S4 #1 0.18 0.21 0.38 0.27 0.26 #2 0.14 0.19 0.36 0.25 #3 0.14 0.21 0.36 0.26 Table 5. Summary of data obtained from driver 2 according to ISO 2631-1:1997, method A(8). Surface No. rmswx (ms−2) rmswy (ms−2) rmswz (ms−2) A(8) ——- A(8) S1 #1 0.48 0.43 0.63 0.47 0.55 #2 0.40 0.35 0.38 0.40 #3 0.79 0.65 0.56 0.78 S2 #1 0.36 0.41 0.73 0.51 0.52 #2 0.39 0.46 0.47 0.45 #3 0.42 0.59 0.52 0.58 S3 #1 0.33 0.34 0.58 0.41 0.46 #2 0.37 0.42 0.40 0.41 #3 0.47 0.55 0.52 0.54 S4 #1 0.22 0.25 0.40 0.28 0.37 #2 0.27 0.42 0.37 0.42 #3 0.20 0.41 0.29 0.40 * Bold numbers indicate that the value is higher than the EAV. From these results, it can be observed that operations on the S1, S2 and S3 surfaces provide the highest exposure dose for both drivers. It should be noted that, in the case of driver 2, the exposure dose on surfaces S1 and S2 exceeds the EAV limit value stated in Directive 2002/44/EC (A(8) = 0.5 ms−2). Regarding the VDV method, Tables 6and 7show the results obtained on each type of surface for both drivers. Int. J. Environ. Res. Public Health 2022,19, 5206 9 of 18 Table 6. Summary of data obtained from driver 1 according to ISO 2631-1:1997, method VDV. Surface No. vdvwx (ms−2) vdvwx (ms−2) vdvwx (ms−2) VDV ———- VDV S1 #1 3.21 2.44 3.56 11.53 9.88 #2 2.27 1.92 3.33 9.27 #3 2.36 1.83 2.90 8.82 S2 #1 1.99 1.96 2.95 8.93 9.32 #2 1.94 1.89 2.89 8.92 #3 1.89 1.88 3.12 10.11 S3 #1 2.17 2.41 3.63 10.20 9.43 #2 2.02 2.32 3.36 9.60 #3 1.81 1.99 2.97 8.48 S4 #1 1.01 1.18 2.14 5.55 5.33 #2 0.78 1.07 1.99 5.22 #3 0.79 1.16 2.00 5.23 * Bold numbers indicate that the value is higher than the EAV. Table 7. Summary of data obtained from driver 2 according to ISO 2631-1:1997, method VDV. Surface No. vdvwx (ms−2) vdvwy (ms−2) vdvwz (ms−2) VDV ———- VDV S1 #1 3.00 2.68 3.92 11.16 12.78 #2 2.69 2.23 3.63 9.32 #3 4.52 3.61 3.05 17.85 S2 #1 2.61 3.21 5.74 12.90 12.01 #2 1.94 2.46 2.43 10.40 #3 3.81 5.06 5.15 12.73 S3 #1 2.44 2.60 4.30 9.33 10.45 #2 2.42 2.86 2.41 10.20 #3 3.51 4.00 4.76 11.81 S4 #1 2.02 2.10 3.82 8.20 9.01 #2 2.00 3.00 2.48 9.54 #3 1.34 2.40 1.56 9.28 * Bold numbers indicate that the value is higher than the EAV. In the case of both drivers, as well as the results obtained from the A(8) method, the level of WBV transmitted is higher on those surfaces with the highest unevenness. The results show that on three surfaces (S1, S2 and S3), the EAV limit established in Directive 2002/44/EC (VDV = 9.1 ms−1.75) is exceeded. The comparison of the WBV assessment provided by both methods, considering each driver and each type of surface, shows that driver 2 has a higher exposure dose than driver 1. According to the results obtained from method A(8), driver 1 was exposed below the HGCZ limits, while driver 2 was exposed above the HGCZ limits for surfaces S1 and S2. In the case of the VDV method, both drivers exceed the EAV limit on all the surfaces except the tarmac road. 3.2. Analysis According to ISO 2631-5:2018 This section shows the results obtained using the less severe method defined in ISO 2631-5:2018. The results of the equivalent daily compressive dose SA d for each disc level of the lumbar spine are shown in Tables 8and 9for driver 1 and 2, respectively. Int. J. Environ. Res. Public Health 2022,19, 5206 16 of 18 Informed Consent Statement: Not applicable. Data Availability Statement: Data are provided upon request to the corresponding author. Acknowledgments: The first two authors wish to acknowledge the support of the Ministerio de Ciencia, Innovación y Universidades of Spain under an FPU grant. Conflicts of Interest: The authors declare no conflict of interest. References 1. Irastorza, X.; Milczarek, M.; Cockburn, W. Second European Survey of Enterprises on New and Emerging Risks (ESENER- 2): Overview Report: Managing Safety and Health at Work. Publications Office of the European Union. 2016. Available online: https://osha.europa.eu/en/publications/second-european-survey-enterprises-new-and-emerging-risks-esener- 2-overview-report (accessed on 10 March 2022). 2. 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