Dinesh Mohan and Puneet Mahajan
Objectives
Ergonomic analysis of tractor controls. Measurement and evaluation of tractor vibration and developing counter measures. Biomechanical study to evaluate deleterious effects of vibrations on health of tractor operators.
Methodology
Analysis of location of tractor controls and force required to operate them with a view for optimisation for Indian conditions. Measurement of vibration at different interfaces and simulating on computer model. Isolation and mitigation solutions for vibration will be developed for different interfaces. Physiological impairment of tractor operators will be compared with control group using medical investigations and computer modeling. Solutions will be suggested to minimize the whole body vibration.
Conclusion
The Indian tractor driving farmers are subjected to whole body vibrations which exceed ISO 2631-1 (1985) health limits and "health caution zone" upper limits of ISO 2631-1 (1997) as shown by our experimental measurements and mathematical modeling. The tractor-driving farmers have significantly higher low back pain complaints than non-tractor driving farmers control group. However, MRI examination of the study group and the control group did not reveal any significant difference in degenerative changes between the two groups. The significant finding of this study are listed below.
The tractor seat vibration power spectral densities were maximum in 1-10 Hz frequency range for both calculated and measured values.
Comparisons of measured as well as calculated rms accelerations with ISO 2631-1 (1985) indicate that severity of vibration as 8-hour "exposure limits" on all terrain-tractor combinations were exceeded. When evaluated according to the ISO 2631-1 (1997) standard for both measured and calculated values, 8-hour working exceeded the upper limit of "health guiding caution zone".
The rms accelerations calculated from mathematical model with ISO 5008 track were higher as compared to measured values on farm and non-farm terrains. Therefore, in absence of experimental data the model with ISO 5008 (1979) smooth track can be safely used to predict severity of vibrations for tractors with respect to existing ISO health limits.
There was a statistically higher incidence of reported low back pain among tractor driving farmers as compared to non-tractor driving farmers. But there was no objective difference between the two groups as assessed by clinical evaluation.
Magnetic Resonance Imaging evaluations did not reveal any significant difference either in lumbar intervertebral disc degeneration or lumbar facet arthropathy between tractor driving farmers and non-tractor driving farmers.
No specific objective cause could be attributed to the symptoms of backache as described by the tractor driving farmers by either clinical or Magnetic Resonance Imaging evaluation.
Overall abnormal MRI findings of 96% at any level in both the groups were much higher than those reported earlier, though the reported incidence of low back pain was low.
It is possible that whole body vibrations experienced by the tractor driving farmers do contribute to a higher incidence of reported low back pain, but the site of origin of the pain or the associated factors are not identifiable by MRI and clinical evaluation.
The health standards need to be based on operator’s perception of pain rather than detectable tissue degeneration until the evolution of better diagnostic methods and the ride characteristics of Indian tractors need to be improved to reduce the vibrations experienced by drivers.
