Strain caused by whole-body vibration increases when unfavourable body postures are adopted at the same time. This relationship is described qualitatively in epidemiological studies, and is also mentioned in the code of practice for formally recognized occupational disease (BK) No 2110. However, no quantitative relationship has yet been recorded between measured values of stress owing to vibration and body posture on the one hand and occupational medical findings (strain data) on the other.
The aim of the present project was to develop, in a dissertation based upon DGUV research project FF-FP0306, an assessment procedure for combined exposure to whole-body vibration and unfavourable body posture, which were collected quantitatively by field measurements.
The stresses caused by unfavourable body postures and vibration were measured representatively for a shift on 58 test subjects (IFA). For 102 test subjects in the same companies, functional diagnostic tests were also conducted and questionnaires completed concerning mental hazards and general information (RWTH). For 31 test subjects, both measurements and test results were available. During the DGUV research project FF-FP0306, the Institute of Occupational Medicine of the RWTH Aachen recorded strain data by methods including functional diagnostic tests according to the "Fokus" method. Altogether, a maximum of 200 drivers (of buses, locomotives, (gantry) cranes, earthmoving machinery, forklift trucks) exposed to vibration in a number of companies were to be studied. As a partner in this study, the IFA measured the stress of whole-body vibration and unfavourable body posture.
Several variables intended to describe the stress are discussed in the literature both for whole-body vibration and for body postures (daily vibration exposure A(8), evaluation of static working postures to ISO 11226, etc.). The same applies to the strain (affected individuals' own descriptions of complaints, the "Fokus" method, etc.). In order for an assessment method to be developed from these variables, the variables must be selected that best describe the relationship between the stress and the strain. The various variables were therefore subjected to a statistical analysis in order for a suitable assessment method to be created for the combined exposure. The assessment was performed for 102 test subjects for whom strain data were available. The stress data for whole body vibration and body postures measured on 58 test subjects were transferred to comparable workplaces in the same companies.
Owing to the small study population, an attempt was first made to compare specific stress variables with strain variables, in order to determine which variables exhibit the best correlation. It was found that of the strain variables, the affected individuals' own statements regarding the incidence of back pain in the preceding year and the number of days of unfitness for work owing to back complaints yielded the best correlations.
The stress is best described by the following variables: the daily vibration exposure value A(8), the number of body angles lying within the non-neutral range for over 30% of the exposure duration ((R) DOF), and information on heavy lifting and carrying provided by the affected individuals themselves. In the final step, an attempt was made to derive a statistical model for the stress in a logistic regression from all variables. The A(8) and (R) DOF were the only stress variables that described the incidence of back pain in the preceding year with statistical significance. The stress variables were input into the equation in linear form. No additional effect resulting from combination of the stress variables was observed. This also meant that values with a linear dependency upon A(8) and (R) DOF also permitted a significant description of the stress. This was tested successfully on two examples discussed in the literature. It was thus possible to describe the stress-strain relationship in quantitative terms, and verified variables were produced for the assessment of stresses in companies.
-cross sectoral-Type of hazard:
work-related health hazards, noise/vibrationsCatchwords:
epidemiology, load, vibrationDescription, key words:
Epidemiology, field measurements, mixed exposures, whole-body vibration, posture