Mapping static and dynamic postures in seated operatives of vibrating mobile plant or vehicles

Outline of reasons and objectives
Prolonged exposure to whole-body vibration increases the risk of low-back pain problems. In France, 3 million mobile plant operatives who work in the sitting position may be exposed to this type of stress (drivers of tractors, bulldozers, excavators, forklift trucks, ride-on lawnmowers, etc.). The procedure for assessing vibration risks does not take account of the position of the body and of the movements related to doing a work task, even though those parameters are considered to be significant cofactors in the risk. To improve prevention in the field of vibration, INRS aims to incorporate postural constraints into the next revision of Standard ISO 2631-1:1997, and, in the longer term, aims to develop a combined posture and vibration assessment method.
In this context, the objectives of the study were to take vibration and posture measurements simultaneously at the driver stations of vibrating mobile plant for (1) identifying postural indicators relevant for distinguishing between types of plant, (2) estimating inter-individual differences in posture between operatives doing identical work tasks, and (3) assessing, under real conditions, the differences in posture between operatives for the main families of machines.

Approach
Vibration measurements were taken in compliance with Standard ISO 2631-1:1997. A seat pad accelerometer was placed on the seat of each of the vehicles. Posture measurements were taken in compliance with the recommendations of the standardised technical report ISO/TR 10687:2012 by means of the CUELA1 system developed by IFA2 . The angular differences of the segments of the body were compared with limit values derived from Standard EN 1005:2005 for evaluating working postures and movements.
The inter-individual posture variations were estimated by comparing measurements taken with 12 drivers on 3 construction vehicles (loader, dumper, and excavator) under controlled conditions.
125 measurements representative of the real exposure of the operatives were taken in companies for 13 families of plant.

Main results
This study made it possible to identify two distinguishing indicators for the static positions and for the movements.
Significant differences were observed between drivers doing identical work tasks. It was possible to attribute some of the differences to driving strategies that were common to several different vehicles.
Differences between the postures taken up by the drivers were observed depending on the vehicles both in the static positions and during the movements. Some of the differences were significant from the point of view of the procedure for evaluating the risk defined by Standard EN 1005:2005.

Discussion
The segments of the body and the movements that had the most significant differences relative to the reference positions were identified. The list of descriptive quantities for postures that is recommended by Standardised Technical Report ISO/TR 10687:2012 has thus been reduced for the families of vehicles measured.
The mapping of postures and of vibration will be continued as and when companies ask for assistance. Certain vehicles will studied as priorities (tractors, lawnmowers, forklift trucks, etc.). The research efforts should now focus on developing a severity criterion that takes posture and vibration into account simultaneously. For that purpose testing will be done in the laboratory under controlled conditions.