Variability in humans, machines and tasks on whole-body vibration exposures and effects

There are many factors that can influence the effectiveness of any risk management strategy, in the case of whole-body vibration exposure many problems are faced with the quantification of risk, measurement of risk and subsequent risk reduction. The quantification of vibration effects is equally as complex as the quantification of vibration itself. Exposure to whole-body vibration (WBV) causes a distribution of motions and forces within the human body and to complicate matters the transmission of vibration to the body is also dependent on body posture. To-date there has been little attempt to accurately reflect many of the typical postures and vibration environments experienced by operators of earth moving machines in a laboratory setting. The overall aim of the thesis was to determine the variability between humans, machines and task environments in order to provide knowledge to inform improvements in methods of risk management for whole-body vibration exposure. The field measurement phase of the research focused on characterising features of whole-body vibration exposure among operators of earthmoving machines throughout a range of industry sectors. Some of the biggest industries; coal mining, quarries, and construction were targeted to obtain data on the types of machines for which very little was previously available. Research was carried out under real operating conditions to investigate the nature of occupational exposure to whole-body vibration and to determine the causes of variability between measurements. The laboratory phase of the research simulated the conditions of the 'real working environment' observed in the field study in order to examine how twisted non-neutral postures could influence the biomechanical, performance and workload responses of humans. The machines with the greatest vibration emission were generally those that spent most of their time tracking. The worst machine for vibration exposure was a challenger 85D tracked tractor towing a 'hex' attachment. Operators of this machine would exceed the EU Physical Agents Exposure Limit Value in about 2.5 hours. The next most severe earth moving machines were bulldozers and tracked loaders and with long working hours typically observed in industry some of these machines would also exceed the ELV in a working day. The influence of variability between work cycles was found to be a particular problem for the bulldozer and excavator machines, variation between work cycles exceeded the 25% variance limit criteria. If these machines were targeted for a WBV health risk assessment then the measurement durations will need to take account of this variation in the extrapolation to an 8-hour exposure. The operators of these tracked machines were also found to adopt non-neutral twisted postures during reversing manoeuvres. The twisted posture adopted by the bulldozer and tracked loader operators was recreated in the laboratory. Findings demonstrated that operators are likely to be putting their necks in a vulnerable position in the twisted posture due to the large increase in rotational movement at the head during exposure to vibration. Decrements in reaction time performance and increases in workload were also found while individuals were sat in a twisted posture and exposed to vibration.