User-centred design for civil construction: optimising productivity by reducing safety and health risks associated with the operation and maintenance of on-road vehicles and mobile plant.

A range of productivity implications, injury and health risks are associated with the operation and maintenance of road construction equipment. Potential unwanted events giving rise to these risks include: slip, trips and falls from ground or at height; performance of hazardous manual tasks; exposure to heat, chemicals and whole body vibration; vehicle roll overs; and collisions. It may be possible to remove or reduce the risk of these events through improved design of the equipment and wider organisational systems. Design analysis techniques and a risk assessment tool (Design OMAT and EDEEP) were applied in the review of an asphalt job truck. Findings have led to preliminary design considerations for improvement and there are implications for organisational system change

Measuring and managing workplace whole-body vibration exposures

An overview of recent research in the area of whole-body vibration measurement and management is provided. Prolonged exposure to high amplitude whole-body vibration is associated with a range of adverse health effects, particularly back pain. Operators of a range of workplace plant and equipment are exposed to the hazard. ISO2631.1 describes frequency weightings to be applied to accelerometer data and describes measures for describing vibration amplitude. An iOS application is available which may facilitate routine measurement of whole-body vibration at workplaces as a means of identifying and evaluating opportunities to reduce vibration amplitudes. Modifiable factors associated with occupational whole-body vibration exposure include the environment in which equipment is operated including roadway design and maintenance; the tasks performed using the equipment; the design of equipment including suspension and seat; equipment condition including maintenance of suspension and seating; and operator behaviour, especially speed of travel for many vehicles

Control measures for avoiding collisions in underground mines

Collisions between vehicles, and between people and equipment, are a high risk in underground mines, and particularly coal mines. The consequences include serious injury and fatalities. The prevention of collisions has recently been a focus of attention by regulators in NSW and Queensland; and particularly the promotion of technological solutions for alerting equipment operators to the proximity of other vehicles, equipment, or people. This paper examines reports describing fatal underground collisions occurring in coal mines in the USA to determine the likely benefit of a range of control measures. All fatalities involving collisions in underground coal mines in the USA ocurring since the year 2000 were identified (n=41). Restricted visibility is implicated as a causal factor in many fatalities, suggesting that control measures such as the provision of video cameras, and proximity detection linked to warning tones, may be effective barriers in some situations. However, in more than half the fatalities, the person operating the equipment was killed, or the operator of the equipment was aware of the location of the person who was killed. In these situations, provision of video cameras, or proximity detection linked to a warning tone alone, may not be sufficient. A series of mini-case studies adapted from the public domain reports of these fatalities are presented to illustrate the issues

PREFERRED GAZE ANGLE AND VERGENCE DEMANDS Visual Display Height

Many workstations require fixation on relatively close visual targets, such as computer displays. These visual targets should be located at least 15° below horizontal eye level. The argument for lower visual targets commences with the observation that subjective preference is for visual targets to be located such that the eyes are rotated downwards relative to the head. A mechanical mechanism for this phenomenon has been proposed based upon the knowledge that an observer must converge to maintain single vision of near visual targets. This ocular vergence is produced by activation of the medial recti muscles of the eye. However, the extraocular muscles that raise the eyes (the superior recti and inferior obliques) also create a horizontal divergent force. Raising the eyes thus increases the activation required of the medial recti which causes visual discomfort. This simple mechanical model explains why observers prefer to look downwards to view near targets, and why the preferred vertical gaze angle gets progressively lower for closer objects. Measurements of open loop heterophoria (an indirect measure of vergence effort) as a function of vertical gaze angle are consistent with these conclusions INFLUENCE OF TARGET LOCATION ON GAZE ANGLE AND POSTURE In a normal erect posture, the ear-eye line is typically about 15° above the horizontal. Consequently, for a seated observer to fixate a visual target placed at horizontal eye height, either the preferred gaze angle must be compromised (leading to increased vergence effort) or the head rotated posteriorly by some combination of atlanto-occipital or cervical extension. It has been demonstrated experimentally that changing the height of visual targets results in changes in both gaze angle and head orientation, and the changes in head orientation associated with changes in vertical target location are achieved predominantly by changes in atlanto-occipital posture. Gaze angles higher than preferred were adopted when the visual target was higher than 15° below horizontal eye level ATLANTO-OCCIPITAL AND CERVICAL BIOMECHANICS Interpretation of the consequences of the observed postural responses requires consideration of the biomechanics of the head and neck. The head and neck system comprises a rigid head located above a relatively flexible cervical spine. Flexion and extension are possible at the atlanto-occipital and cervical joints. The ligaments and joint capsules are relatively elastic, especially within the mid-range, and a large range of movement is possible without significant contribution from passive tissues. The centre of mass of the head, and the head and neck combined, is anterior to the atlantooccipital and cervical joints. Consequently, extensor torques about the atlanto-occipital and cervical joints are required to maintain static equilibrium when the trunk is vertical. A large number of muscles with diverse sizes, morphology and attachments are capable of contributing to these torques. The suboccipital muscles, which have origin on C1 and C2 and insert on the occipital bone, are capable of providing extensor torque about the atlanto-occipital joint only; others (such as semispinalis capitis) provide extensor torque about cervical as well as the atlanto-occipital joints; while others provide extensor torque about cervical vertebrae only. Increased flexion at the atlanto-occipital joint increases the horizontal distance of the center of the mass of the head from its axis of rotation (level with the mastoid process). Similarly, when the trunk is approximately vertical, an increase in flexion of the cervical spine increases the horizontal distance of the center of the mass of the head and neck combined from the axes of rotation in the vertebral column (and all else remaining the same, the horizontal distance of the head from its axis of rotation). Hence, with th