WHOLE BODY AND ARM-HAND VIBRATION MONITORING
Whole body vibration (and high amplitude jolts and jars – shock) is known to be a contributing factor to muscle fatigue, stiffness, lower back pain and serious physical injury.
Workforce Health conducts whole body vibration assessments on mining and transport plants each year with a vibration dosimeter (with simultaneous floor and seat tri-axial accelerometers) to measure exposure levels to determine compliance with the recommended levels in South African Standards.
WHAT ARE THE ASSOCIATED WHOLE BODY VIBRATION HEALTH EFFECTS?
The health effects that are associated with long term exposure to Whole Body Vibration encompasses:
Back injury, especially spinal injuries.
Joint and muscle stiffness.
Damage to female reproductive system.
Changes in the balance and vision of workers.
Changes in the Respiratory, Endocrine, cardiovascular & digestive systems.
While not a direct health effect from Whole Body Vibration, the difficulty in a task can be increased through poor vision, hand-eye coordination and concentration which may make a task more hazardous. For instance the conditions of roads or observing hazards may be masked due to the vibration, thereby being one significant cause in a workplace accident.
There is also an association in increased risk of manual handling injuries, particularly back injuries, due to exposure of Whole Body Vibration. This is due to the vibration fatiguing muscles and weakening them over time which increased the risk of putting the back out of place. Reducing vibration will place less stress and strain on back muscles so they can work more effectively in preventing injury.
Health surveillance may assist to prevent the Whole Body Vibration and associated manual handling injuries by increasing working health and awareness of risk factors.
MEASURING WHOLE BODY VIBRATION
Whole body vibration is measured through the use of an accelerometer that is placed within a seat pad. The seat pad which, the operator sits on vibrates in rhythm of the worker operating the equipment. The three plane vectors are measured in the x, y & z coordinates and averaged to determine the Whole Body Vibration levels.
The Whole Body Vibration testing is reported in terms of m/s2, being a measurement of acceleration and is the Roo Mean Square (RMS) value. The measurements are also filtered to assess only specific frequencies that the body is responsive to. In general the frequencies for Whole Body Vibration are much lower than that which has a significant health impact compared to the weighted frequencies for Hand Arm Vibration (HAV).
As well as the seat being measured for Whole Body Vibration, an additional accelerometer may be used to measure the chassis of the equipment. This testing is used to determine the vibration that is absorbed by the seat. Most seats these days will have cushioning and also adjustable tension to ensure that maximum vibration reductions can be achieved.
Each task that the worker undertakes on the equipment is tested for the RMS vibration and is then also assessed in terms of the duration of the task. The tasks that are conducted over the length of the day are then added to evaluate the overall daily Whole Body Vibration exposure.
Another parameter is also used in Whole Body Vibration assessments which is the Vibration Dose Value (VDV) which is the cumulative measurement of vibration and increases as a function of the dose and magnitude of the vibration value.