Whole-body Vibration (WBV) concerns the transfer of relatively low frequency environmental vibration to the human body through a broad contact area. These frequencies are in the range of 0.5 to 80 Hz (ISO, 1). Transmission occurs through the feet when standing, the buttocks when sitting (most common scenario), or the entire body length when reclining in contact with the vibrating surface. WBV exposures exist in many occupational settings.
The body as a whole and individual organs have natural frequencies that can resonate when receiving vibration energy at the natural frequency. Resonance of the body or its parts due to WBV is suspected to cause adverse health effects, primarily with chronic exposure. Presently, most of the evidence supporting this relationship is epidemiological. Direct medical evidence is scarce, especially when compared to the greater amounts of data available for hand-arm vibration (HAV) illnesses that occur at higher frequency ranges. HAV exposures occur with higher vibration frequencies applied to the fingers and hands using powered hand tools, resulting in known adverse health effects such as "white finger" (Janicak, 35).
Standards are available for reference in the US. However, there are no specific regulations mandating identification, monitoring and control of WBV, such as within OSHA standards (OSHA). In Europe, WBV monitoring and exposure limits have been addressed in mandatory standards and directives.
WBV monitoring is somewhat similar to the methodology used for occupational noise. Accelerometers are used in placed of a microphone and recording the direction of vibration waves is critical. WBV is measured as oscillation about a fixed point in m/s2 A survey of US safety and health professionals was conducted in May 2006 to determine knowledge and awareness of WBV. Analysis of the data revealed a relatively low knowledge of the topic. Of those responding to the survey, 69.5% self-reported less than a basic understanding of WBV (Paschold, 56).
Many positive steps can be undertaken to eliminate or reduce harmful WBV exposure. These methods can include engineering re-design, procedural changes, or employee training. However, before these corrective actions can be undertaken, identification and assessment of WBV exposure is needed.
WBV is caused by the transmission of environmental vibration waves to the human body. A wave in its simplest form is depicted in Figure 1. Frequency is characterized by wavelength and displacement (power) by amplitude. In reality, we not normally exposed to a vibration of a pure simple single wave; exposures are to a multitude of simultaneous waves of differing frequency, magnitude and direction.(Figure in full paper)
The transmission of WBV to the human body at the natural frequency of the body as a whole or its parts will result in resonance. and noise energy, rapid variations in air pressure, is measured and recorded in decibels. Measurement of WBV entails the collection of much more data than with noise monitoring, increasing the requirements for sophistication of instruments and methods of data logging.