As the harmful effects of vibration increase with the magnitude of vibration and the duration of exposure, workers’ vibration exposure is determined on the basis of the level of vibration to which they are exposed during each period of exposure and the length of each period of exposure. The figures are used to calculate each worker’s daily vibration exposure, which is then compared against the vibration exposure action values and limit values. The assessment must give the employer reliable information on whether the action values or limit values are exceeded.

A worker’s daily vibration exposure factors in all vibrating surfaces that they handle during a typical working day. The vibration magnitude during these contacts with vibrating surfaces as well as the duration of each contact are estimated or measured to calculate exposure during each period of contact. A worker’s daily vibration exposure (A(8)) is calculated by adding up the exposures from all periods of contact with vibrating surfaces during their working day and then dividing the figure across eight hours. Exposure to hand-arm vibration and whole-body vibration are calculated separately.

Determination of vibration magnitude

The magnitude of vibration is measured from the point of the surface where the vibration is transmitted to a worker’s hands or body, i.e. the point between a handle and a worker’s hand, between a seated worker and the seat, or between the soles of a standing worker’s feet and the floor. In the case of hand-held tools and heavy machinery, the magnitude of vibration can be estimated on the basis of the vibration emission figures provided in the manufacturer’s instructions. Many research organisations have also compiled data on the vibration levels of different kinds of machinery. Certain multiplicative factors need to be applied if the magnitude of vibration is estimated on the basis of such data in order to get a better idea of the actual level of exposure.

Provisional estimates of vibration exposure can be based on information provided by the manufacturer or other available data. If no such information is available or if a worker’s exposure is believed to be close to the action value or the limit value, the exact magnitude of the vibration must be measured in the workplace. A reliable vibration exposure assessment usually requires hiring a professional with proper measuring equipment.

Determination of the duration of vibration exposure

Only the period of time during which a worker is actually exposed to vibration, i.e. the length of time during which vibration is transmitted to the worker’s hands or body from a vibrating surface, should be taken into account. The period of exposure is therefore based on the period of time during which a worker is holding a vibrating hand-held tool, sitting on a vibrating seat or standing or lying on a vibrating surface.

Calculation of daily vibration exposure

A worker’s daily vibration exposure can be calculated once all the periods during which the worker is exposed to vibration during their working day, the magnitude of vibration during each period of exposure and the length of each such period are known. There are several different methods available, with vibration counters being the simplest.

The Finnish occupational safety and health administration’s vibration counter can be used to calculate the daily exposure of workers who are exposed to vibration on up to seven different occasions during their working day.

Vibration counter (Excel, in Finnish, 38 KB)

Manufacturers’ responsibilities

Manufacturers have a duty to include information about the magnitude of hand-arm vibration caused by their hand-held or manually operated tools in the operating instructions. The operating instructions for heavy machinery must also include information about both hand-arm and whole-body vibration.