Analyse van de blootstelling aan trillingen tijdens werk in de groenvoorzieningen

Analysis of the exposure to whole-body and hand-arm vibrations during work in the green area

Huub H.E. Oude Vrielink

 

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Summary

European and Dutch legislation define maximum values, i.e. action values and limit values, for whole-body vibration (WBV) and hand-arm vibration (HAV) to which employees may be exposed on a working day. A transition period is defined until July 2014 for agriculture and forestry. The legislation is meant to protect the workers from health damage due to exposure to vibrations. If the action value (0.5 and 2.5 m/s2 for WBV and HAV, respectively) is exceeded, organisational and/or technical measures are to be taken and health surveillance is to be organised, in order to limit or reduce the exposure. In case of exceeding the limit value (1.15 and 5 m/s2, for WBV and HAV), exposure should be brought back immediately to below this limit value. The maintenance of the green area, using mowing machines, hedge trimmers, leaf blowers, brush cutters or clearing saws is considered to be a set of working activities that need advice on how exposure to vibrations can be reduced. The present research aimed to make an estimation of the daily exposure to WBV and HAV when using modern green area machinery for the activities mentioned above during a normal working day action. In addition, it was investigated to which extent exposure can be influenced actively by the user and the management by comparing different brands of the equipment.

Exposure measurements were performed with a total of 8 experienced professional workers on five different tasks (mowing of sports fields, mowing of city green area, hedge trimming, leaf blowing, and cutting of long grass aside the road), organised such that each piece of equipment was tested by two workers during normal work in practice and each task consisted of a minimum of two machines. Vibration evaluation was performed according to ISO (2631-1, 1997, 2631-5, 2001 and 5349-1, 2001) on the seat (WBV) and at the steering wheel (HAV) for mowing machines, and at the handle or handles (HAV) for all hand-held equipment. Besides, vibrations of the chassis at the chair base were measured for the mowing machines, to determine the effectivity of damping (SEAT-value) of the chair implemented. Vibrations for each measurement site were sampled and evaluated in the 3 standard directions X (for-afterward), Y (sideward), and Z (vertical) for WBV (aw) and as vector sum ahv for HAV. During the tests, vibration results were displayed on-line digitally on a laptop computer and were stored. Processing of the data and calculation of outcome variables were performed off-line. The effect of two different cutting utilities (head containing flexible cord, or metal blade) was measured separately when testing the brush cutters. The effect of two different kinds of pipe endings (straight or curved) was tested for one of the leaf blowers. For the interpretation of the vibration values measured into daily exposure values, normal working patterns were obtained by interview of the Netherlands organisation for employers in the green area (vhg).

For mowing of sports fields, whole body vibration values ranged between 0.41 and 0.50 m/s2, the vertical vibration being highest. The differences between both persons and machines were small. Mowing of city green area resulted in whole body vibration values of 0.61, 0.61 and 0.47 m/s2 (median, for X-, Y-, and Z-direction, respectively). These data are based on a working pattern of 10% of the working time driving on paved city roads (in our case: merely asphalt) and 80% of the time actually mowing. The action value for horizontal vibrations is exceeded after 4.6 tot 5.8 (median: 5.4) hours of work.

The trimming of hedges resulted into median vibration values ahv of 4.47 m/s2 and 3.27 m/s2 for the front and rear handle, respectively. These data are based on a working pattern of 20% of the working time holding the machine running stationary and 60% of the time actually trimming. The action value was exceeded after 4.0 hours when operating the machine with the lowest vibration exposure.

During the measurements of the blowing of leaf, a large difference between both machines tested was found: ahv = 1.4 – 5.0 m/s2 and 1.8 – 3.6 m/s2 for operating the machine running stationary and while blowing leaf, respectively (data are median values for two subjects). These values resulted into a spread in daily vibration exposure between both machines of 1.8 to 3.7 m/s2, assuming a daily working pattern of 10% of the working time holding the machine running stationary and 80% of the time actually blowing leaf. Using the one machine did not result in exceeding the action value, while using the other this happened after 3.6 hours. No difference in exposure was found between straight and curved pipe ending usage.

 

During the use of brush cutters, higher vibration exposure values were found for all machines for the left hand (median ahv = 4.50 m/s2) compared to the right (median ahv = 4.11 m/s2). These data are based on a daily working pattern of 20% of the working time exposed to the machine running stationary and 60% of the time actually cutting the grass. When operating the lowest vibration emission machine, the action value was exceeded after 3.2 hours. No difference in exposure was found between both cutting utilities.

The following conclusions can be drawn; (1) During mowing of city green area, attention must be paid to reduction of whole body vibration in the horizontal plane. It is speculated that a more smooth driving behaviour and/or the mounting of a chair, containing damping mechanisms for vibrations in the for-afterward and sideward directions, in addition to the vertical axis, will reduce whole body vibration exposure. This has to be confirmed with additional measurements. (2) Exposure to hand-arm vibrations during trimming of hedges, blowing of leaf and handling of brush cutters appears too high: the action value is exceeded after maximally 3 to 4 hours of work, assuming daily working patterns obtained by interview. This was true for all machines except one: one machine for blowing of leaf could be handled for a full working day without exceeding the European norm. For the other working activities investigated, it is advised, in order to reduce exposure, to limit the working time per day and to reduce the handle grip time while the machine is running stationary.


    

Source: www.ergolabresearch.eu.