MECHANICAL LOADING ON THE LOW-BACK IN 3 METHODS OF REFUSE COLLECTING

The mechanical loading on the low back was studied in three different current methods of refuse collecting: in polythene bags, two-wheeled m ini-containers and large four-wheeled containers. To this end the most prominent activities of each collecting method were performed in a la boratory. On the basis of movement analysis, force measurements and bi omechanical modelling, spinal compressive and shear forces were estima ted. From these forces and from the frequency of activities during the working day (assessed in a preliminary held study) the low-back stres s in each collecting method was evaluated. In the bag-method, peak for ces when throwing the bags ranged from 3341 to 5179 N (average compres sion) and from 284 to 673 N (shear) among the different conditions stu died. The act of picking up bags also showed rather high forces (excee ding the NIOSH limit for disc compression in most cases). The frequenc y of exposure to these forces in the field is rather high (workers pic k up and throw on average 807 times each day). The mini-container meth od compares favourably to the bags method. Peak compressive and shear force in tilting/pushing and pulling mini-containers ranged from 1657 to 2654 N and from 123 to 248 N respectively. Also, the frequency of s tressful events in the field is lower in this method. In the large con tainer method extremely high peak forces (e.g. compression ranged from 4991 to 5810 N) were observed in the task of putting the empty contai ner back from street level to sidewalk level (surmounting the kerb). T he frequency of activities like pushing, pulling and lifting the large container in the field is much lower compared with activities in the other methods. On the basis of the frequency and magnitude of spinal f orces it was concluded that the mini-containers should be preferred to the bags. If kerbs are removed at container places and tasks are perf ormed by two instead of a single person, the large container method wo uld form another good alternative to the stressful task of collecting refuse in bags.