Rating of acceptable loads in manual sorting of postal parcels

The psychophysical test, the rating of acceptable load (RAL) were used to assess acceptable weights for dynamic lifting in postal workers engaged in sorting parcels. The standard test (RAL_St) and a work-simulating test (RAL_W) were administered to 103 volunteers: all experienced male sorters. In the RAL_St, subjects selected the weight which would be acceptable for lifting in a box with handles from table to floor and back to the table once every 5 min for the working day. For the RAL_w, the box was without handles and the weight was chosen to be acceptable for transfer 4-6 times/min from a table to the parcel container and back to the table. Both tests were made during normal working hours at postal sorting centres. The overall means for RAL_St and RAL_w were 16·4 kg and 9·4 kg respectively (p < 0·001): both being substantially higher than the average parcel weight of 4 kg. The RAL_St and RAL_w tests proved to be repetitive and sensitive for differentiating the effects of load and task variables in actual manual materials handling. Thus they appear to be applicable to the evaluation of manual materials handling problems.