Elements of Ergonomics Programs A Primer Based on Workplace Evaluations of Musculoskeletal Disorders

The site was a large grocery warehouse with the focus on order selector jobs. Order selectors load cases of grocery items from warehouse shelves to pallets according to a "picking order" (a listing of the items and quantities to be picked), the order of picking the items, and their locations (aisle and slot numbers) in the warehouse. In terms of job tasks, the order selector routine is to drive a pallet jack to the location of the items in the warehouse, lift the items from the shelves, carry them to the pallet, and lift or lower the items onto the pallet and place labels on the items. The order selector then proceeds to the next item on the order list, and the procedure is repeated. After the entire list of orders is picked, the order selector wraps or tapes the stacked cases together and places the loaded pallet on the loading dock for transport from the warehouse. Order selection is known as a physically demanding job. One objective of the NIOSH evaluation was to assess the potential risk associated with the manual lifting tasks just described. Before the evaluation, a standard incentive program was installed at this warehouse to establish a "fair amount of time" for order selecting activities. Achieving 100% of the standard was considered a "day's work." Order selector performance was averaged over a week, and employees were disciplined for performance that fell below 95% of the standard. Workers who exceeded the standard were rewarded with additional pay or paid time off.

Techniques used to assess the potential risk associated with the manual lifting tasks performed by the order selectors included the following:

• Weight measurements of the objects lifted

• Videotape, still photos, and angular measurements of the body postures of workers carrying out the lifting tasks

• Use of a motion monitor to record the motion of the trunk as it may affect the forces on the intervertebral joints of the spinal column

• Time activity analysis of the manual lifting routines of the order selectors, including work-rest cycles

• Use of portable heart monitors and oxygen consumption meters to measure the energy expenditure in the course of carrying out regular order selector activities

The mean metabolic rates as measured by oxygen consumption were above the value (5.0 kcal/min) recommended in the literature as an upper limit for young male workers during an 8-hour workday. Observed heart rates were also high. Two of the three workers had average heart rates exceeding 110 beats/min, the suggested maximum acceptable for the majority of healthy workers [Astrand and Rodahl 1986].

Time-motion analyses of the data collected indicated that the average frequency of lifts during the normal activities of the selectors was 4.1 lifts/min. This lifting rate, coupled with observed loads averaging 30.4 lb, would probably result in fatigued muscles, especially since a high percentage (53%) of the lifts required extreme trunk flexion and reaches above shoulder height. Calculations for these lifting conditions were well above the upper limits recommended by the NIOSH lifting equation [Waters et al. 1993].

Data collected in this evaluation provided for workers' perceptions of the physical effort required by their jobs and the job demand versus the control they felt they had in their work routines. Findings here indicated "hard physical effort" as the average response, which correlated well with the heart rate and oxygen consumption monitoring already described. Responses to the job demand and control questions, when compared with other worker groups, showed order selecting to be a high demand and low control job. Informal interviews with workers revealed their concern over the work standards and their inability to control the pace of their jobs. The literature associates this combination of job attributes with increased stress and job dissatisfaction [HETA 91–405–2340].