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Ergonomic Job Analyses Of Picking Tasks In A Wholesale Grocery Warehouse Distribution Center.

by Nancy E. Laurie M.S., Robert O. Andres Ph.D., CPE, David D. Wood M.S.I.E.

Abstract

In 1993 a job analysis for a wholesale grocery warehouse distribution company was performed. OSHA 200 logs suggested approximately 30% of the recordable cases were back related with selectors experiencing the greatest number of back injuries. Quantitative job analyses of 4 different order selector jobs were performed. The jobs were analyzed using a three dimensional analysis of static strength requirements and an analysis of repetitive lifting using the NIOSH Lifting Equation. Results indicated that tasks involving lifting cases above 50 lb and/or requiring the worker to reach horizontally beyond 20" to handle a case created high stress in the low back and/or shoulder. Meat selectors appeared to be exposed to the highest physical stresses, followed by the freezer and grocery selectors. Recommendations included: decreasing case weights to 50 lb or less; decreasing the horizontal reach distance by having a designated puller move cases to the front of the slot; and rotating workers to decrease repetitive movements.

Introduction

In 1993 we had the opportunity to set up an Ergonomics Program for a large wholesale grocery warehouse distribution company. The operation consisted of 3 warehouses with 1,500 employees working 3 shifts, 7 days a week, all year round. The company's operations were based on an incentive pay system and worker chosen teams. Therefore, the fastest workers were allowed to team up in order to select more items and hence, make more money. As an early component of Ergonomic Program implementation, biomechanical job analyses were performed. Initially, OSHA 200 logs and accident reports were investigated to determine which jobs contributed most to injuries and which injuries were most prevalent. The injury and illness experience at the distribution center prior to initiation of an Ergonomics Program is presented graphically in Figures 1-3. The percentage of OSHA recordable cases that were back cases versus cumulative trauma disorder (CTD) cases was consistent from 1990-1993 (see Figure 1). The increase in the number of injuries from 1991 to 1992 reflects an increase in the number of selectors. Approximately 30% of the recordable cases were back related, whereas less than 10% of the cases were CTDs. To determine where the majority of the ergonomic related disorders were occurring, back injuries were tabulated by department and by jobs within departments (Figures 2 & 3). Selectors experienced the greatest number of back injuries by far, followed by the forklift operators. The grocery department had almost twice as many injuries as the freezer department, followed by meat and dairy in third place. Strains outnumbered all other types of injury, followed by contusions and then sprains. Most of the injuries involved the back, with the foot being injured about half as often. Since selectors had the highest number of back injuries, quantitative job analyses of the four different selector jobs were performed and will be the focus of this paper.

Figure 1: The types of injuries and illnesses as a percentage of the total recordable cases for 1990-1993.

Figure 2: Injuries by department for the first 6 months of 1994.

Figure 3: The number of back injuries by job type from 1990-1993.

Methods

Four job categories were analyzed with biomechanical techniques including a three dimensional analysis of static strength requirements and an analysis of repetitive lifting using the revised National Institute for Occupational Safety and Health (NIOSH) Lifting Equation. The job categories included: meat, dairy, grocery and freezer selectors. Approximately 10 minutes of video of workers performing each job were gathered. Frequency data were estimated from the "Team Statistic Reports" for each job for January, 1994. Measurements of horizontal and vertical locations of the loads being handled were taken with a measuring tape and loads being handled were weighed. Some data were estimated by plant personnel familiar with the operations. We were informed that these workers occasionally worked overtime. The revised NIOSH Lifting Equation does not address overtime work, but we can assume that the effect of the longer work period would reduce the maximum acceptable weight by some amount (which would have to be determined by further study).

The data collected were analyzed using the Three Dimensional Static Strength Prediction Program (3DSSPP from the Center for Ergonomics, The University of Michigan) and the Lifting Advisorª (Revised NIOSH Lifting Equation (Waters et al., 1993) implemented by Ergonomic Engineering, Inc.) to account for the effects of isolated lifts and repetitive lifting, respectively. Results are presented separately for each of the jobs examined.

Results

Table 1 contains the data used for the Lifting Advisorª analysis of meat selectors. Several combinations of horizontal and vertical distances were used. Table 2 contains the results at the origin and destination positions of the lift.

Table 1. Lifting Advisorª data for meat selectors.

Table 2. Lifting Advisorª results for meat selectors (at the origin and destination). All distances are in inches and recommended weight limits (RWLs) in pounds.

A three dimensional back compression analysis (using 3DSSPP) was performed on lifting a large package of beef. We selected weights of 75 pounds to represent the current size, and 50 pounds to see the effect of reducing the weight. Three anthropometries were selected to cover an entire range of body types (5th, 50th, and 95th percentile males). Low back compression was checked at the origin and destination of a lift. The origin was the far end at the lowest level of a pallet and the destination was the far end of a nearly full pallet (shoulder height lift). Tables 3 contains the results for the origin and destination of the lift.

Table 3. 3D back compression at the origin (low/far) and destination (high/far) of the lift.

The dairy selector's job appeared to be less stressful than the meat selectors. The frequency was higher (3 lifts per minute versus 2 lifts per minute for the meat selectors) but the weights were lower. Two or three small cases weighing 4 to 10 pounds were stacked and lifted together. The total weight lifted was often around 20 pounds. The company's computer generated a "shot" (part or all of an order which will fill a pallet). The shot and dairy cold room are designed so that the heavy items (juice and butter) are selected first and essentially dropped onto the pallet.

Table 4 contains the data for the Lifting Advisorª analysis for the grocery selectors. Several combinations of horizontal and vertical distances were used. Table 5 presents the results.

Table 4. Lifting Advisorª data for grocery selectors.

Table 5. Lifting Advisorª results for grocery selectors (at the origin and destination).

Although the freezer selectors performed their job at a slower rate than the grocery selectors (3 per minute versus 4 per minute for the grocery selectors), the extremely low temperature in the freezer (-20 F) may increase the risk level of the freezer selectors to that of the grocery selectors. It is hypothesized that the cold will cause an earlier onset of whole body fatigue due to the calories burned to maintain body heat and localized fatigue due to the increase in grip force that workers exert when deprived of sensory feedback.

Conclusions

Both types of analyses indicate that certain tasks, particularly those involving lifting cases above 50 lb. and/or requiring the worker to reach horizontally beyond 20" to handle a case, create high stress on the body. This stress is usually greatest in the low back or shoulder region. Meat selectors appear to be exposed to the highest physical stress, followed by the freezer and grocery selectors. Dairy selectors experience less biomechanical stress than the others.

Based on our analyses, there are three major risk factors that need to be addre