PU635 Unit 7 Ergonomic Assessment Example

Lifting Index 4.69 at the Hopper Rim: A Unit 7 Ergonomic Assessment Running One Fifty-Pound Sack Lift at a Composite Bakery Through the Revised NIOSH Equation, Then Redesigning It Twice

[Student Name]

Purdue University Global

PU635: Survey of Environmental and Occupational Health

Unit 7 Ergonomic Assessment

[Instructor Name]

[Date]

Corliss Street Bakery, its measurements and its workers are composite; the lifting equation, its multipliers and the research cited are real.

The Task

Two ingredient room workers share the job across the morning. A pallet of rye sacks sits on the floor beside the mixer. The worker bends, grips the sack, lifts it to the hopper rim at 44 inches, turns to the right to reach the opening, slits it and tips it in. Eight sacks go in during each twenty-minute mixing cycle, and the task runs for most of a seven-hour working period, with a half-hour break. The sacks are multiwall paper, without handles, and they sag in the middle when lifted. Six of the nine strains on the plant's OSHA 300 log over two years came from this room and the mixing area next to it.

Measurements

Taken with a tape and a protractor on the Tuesday morning shift, at the origin and the destination of the lift.

1. Load: 50 pounds.

2. Horizontal distance, hands to the midpoint between the ankles: 18 inches at the origin, 22 at the destination, where the worker reaches over the rim.

3. Vertical height of the hands: 10 inches at the pallet, 44 at the rim.

4. Vertical travel: 34 inches.

5. Asymmetry: 0 degrees at the origin, 60 degrees at the destination, because the hopper opening sits to the worker's right.

6. Frequency: 8 lifts in 20 minutes, 0.4 a minute, taken at the 0.5 row of the frequency table.

7. Duration: long, more than two hours.

8. Coupling: poor, because the equation's coupling definitions class non-rigid bags that sag in the middle as poor grips, whatever the worker's skill (Waters et al., 1994).

The Equation at the Origin

The recommended weight limit is the load constant of 51 pounds multiplied by six factors (Waters et al., 1993).

1. Horizontal multiplier: 10 divided by 18, 0.556.

2. Vertical multiplier: 1 minus 0.0075 times the distance from 30 inches, here 20, giving 0.850.

3. Distance multiplier: 0.82 plus 1.8 divided by 34, giving 0.873.

4. Asymmetric multiplier: 1.000.

5. Frequency multiplier, long duration, 0.5 a minute: 0.81.

6. Coupling multiplier, poor: 0.90.

Recommended weight limit: 51 times all six, 15.3 pounds. Lifting index: 50 divided by 15.3, 3.26.

The Equation at the Destination

1. Horizontal: 10 divided by 22, 0.455.

2. Vertical: 14 inches from 30, giving 0.895.

3. Distance: 0.873.

4. Asymmetric: 1 minus 0.0032 times 60, giving 0.808.

5. Frequency: 0.81.

6. Coupling: 0.90.

Recommended weight limit: 10.7 pounds. Lifting index: 4.69. The worse end of the lift is the top, not the floor, because the reach over the rim and the twist to the right cost more than the bend.

Reading the Multipliers as Causes

Each multiplier below 1.0 is a cause of the problem, and the size of each shows where redesign pays. At the destination, the horizontal reach of 22 inches costs more than half the load constant on its own. The 60-degree turn removes a further fifth. The low pallet costs 15 percent at the origin. Frequency and coupling are smaller penalties, and the load itself, 50 pounds against a constant of 51, leaves no margin for any of them. A lifting index above 3.0 indicates a task that many workers would be at elevated risk performing, so neither end is acceptable as it stands.

Redesign One: Raise the Origin, Move the Destination

A spring-loaded pallet lift table keeps the top of the stack at 30 inches as sacks are removed. The Unit 4 bag-dump station sits directly in front of the worker, with a 36-inch sill, and its grate brings the sack's center to 14 inches from the body. Origin: horizontal 12 inches, 0.833; vertical 30, 1.000; travel 6 inches, distance multiplier 1.000; asymmetry 0; frequency 0.81; coupling 0.90. Recommended weight limit 31.0 pounds; lifting index 1.61. Destination: horizontal 14 inches, 0.714; vertical 36, 0.955; distance 1.000; asymmetry 0; frequency 0.81; coupling 0.90. Recommended weight limit 25.4 pounds; lifting index 1.97. The redesign removes the twist and most of the reach and more than halves the index, but a 50-pound sack is still too heavy for this frequency and grip.

Redesign Two: Half-Weight Sacks

The rye supplier offers 25-pound sacks at a small premium. Sixteen sacks per cycle double the frequency to 0.8 a minute, taken at the 1.0 row, with a long-duration multiplier of 0.75. The lighter sack is held closer, so the horizontal distance at the station drops to 12 inches. Origin: 31.0 pounds recalculated with the new frequency multiplier gives 28.7 pounds; lifting index 25 divided by 28.7, 0.87. Destination: horizontal 0.833, vertical 0.955, distance 1.000, asymmetry 1.000, frequency 0.75, coupling 0.90; recommended weight limit 27.4 pounds; lifting index 0.91. Both ends are now below 1.0. The doubled frequency costs some of the gain, and the assessment shows that cost rather than hiding it.

Symptom Survey and Injury Log

All eight mixing-room workers answered a short body-map questionnaire. Five reported low back pain in the past year, three of them pain that kept them from normal activity at least one day, and four reported right shoulder pain, which fits the twist toward the hopper. The 300 log records six strains in two years for this group, two with restricted duty. The survey is small and self-reported. It agrees with the equation about where the problem is.

Limits of the Equation

The equation assumes two-handed, smooth lifting in a stable posture, and it does not model the tipping motion at the end of the lift, the slit-and-pour with arms extended, which is likely to load the shoulders beyond what the index captures. It also covers only lifting, not the pushing of dough troughs elsewhere in the room. The lifting index is a screening tool, not a prediction for any one worker. In a cross-sectional study of 50 lifting jobs, the odds of low back pain rose as the index climbed from 1.0 to 3.0, peaking at an odds ratio of 2.45 between 2 and 3, while jobs above 3.0 showed a lower odds ratio of 1.45 (Waters et al., 1999). That supports using the index to rank tasks and test redesigns, as this assessment does, rather than to predict who will be hurt.

Recommendation

Install the lift table and the dump station together, which the Unit 4 plan already schedules for month two, and switch rye to 25-pound sacks. Recalculate after installation using measured rather than planned distances.

References

Waters, T. R., Baron, S. L., Piacitelli, L. A., Putz-Anderson, V., Skov, T., Haring-Sweeney, M., Wall, D. K., & Fine, L. J. (1999). Evaluation of the revised NIOSH lifting equation: A cross-sectional epidemiologic study. Spine, 24(4), 386-394. https://doi.org/10.1097/00007632-199902150-00019

Waters, T. R., Putz-Anderson, V., & Garg, A. (1994). Applications manual for the revised NIOSH lifting equation (DHHS [NIOSH] Publication No. 94-110). National Institute for Occupational Safety and Health.

Waters, T. R., Putz-Anderson, V., Garg, A., & Fine, L. J. (1993). Revised NIOSH equation for the design and evaluation of manual lifting tasks. Ergonomics, 36(7), 749-776. https://doi.org/10.1080/00140139308967940