Tools › Environmental › Health and Safety › Lifting and Heat Stress Limits › Example

Unloading a five-tier pallet onto a conveyor: Revised NIOSH Lifting Equation, multi-task Composite Lifting Index (Applications Manual Example 7)

ToolLifting and Heat Stress Limits
SourceWaters, T. R., Putz-Anderson, V., and Garg, A. (1994). Applications Manual for the Revised NIOSH Lifting Equation. DHHS (NIOSH) Publication No. 94-110, National Institute for Occupational Safety and Health, Cincinnati, OH. Example 7, Depalletizing Operation, pp. 84–90 and Figure 22.
LevelProfessional

Problem

A warehouse worker unloads 12 lb cartons (16 in cubes) from a pallet stacked five tiers high onto a conveyor 20 in above the floor, 12 cartons a minute (2.4 lifts per minute from each tier) for one hour followed by a 90-minute recovery period. There is no twisting and no control is needed at the conveyor. Find the recommended weight limit and lifting index of each tier and the Composite Lifting Index of the job.

Inputs to Enter

  • Five tasks, one per tier: load 12 lb; hands at the origin 4, 20, 36, 52 and 68 in above the floor; horizontal location 18 in for the bottom tier and 16 in for the others; destination height 20 in
  • Asymmetry angle 0°, 2.4 lifts/min per tier, fair coupling, no significant control at the destination
  • Lifting duration short (1 hour or less); multipliers rounded to two decimals as on the manual's worksheet; USCS (load constant 51 lb, inches)
Open the Lifting and Heat Stress Limits tool (loaded with this example)

Answers

  • Tier 1: HM 0.56, VM 0.81, DM 0.93, CM 0.95 → FIRWL 20.4 lb; FM 0.90 (interpolated between 2 and 3 lifts/min) → STRWL 18.4 lb (book 20.4 and 18.4)
  • FIRWL of tiers 2 to 5: 28.4, 28.7, 23.8, 19.9 lb; STRWL 25.5, 25.8, 21.4, 17.9 lb (book 25.6, 25.8, 21.4, 17.9; the worksheet multiplies the rounded FIRWL)
  • FILI 0.59, 0.42, 0.42, 0.51, 0.60 and STLI 0.65, 0.47, 0.46, 0.56, 0.67 (book 0.6, 0.4, 0.4, 0.5, 0.6 and 0.7, 0.5, 0.5, 0.6, 0.7); new task order tier 5, 1, 4, 2, 3 as in the book
  • Frequency multipliers at the cumulative frequencies 4.8, 7.2, 9.6 and 12 lifts/min: 0.81, 0.68, 0.48, 0.37; increments 0.072, 0.119, 0.259, 0.259 (book .07, .12, .26, .26)
  • Composite Lifting Index CLI = 0.670 + 0.072 + 0.119 + 0.259 + 0.259 = 1.38 (book 1.4): above 1.0 although every single task is below it; the lowest multiplier of every tier is the horizontal one

Notes

The tool's default inputs are this example; press Submit. The tool carries limits and indices unrounded where the worksheet rounds them to one decimal. All ten example problems of the manual and their redesigns are reproduced by test_lifting_heat_stress.php (411 checks), with an independent numpy implementation beside the library.