Workshop Instructions: 1. Assess the manual lifting | Chegg.com - Free Printable

- (a) Measure and record task variables:
- Load weight (L): 10 kg
- Horizontal distance at start (H_start): 60 cm
- Vertical distance at start (V_start): 90 cm
- Vertical distance at end (V_end): 20 cm
- Vertical travel distance (D): |90 cm - 20 cm| = 70 cm
- Asymmetric angle at start (A_start): 45 degrees
- Asymmetric angle at end (A_end): 0 degrees (tray placed straight down)
- Frequency: 1 lift/minute
- Duration: 4 hours
- Coupling: “fair” grip
- Body posture: Feet fixed, upper body twist at START

- (b) Determine multipliers and compute RWL:
- Horizontal multiplier (HM) at start: HM_start = 25 / H_start = 25 / 60 ≈ 0.417
- Vertical multiplier (VM) at start: VM_start = 1 - 0.003 × |V_start - 75| = 1 - 0.003 × |90 - 75| = 1 - 0.045 = 0.955
- Distance multiplier (DM): DM = 0.82 + (4.17 / D) = 0.82 + (4.17 / 70) ≈ 0.82 + 0.0596 ≈ 0.8796
- Asymmetric multiplier (AM) at start: AM_start = 1 - (0.0032 × A_start) = 1 - (0.0032 × 45) = 1 - 0.144 = 0.856
- Frequency multiplier (FM): For 1 lift/min over 4 hours, FM ≈ 0.75 (from NIOSH table for duration > 2 hr, frequency 1/min)
- Coupling multiplier (CM): “Fair” grip → CM = 0.95
- RWL at start: RWL_start = 23 kg × HM_start × VM_start × DM × AM_start × FM × CM
RWL_start = 23 × 0.417 × 0.955 × 0.8796 × 0.856 × 0.75 × 0.95 ≈ 23 × 0.215 ≈ 4.95 kg
- Note: Since the task involves a significant asymmetric component only at start and ends symmetrically, RWL is typically calculated for the most stressful point (start). If required for end, AM_end=1, but load is placed, so lifting force is minimal.

- (c) Compute the lifting index (LI):
- LI = Load Weight / RWL_start = 10 kg / 4.95 kg ≈ 2.02

- (d) Make your conclusion(s) based on the results:
- The Lifting Index (LI) of approximately 2.02 indicates that the task is more than twice as stressful as the recommended limit. This suggests a significantly increased risk of lower back injury.
- Key contributing factors include the large horizontal distance (60 cm), the asymmetric twisting motion (45°), and the fair grip.
- Recommendations: Reduce horizontal reach by repositioning the conveyor or cart; eliminate twisting by aligning the tray path with the worker’s sagittal plane; improve grip by using trays with better handles; consider mechanical aids or team lifting.
- The task should be redesigned to reduce risk, as it exceeds safe limits according to NIOSH guidelines.