CIEE Manual Material Handling Assessment 3 — Questions and Answers
Question 1: Which tissue is most commonly injured during repetitive manual material handling tasks involving awkward trunk flexion?
- Anterior cruciate ligament
- Intervertebral disc (Correct answer)
- Rotator cuff tendons
- Carpal tunnel median nerve
Correct answer: Intervertebral disc
Repeated trunk flexion combined with compression forces accelerates intervertebral disc degeneration, the most prevalent injury in manual handling workers.
Question 2: The Liberty Mutual Manual Materials Handling Tables define task acceptability in terms of the percentage of what population that can perform the task?
- Percentage of industrial workers over 50 years old
- Percentage of the male or female workforce capable of exerting the required force (Correct answer)
- Percentage of workers without prior back injury history
- Percentage of certified ergonomists who rate the task safe
Correct answer: Percentage of the male or female workforce capable of exerting the required force
The Snook and Ciriello (Liberty Mutual) tables express acceptable limits as percentages of male or female worker populations who can perform tasks without unacceptable strain.
Question 3: When evaluating a carrying task using the NIOSH approach, which condition makes carrying assessment significantly different from a standard lift assessment?
- Carrying always requires a higher load constant than lifting
- The horizontal and vertical distances change continuously throughout the carry (Correct answer)
- Carrying tasks must always be assessed bilaterally
- Frequency multiplier does not apply to carrying tasks
Correct answer: The horizontal and vertical distances change continuously throughout the carry
During carrying, the load position relative to the body changes with each step, making it difficult to identify a single set of NIOSH multipliers for the entire task.
Question 4: A worker carries 15 kg boxes a horizontal distance of 8 meters at a frequency of 4 lifts per minute over an 8-hour shift. Which risk factor is MOST concerning from an MMH perspective?
- The 15 kg box weight alone exceeds all NIOSH limits
- The combination of carrying distance and high frequency increases cumulative spinal loading (Correct answer)
- Carrying distances under 10 m are exempt from ergonomic assessment
- The 8-hour duration is the primary concern, not the carrying parameters
Correct answer: The combination of carrying distance and high frequency increases cumulative spinal loading
Long carry distances combined with high frequency dramatically increase cumulative metabolic and lumbar loading, even when individual load weight appears moderate.
Question 5: Which biomechanical model is most commonly used in ergonomic software (e.g., 3DSSPP) to quantify lumbar compressive forces during manual handling tasks?
- Two-dimensional static strength prediction model
- Three-dimensional static strength prediction (3D SSP) model (Correct answer)
- Psychophysical capacity model
- Metabolic energy expenditure model
Correct answer: Three-dimensional static strength prediction (3D SSP) model
3DSSPP uses a three-dimensional static strength prediction model to estimate joint reaction forces, including lumbar L4/L5 compression, for a given posture and external load.
Question 6: NIOSH recommends an action limit of 3.4 kN for lumbar compressive force. What percentage of working population is at elevated risk above this threshold?
- Less than 1% of workers
- Approximately 25% of workers (Correct answer)
- More than 75% of workers
- 100% of workers above age 45
Correct answer: Approximately 25% of workers
The NIOSH 3.4 kN action limit was set because approximately 25% of workers have insufficient disc strength to tolerate higher compressive forces safely.
Question 7: In the context of manual material handling, 'coupling' refers to:
- The transfer of force between two workers during a team lift
- The quality of the interface between the worker's hands and the load (Correct answer)
- The connection between the origin and destination of a lift
- The relationship between lift frequency and task duration
Correct answer: The quality of the interface between the worker's hands and the load
Coupling quality (good, fair, or poor) describes how well the worker can grasp and control the load, directly affecting the coupling multiplier (CM) in the NIOSH equation.
CIEE Manual Material Handling Assessment 3
Which tissue is most commonly injured during repetitive manual material handling tasks involving awkward trunk flexion?