CEA Workplace Assessment Methods 3 — Questions and Answers
Question 1: Which ergonomic assessment method uses a checklist of upper-limb posture, force, and repetition to generate a numeric risk score for each task?
- NIOSH lifting equation
- Occupational Repetitive Actions (OCRA) index (Correct answer)
- Psychophysical tables (Snook tables)
- Job Strain Model
Correct answer: Occupational Repetitive Actions (OCRA) index
The OCRA Index quantifies upper-limb disorder risk by scoring repetition, force, posture, additional factors, and recovery time across a work shift.
Question 2: An ergonomist using electromyography (EMG) during a workplace assessment is primarily measuring:
- Joint angle through the range of motion
- Electrical activity of muscles as an indicator of exertion level (Correct answer)
- Vibration magnitude transmitted to the hand-arm system
- Oxygen consumption as a proxy for workload
Correct answer: Electrical activity of muscles as an indicator of exertion level
Surface EMG electrodes detect electrical signals generated by muscle fibers, allowing the ergonomist to quantify muscle activation and relative effort.
Question 3: The Psychophysical approach to manual handling assessment, as developed by Snook and Ciriello, defines maximum acceptable weight based on:
- Biomechanical compression force limits at L4/L5
- Worker self-selected loads that are acceptable for a full shift without undue fatigue (Correct answer)
- NIOSH recommended weight limit calculations
- Cardiovascular strain measured by heart rate
Correct answer: Worker self-selected loads that are acceptable for a full shift without undue fatigue
The psychophysical method uses worker perception of effort to set the maximum weight or force that 75–90% of the population can perform across a full shift.
Question 4: During a lighting assessment for a visual display terminal (VDT) workstation, the ergonomist should prioritize measuring:
- Luminance ratio between the screen and surrounding surfaces (Correct answer)
- Color rendering index (CRI) of overhead fixtures only
- Illuminance level at the floor surface
- UV radiation from display panels
Correct answer: Luminance ratio between the screen and surrounding surfaces
Luminance ratios between the VDT screen and surrounding task and background areas directly affect visual fatigue and glare discomfort.
Question 5: Which component of the NIOSH Lifting Equation accounts for asymmetric trunk rotation during a lift?
- Horizontal Multiplier (HM)
- Vertical Multiplier (VM)
- Asymmetry Multiplier (AM) (Correct answer)
- Coupling Multiplier (CM)
Correct answer: Asymmetry Multiplier (AM)
The Asymmetry Multiplier (AM) penalizes lifts where the load is displaced from the worker's sagittal plane, reflecting increased spinal stress from trunk rotation.
Question 6: In a push/pull assessment using a force gauge, the ergonomist should capture both initial and sustained forces because:
- Initial force overcomes static friction and is typically higher than sustained force (Correct answer)
- Sustained force always exceeds initial force due to fatigue
- Both forces are equal and the choice is arbitrary
- Only sustained force predicts musculoskeletal disorder risk
Correct answer: Initial force overcomes static friction and is typically higher than sustained force
Initial force must overcome static friction to break the load from rest and is generally greater than the sustained force needed to keep it moving at constant speed.
Question 7: When assessing whole-body vibration (WBV) exposure, the primary measurement axis aligned with the spine of a seated worker is designated:
- X-axis (fore-aft)
- Y-axis (lateral)
- Z-axis (vertical) (Correct answer)
- W-axis (rotational)
Correct answer: Z-axis (vertical)
For seated workers, the z-axis runs vertically through the spine and is the principal axis for whole-body vibration assessment per ISO 2631-1.
CEA Workplace Assessment Methods 3
Which ergonomic assessment method uses a checklist of upper-limb posture, force, and repetition to generate a numeric risk score for each task?