CIH Ergonomics and Biomechanics 5 — Questions and Answers
Question 1: Which biomechanical principle explains why a longer moment arm increases the compressive force on the lumbar spine?
- Newton's third law of equal and opposite reactions
- Torque = Force × Distance, requiring greater counterbalancing muscle force (Correct answer)
- Bernoulli's principle of fluid dynamics in disc material
- Pascal's law of pressure transmission in synovial fluid
Correct answer: Torque = Force × Distance, requiring greater counterbalancing muscle force
A longer moment arm (farther load from the spine) increases torque, requiring greater erector spinae force and compressive disc loading.
Question 2: Under OSHA's General Duty Clause, an employer's failure to address a recognized ergonomic hazard may result in a citation when:
- A specific OSHA ergonomics standard exists for that industry
- Workers' compensation claims exceed $10,000 annually
- A feasible means of abatement exists and the hazard causes or is likely to cause serious harm (Correct answer)
- More than 10 percent of the workforce files MSD complaints
Correct answer: A feasible means of abatement exists and the hazard causes or is likely to cause serious harm
The General Duty Clause applies when a recognized hazard is likely to cause serious harm and feasible controls are available, even without a specific standard.
Question 3: When evaluating hand-arm vibration (HAV) exposure, which health outcome is the occupational hygienist most concerned about?
- Carpal tunnel syndrome from static median nerve compression
- Vibration-induced white finger (Raynaud's phenomenon) (Correct answer)
- Thoracic outlet syndrome from elevated shoulder posture
- Epicondylitis from repeated wrist flexion-extension
Correct answer: Vibration-induced white finger (Raynaud's phenomenon)
Vibration-induced white finger (VWF) is the hallmark vascular disorder caused by chronic hand-arm vibration from power tools.
Question 4: In designing a packing station, a CIH recommends using a 'lift table' that adjusts between 30 and 48 inches. This is an example of:
- Administrative control through job rotation schedules
- Engineering control via workstation adjustability (Correct answer)
- PPE substitution reducing direct exposure
- Work practice control modifying worker behavior
Correct answer: Engineering control via workstation adjustability
Adjustable equipment that physically changes the work environment to fit the worker is an engineering control.
Question 5: The 'Composite Lifting Index' (CLI) in the revised NIOSH lifting equation is used when:
- A single homogeneous lifting task is performed all shift
- Multiple different lifting tasks are performed during a shift (Correct answer)
- Two workers perform a team lift simultaneously
- Push and pull forces are combined with vertical lifts
Correct answer: Multiple different lifting tasks are performed during a shift
The CLI combines individual lifting indexes from multiple tasks to assess overall MSD risk when workers perform varied lifting throughout a shift.
Question 6: A production supervisor claims that adding wrist splints for all assembly workers is the optimal ergonomic solution. A CIH should respond that:
- Wrist splints are the preferred intervention and should be issued immediately to all workers
- PPE such as splints should only be used after engineering and administrative controls have been evaluated (Correct answer)
- Splints are contraindicated for assembly work and should never be used
- Splints must be validated with an EMG study before implementation
Correct answer: PPE such as splints should only be used after engineering and administrative controls have been evaluated
Per the hierarchy of controls, PPE is the least preferred option and should supplement, not replace, engineering and administrative controls.
Question 7: Which measure best quantifies the cumulative trauma risk from repetitive hand-intensive work per the ACGIH TLV for hand activity?
- Peak force alone normalized to MVC
- Hand Activity Level (HAL) combined with normalized peak force (Correct answer)
- Duty cycle percentage during the full work shift
- Wrist deviation angle measured by electrogoniometer
Correct answer: Hand Activity Level (HAL) combined with normalized peak force
The ACGIH TLV for hand activity plots HAL (repetition rate and duty cycle) against normalized peak force to define action limits.
CIH Ergonomics and Biomechanics 5
Which biomechanical principle explains why a longer moment arm increases the compressive force on the lumbar spine?