CIEE Environmental Factors & Human Performance 2 — Questions and Answers
Question 1: Which metric best quantifies the combined effect of air temperature, radiant heat, humidity, and air movement on worker heat stress?
- Wet Bulb Globe Temperature (WBGT) (Correct answer)
- Dry Bulb Temperature
- Effective Temperature Index
- Heat Stress Index (Belding-Hatch)
Correct answer: Wet Bulb Globe Temperature (WBGT)
WBGT integrates all four environmental heat factors and is the standard metric used by ACGIH and NIOSH for assessing occupational heat stress exposure limits.
Question 2: A worker performs repetitive assembly in a room where air temperature is 75°F but relative humidity is 90%. What is the primary ergonomic concern?
- Elevated perceived exertion and reduced heat dissipation through sweat evaporation (Correct answer)
- Increased static muscle load due to humidity effects on joint friction
- Enhanced cognitive performance due to moisture in the air
- Reduced glare from moisture on work surfaces
Correct answer: Elevated perceived exertion and reduced heat dissipation through sweat evaporation
High humidity impairs sweat evaporation, the primary heat-dissipation mechanism, raising core temperature and perceived exertion even at moderate air temperatures.
Question 3: Under NIOSH recommendations, which vibration frequency range poses the greatest risk of whole-body vibration (WBV) injury to the lumbar spine?
- 4–8 Hz (Correct answer)
- 20–40 Hz
- 60–80 Hz
- 100–200 Hz
Correct answer: 4–8 Hz
The lumbar spine resonates at 4–8 Hz, meaning whole-body vibration in this range is most efficiently transmitted to and absorbed by spinal structures.
Question 4: Which lighting parameter most directly affects a worker's ability to distinguish fine surface defects during visual inspection tasks?
- Luminance contrast (Correct answer)
- Color rendering index (CRI)
- Correlated color temperature (CCT)
- Illuminance uniformity ratio
Correct answer: Luminance contrast
Luminance contrast between a defect and its background is the primary determinant of visual detection performance for fine surface anomalies.
Question 5: A forklift operator complains of fatigue and lower back pain after 6-hour shifts. Which combination of environmental factors should be assessed first?
- Seat vibration frequency spectrum and seat suspension effectiveness (Correct answer)
- Ambient temperature and relative humidity in the warehouse
- Lighting levels at the operator's eye height
- CO2 concentration in the operator cab
Correct answer: Seat vibration frequency spectrum and seat suspension effectiveness
Forklift operators are a primary WBV risk population; characterizing vibration frequency and evaluating whether seat suspension mitigates the 4–8 Hz resonance range is the priority assessment.
Question 6: According to ACGIH, what is the recommended maximum ceiling illuminance (footcandles) for continuous VDT/computer workstations to prevent glare discomfort?
- 500 lux (≈50 fc) (Correct answer)
- 1000 lux (≈100 fc)
- 2000 lux (≈200 fc)
- 300 lux (≈30 fc)
Correct answer: 500 lux (≈50 fc)
ACGIH recommends ambient illuminance of approximately 300–500 lux (≈50 fc) for VDT tasks to balance screen visibility and prevent disability glare.
Question 7: Which personal protective approach is most effective for reducing hand-arm vibration (HAV) transmitted from a grinder to the operator?
- Anti-vibration gloves rated to ISO 10819 for the tool's dominant frequency (Correct answer)
- Standard leather work gloves
- Increasing grip force to stabilize the tool
- Widening tool handle diameter beyond 50 mm
Correct answer: Anti-vibration gloves rated to ISO 10819 for the tool's dominant frequency
ISO 10819-rated anti-vibration gloves are specifically tested at the tool's operating frequency range and provide documented vibration transmission reduction for HAV control.
CIEE Environmental Factors & Human Performance 2
Which metric best quantifies the combined effect of air temperature, radiant heat, humidity, and air movement on worker heat stress?