Human Factors and Ergonomics
What to master
Anthropometry and design limits (5th-percentile female for reach, 95th-percentile male for clearance), work physiology and manual material handling (NIOSH lifting equation, recommended weight limit, lifting index), biomechanics and cumulative trauma, and assessment tools such as RULA, REBA, and the Rodgers muscle-fatigue model. Cover cognitive topics - information processing, signal detection theory, vigilance, mental workload, and Fitts' law (MT = a + b x log2(2D/W)) - plus human-machine interface design: displays, controls, coding, feedback, and error-proofing. Environmental factors: illumination, noise (dBA, 85 dBA TWA action level, 3 dB exchange rate), vibration, and thermal stress (WBGT).
Traps
- Designing to the 50th percentile for something that must fit nearly everyone.
- Mixing reach (5th-percentile female) with clearance (95th-percentile male).
- Adding decibels arithmetically instead of logarithmically.
- Forgetting that NIOSH multipliers apply sequentially and each is capped at 1.0.
- Confusing noise dose with sound level; doubling identical sources adds about 3 dB.
- Treating Fitts' law slope and intercept as universal physical constants.
Worked example
Two machines each emit 80 dBA. Combined = 10 x log10(10^8 + 10^8) = 10 x log10(2 x 10^8) = 83 dBA. Ten identical sources add 10 dB - not ten times the level.
Rule of thumb
Design for the extremes, not the average: anything that must be reached should suit small users; anything that must be avoided (clearances, guard openings, door heights) should suit large users.