Ergonomics and Human Factors Engineering
Ergonomics and Human Factors Engineering
The exam tests whether you can quantify physical exposures, recognize WMSD risk factors, and design work for human capability rather than average assumptions.
Core rules
- WMSD risk factors include forceful exertion, repetition, awkward posture, vibration, contact stress, and insufficient recovery time. They interact; one factor alone is rarely the whole story.
- The NIOSH lifting equation calculates a recommended weight limit: RWL = LC x HM x VM x DM x AM x FM x CM, with load constant LC = 23 kg. The lifting index (LI) is load divided by RWL; LI above 3 is high risk, and above 1 exceeds the recommended limit for most workers.
- Observational tools such as RULA and REBA screen postures but do not replace exposure measurement.
- Anthropometry and reach envelopes should be applied with population percentiles; designing for the 50th percentile fits almost nobody well.
- Human factors includes error-likely conditions: unclear displays, similar-looking controls, time pressure, and poor feedback. Design should make the correct action easy.
Worked example
A worker lifts a 15 kg box from floor level (V = 50 cm), 50 cm in front (H = 50 cm), through 50 cm (D = 50 cm), with no asymmetry (A = 0) and a fair coupling (CM = 0.95). HM = 25/50 = 0.50. VM = 1 - 0.003|50 - 75| = 0.925. DM = 0.82 + 4.5/50 = 0.91. AM = 1.0. FM for 1 lift/minute is about 0.88. RWL = 23 x 0.50 x 0.925 x 0.91 x 1.0 x 0.88 x 0.95, approximately 8.1 kg. With a 15 kg load, LI is about 1.85, so the task exceeds the recommended limit and needs engineering redesign, not just lifting technique training.
Traps
- Comparing the load to 23 kg and ignoring geometry and frequency.
- Treating training as a control for a lifting index above 1.
- Using RULA scores as injury diagnoses.