Ergonomics & Human Factors

Designing work to fit people. Learn physical ergonomics (anthropometry and percentiles, posture, manual material handling, the revised NIOSH lifting equation, RULA/REBA), work physiology and fatigue, workplace environment (lighting, noise, heat), cognitive ergonomics (displays, controls, mental workload, human error), organisational ergonomics and safety — with Python applying the NIOSH lifting equation.

Musculoskeletal disorders (back pain, carpal tunnel, shoulder injuries) are among the most common causes of lost work time. Poorly designed displays and procedures cause human errors in control rooms, cockpits and hospitals. Ergonomics — or human factors — designs tasks, tools and environments around human capabilities and limits.

Good ergonomics is good business: fewer injuries, less fatigue, fewer errors and higher productivity.

An analogy

Ergonomics is tailoring instead of forcing: rather than making every worker squeeze into one standard 'suit' (workstation), you design adjustable workstations that fit the range of bodies that will actually use them.

Anthropometry and workstation design

Body dimensions vary widely; design for ranges, not averages. Clearance dimensions (door height, knee room) use the large person (95th percentile); reach dimensions (shelf height, control location) use the small person (5th percentile); adjustable features cover 5th–95th. Work-surface height depends on the task: precision work higher, heavy work lower than elbow height.

Manual handling and posture

Assessment tools:

Environment

Lighting: 300–500 lux for offices, 750–1000+ lux for fine assembly, with low glare. Noise: hearing-conservation limits of 85 dB(A) over 8 h (3 dB exchange rate halves allowed time per 3 dB). Heat stress: WBGT indices set work/rest regimes. Vibration: hand-arm and whole-body exposure limits. Air quality and thermal comfort (PMV/PPD) affect performance.

Cognitive ergonomics and human error

Displays and controls should match mental models (compatibility), minimise workload (NASA-TLX), and support situation awareness. Human errors are classified as slips, lapses, mistakes and violations (Reason's Swiss-cheese model); design defences include error-proofing (poka-yoke), forcing functions, checklists, alarm management and automation with the human kept in the loop. Human reliability analysis (THERP, HEART) quantifies error probabilities for safety cases.

Formulas

Worked example: Lifting index

Given: RWL 9.1 kg, load 12 kg

Find: LI.

Answer: 1.31 — redesign recommended

Worked example: Shelf height

Given: Female overhead reach μ = 195 cm, σ = 8 cm

Find: 5th-percentile reach.

Answer: 181.8 cm → top shelf ≤ ~180 cm

Worked example: Noise exposure

Given: Workshop at 91 dB(A), 85 dB/8 h with 3 dB exchange

Find: Allowed time.

Answer: 2 hours

Revised NIOSH lifting equation

# Revised NIOSH lifting equation (metric)
LC = 23.0                       # load constant, kg
H, V, D, A = 40, 70, 60, 30     # horizontal cm, vertical cm, travel distance cm, asymmetry deg
FM, CM = 0.84, 0.95             # frequency (4 lifts/min, <1 h) and coupling (fair) multipliers
HM = 25 / H
VM = 1 - 0.003 * abs(V - 75)
DM = 0.82 + 4.5 / D
AM = 1 - 0.0032 * A
RWL = LC * HM * VM * DM * AM * FM * CM
for load in (8, 12):
    print(f"load {load} kg: RWL = {RWL:.1f} kg, lifting index = {load/RWL:.2f}")
# load 8 kg: RWL = 9.1 kg, lifting index = 0.88
# load 12 kg: RWL = 9.1 kg, lifting index = 1.31

Reaching 40 cm out, twisting 30° and lifting 4 times a minute cuts the ideal 23 kg limit to about 9 kg. The biggest lever is usually horizontal distance: bringing the load closer (H = 25 cm) would raise RWL by 60%. Tables give FM and CM for other frequencies, durations and grips.

Common mistakes

Applications

Key takeaways

Going further