Human Performance and Limitations
The human in the loop
This domain covers hypoxia, hyperventilation, decompression, spatial disorientation, fatigue, stress, and decision-making. Understand the sensory systems (vision, vestibular, proprioception) and their limitations.
Key concepts
- Hypoxia types: hypoxic (altitude), hypemic (anaemia/CO), stagnant (G-loading), histotoxic (alcohol/drugs).
- Time of useful consciousness (TUC): decreases rapidly above FL 250.
- Spatial disorientation: the somatogravic and somatogyral illusions; the leans; graveyard spiral.
- Vision: foveal vs peripheral; night vision requires off-centre viewing and dark adaptation (~30 min).
- Fatigue and circadian rhythm: performance lowest 02:00–06:00.
- Stress and decision-making: recognise the DECIDE model and hazardous attitudes.
Traps
- Confusing hypoxic and hypemic hypoxia.
- Assuming hyperventilation causes hypoxia - it causes CO₂ washout with similar symptoms.
- Forgetting that alcohol impairs performance even below legal limits.
- Mixing illusion names (somatogravic = acceleration; somatogyral = rotation).
Worked example / rule of thumb
1 % COHb ≈ 1 % loss of oxygen-carrying capacity; smoking raises baseline COHb significantly. Rule of thumb: if symptoms of hypoxia appear, use supplemental oxygen immediately and descend.
Dark adaptation: avoid bright white light; use red lighting and off-centre viewing.