Human Factors
The framework
The SHELL model (Software, Hardware, Environment, Liveware) locates error at the interfaces between people and their workplace. Reason's Swiss-cheese model shows how latent organisational weaknesses line up with active errors to breach every defence. The "Dirty Dozen" - lack of communication, complacency, lack of knowledge, distraction, lack of teamwork, fatigue, lack of resources, pressure, lack of assertiveness, stress, lack of awareness and norms - is the standard list and appears repeatedly in questions.
The human
Fatigue and circadian rhythm (the early-hours trough around 0300–0600), hypoxia (subtle at first: euphoria and poor judgement), hyperventilation, spatial disorientation, vision (rods for night vision, cones for colour and detail), hearing damage, memory limitations, and the effect of stress and workload on performance. Complacency is most dangerous on routine, familiar tasks.
Practice
Communication through read-back and standard phraseology, situational awareness, teamwork, and error management through cross-checking and checklists. The classic trap is the drift into working from memory because "it always works".
The traps
Muddling the Dirty Dozen items; attributing an accident to a single cause; assuming fatigue only matters on night shift; forgetting that two independent defences are far stronger than one.
Worked example
Two independent defences each fail once in ten times; both failing is 1/10 × 1/10 = 1/100. Defence in depth multiplies reliability, which is exactly why dual inspection is required for critical tasks.