stress, workload and human error Flashcards
outline the aims of HF
- improve safety
- improve performance
- improve satisfaction
what is human error
HE is failure of a planned action to achieve the desired goal, without the intervention for the unforeseen event.
the errors are therefore inevitable and a price paid for human ability to cope with complex tasks.
is human error a cause or contribution for accidents
- HE is a factor of many incidents but not often the reason it occurred.
- many complex systems involve people in their operation so it isn’t surprising human error is a constituent.
discuss the type of human errors
errors of commission -> where an operator does something but the action is problematic.
slips -> when the action is not intended, a switch moved up instead of down on a plane.
errors in omission -> operator fails to do something, i.e., medical equip left inside a patient.
how are things designed for error
- good design can help minimise errors and thus consequences
in a bid to reduce error the design of ‘forcing functions’ is present, what is this?
there are 3 types:
inter-locks -> force sequences of events, microwave turns off when opened.
lock-ins -> stop someone carrying out actions, computer won’t turn off if work is unsaved.
lock-outs -> stop activities, basement stairwells are designed to stop you entering them in emergencies.
outline the cognitive factors in human error
perception - expectations
STM 7 +/- 2 is the limit, memory decay
LTM - incomplete retrieval
execution - motor co-ordination is poor
attention - loss of SA, tunnel vision
what are latent failures in human error
- these are failures made by those whose tasks are removed in time from operational activities.
poor conditions, poor training, poor job support all lead to latent failures.
what are performance influencing factors
- characteristics of the job, the individual and the organisation that influence error.
- optimising performance influencing factors reduces the occurrence of errors.
discuss stress as a cause of human error
- stressors inhibit someones ability to complete a task well.
- stress is linked to cognitive appraisal, pro climber see mountain as a challenge and novice see it as a threat.
environmental stressor - noise, vibration, heat
psychological stressors - anxiety, fatigue, anger
what are the 4 effects of stress
psychological experience - frustrations
psychological change - increased HR
stressors affect info processing - degrading performance
stressors have long term health consequences
how does workload cause human error
- humans have limited processing capacity and task performance requires this
- the resources a person has available is different to that of what a task requires
case study: Ladbroke Grove train crash, London 1999
immediate cause:
- signal SN109 at red, Tain accelerated beyond the stop signal into path of oncoming train, too late to avoid collision
automatic warning system (AWS)
- system warns drivers of signal ahead with audible and visual alerts
- alerts have to be actively cancelled, if not cancelled automatic brake is applied.
signal was unusual shape and offset from track, had history of SPAD - signal passed at danger
was sunny so hard to see signal clearly.
the driver on one train was newly qualified and had a shortened training schedule.
slough signal staff didn’t activate the emergency all stop protocol to drivers.
training was improved, and an overhaul of safety processes was conducted.
the rail safety and standards board was created.
