Human Failure Classification Flashcards
List the several types of errors; based on Rasmussens skill-rule and knowledge-based behavior theory.
SKILL-BASED ERRORS
Slips of Action
Lapses of Memory
MISTAKES
Rule-Based Mistakes
Knowledge-Based Mistakes
Briefly explain what is meant by Skill-Based Errors with examples
Also, how may we prevent these errors?
These types of errors occur in very familiar tasks which require little conscious attention.
Slips - Failures in carrying out the actions of a task. Examples include performing an action too soon or too late, leaving out a step or series of steps from a task, carrying out an action with too little or too much strength, performing the action in the wrong direction and doing the right thing but with regard to the wrong object or vice versa.
Lapses - Forgetting to carry out an action, losing a place in a task or forgetting what we had intended to do. These are often linked to interruptions or distractions. Using a simple checklist can help to reduce the likelihood of lapses occurring.
Possible prevention strategies include: Verification checks such as checklists, feedback, warning signals if wrong action is selected, design of routines to be distinct from each other and supervision.
Briefly explain what is meant by Mistakes with examples
Also, how may we prevent each of the errors that fall under the category of a mistake?
This failure involves our mental processes that control how we plan, assess information, make intentions and judge consequences.
RULE-BASED MISTAKES
These occur when our progrmme is based on remembering rules or procedures. We have a strong tendency to try to use or select familiar rules or solutions. Errors occur if no routine is known that will solve the new situation so we don’t know what to do, we try to apply the usual remembered rules and familiar procedures because of familiarity with similar problems from previous experience, even when they are not appropriate; or the wrong alternative is selected or there is some error in remembering to perform a routine.
Possible prevention strategies include: Simple, clear rule sets; systems designed to highlight unusual or infrequent occurrences; clear presentation of information.
KNOWLEDGE-BASED MISTAKES
These may occur in unfamiliar situations where no tried and tested rule exists. They are often related to incomplete information being available. Errors occur when some condition is not correctly considered or thought through or when the resulting effect was not expected or ignored, there is insufficient understanding or knowledge of the system or there is insufficient time to properly diagnose a problem.
Possible prevention strategies include: Training, supervision, use of checking systems, provision of sufficient time and knowledge.
Briefly explain what is meant by Violations
Violations are a deliberate deviation from a rule or procedure.
Briefly explain the three types of violation with examples.
ROUTINE VIOLATION
A routine violation is the normal way of working within the work group. Examples include: Cutting corners to save time and/or energy, perception that rules are too restrictive, impractical or unnecessary, belief that the rules no longer apply, lack of enforcement of the rules and new workers starting a job where routine violations are the norm and not realizing that this is incorrect.
SITUATION VIOLATIONS
This is where the rules are broken due to pressures from the job such as: Time pressure, insufficient staff for the workload, the right equipment not being available and extreme weather conditions.
EXCEPTIONAL VIOLATIONS
These rarely happen and only occur when something has gone wrong. To solve a problem, employees believe that a rule has to be broken. It is falsely believed that the benefits outweigh the risks. Means of reducing these violations include: Training for dealing with abnormal situations, risk assessments to take into account such violations and reduction of time pressures on staff to act quickly in new situations.
When decisions are made during any working situation they are either on-line or off-line processing. Explain the differences
ON-LINE PROCESSING
Decisions which have to be made as a work process is in operation.
OFF-LINE PROCESSING
Decisions which can be made after consideration of a number of alternatives.
Rasmussen’s model suggests three levels of behavior that explain the human error mechanisms. Explain these levels
SKILL-BASED BEHAVIOR
A person is carrying out a tried and tested operation in automatic mode.
RULE-BASED BEHAVIOR
Operator has available a wide selection of well-tried routines
KNOWLEDGE-BASED BEHAVIOR
Person has to cope with unknown situations where there are no tried rules or skills
Explain the Kegworth Air Disaster
A boeing 737 airliner takes off on a routine flight from London to Belfast - Previous problem with vibration in the right-hand engine - Maintenance log evidences this had been attended to - Pilot reads maintenance log before take off - Air conditioning is driven mainly from the right-hand engine - Pilot experiences vibration and an excess of smoke and fumes during flight so throttles back the right-hand engine - Smoke and vibration stops - This was a coincidence but eased the pilot in thinking he had handled the problem - The right engine was shut down - A warning light may have shown there was a fire in the right-hand engine - Pilot obtained permission to land at East Midlands Airport - It was then found that the wrong engine had stopped and the problem was actually in the opposite engine which had suffered a turbine blade detachment - The pilot would have little difficulty landing the plane with one engine but had to land it on one FAULTY engine - Pilot crashed 900m short of the runway
List the key factors leading to the Kegworth Air Disaster
Inadequate training of flight crew to deal with the initial problem
The crew did not deal with the initial engine problem in accordance with what training they had
Other crew on board observed the flames from the left-hand engine but did not inform the flight crew
Explain the Piper Alpha North Sea Oil-Rig Explosion
1988 - Fire on the Piper Alpha Oil Rig - 167 men killed and many who survived were injured and traumatised.
Rig was operated by Occidental Petroleum Limited - Piper Alpha was part of a linked operation involving four rigs - Operation involved gas, compressed gases and crude oil - Various operations on Piper Alpha were in modules which were stacked on top of each other - Helicopter landing pad was on the highest level and on top of the main accommodation module - 226 men were on the platform and 62 were working the night shift and the majority were in the accommodation modules
10pm there was an explosion followed by a fireball that started from the west end of B module - This was followed by a series of smaller explosions. The emergency systems and fire water systems failed to operate - Three mayday calls were sent out and the personnel assembled on D deck - Radio system and the lighting then failed.
10:20pm there was a rupture of the gas riser of the Tartan supply followed by another major explosion with ignition of gas and crude oil.
At 10:50pm there was a further explosion with a collapse of much of the structure.
List the key factors leading to the Piper Alpha North Sea Oil-Rig Explosion
Failure in the permin-to-work system
Design failure in that the rig containment wall was fire-resistant but not blast-resistant
Other rigs did not shut down and continued to feed into Piper Alpha, fueling the fire
Inadequate emergency procedure for rig evacuation
Explain the Herald of Free Enterprise
The “Herald of Free Enterprise” sailed from Zeebrugge harbour for Dover with both inner and outer bow doors open - Water flooded in, causing the ferry to capsize - The assistant bosun was responsible for closing the doors but had fallen asleep - The Captain assumed that the doors were closed unless told otherwise - There was pressure on ferries to sail as quickly as possible.
List the key factors leading to the Herald of Free Enterprise incident
Design failings, in that roll-on, roll-off ferries were inherently unsafe and top-heavy
Reduction in the complement of officers, with long working schedules
No automatic monitoring of critical areas such as the bow doors
Poor emergency procedures, particularly provision of life jackets
Explain the Ladbroke Grove (Paddington Rail Disaster)
1999 a local passenger train passes a red signal and continues into the path of a high-speed train.
Joint investigation by the HSE and British Railway Police identifies a number of significant problems associated with the signalling system.
Among the problems was the positioning of a particular signal that was exceptionally difficult to read in comparison with other signals - It was also suggested that the drivers perception could have been affected by the sun reflecting on the signal lenses.
Additionally, there was debate about whether the Automatic Warning System could have given misleading warnings which led to them being disregarded.
One of the main conclusions was that the misinterpretation of the information presented by the signal was a significant factor. The competent of the driver was not questioned as he had been fully trained, although he was relatively inexperienced.
Explain the Three Mile Island (USA) disaster
Three Mile Island Nuclear Plant is near Middletown in Pennsylvania, USA.
1979 the reactor core went into meltdown - Only small releases of radioactivity and no deaths or injuries - The reactor was a pressurized water reactor which is a very common design - The primary water coolant water is kept pressurized so that it does not boil - The primary coolant water passes the heat on to a secondary water system which is allowed to boil - the steam driving the turbine to generate electricity
The incident started with a failure of the secondary circuit which prevented heat removal - This caused the reactor to shut down and the pressure in the primary circuit to increase - This triggered the opening of a pressure relief valve which stuck open instead of closing again when the pressure had reduced - The signals on the operating console indicated that the valve had shut - The continued escape of the coolant through the valve allowed the core to overheat.
Along with this was the confusing instrumentation available to operators - there was no coolant level indicator - instead it was inferred from levels elsewhere in the system which levels had raised by bubbles of steam - Alarms began to sound but at that point the nature of the unfolding incident was not recognised as a loss of coolant incident - Immediate actions included reducing the coolant flow in the core which made things worse - If they had done nothing, the plant would have cooled down on its own, instead the core continued to overheat and the fuel began to melt.
