LESSON 4 - HUMAN ERROR

ERROR

Failure of a planned action to be completed as intended (error of execution) or use of a wrong plan to achieve an aim (error of planning). 

ERROR OF EXECUTION

Failure of a planned action to be completed as intended

ERROR OF PLANNING

use of a wrong plan to achieve an aim

ACTIVE FAILURES

• Occur at the level of the frontline operator  

• Effects are felt almost immediately.

LATENT CONDITIONS

• Tend to be removed from the direct operator control 

• Result in two kinds of adverse events: 

• Error provoking conditions within the local workplace (e.g., time pressure, understaffing, inadequate equipment, fatigue, inexperience) 

• Create long-lasting holes in defenses (e.g., design deficiencies, untrustworthy alarms, unworkable procedures).

PERSON APPROACH

• Blame the individual for forgetfulness, inattention, weakness 

• Countermeasures: write another procedure, disciplinary measures, threat of litigation, retrain, shame.

SYSTEM APPROACH

• Multiple faults that occur together in an unanticipated interaction create a chain of events in which faults grow and evolve. 

• Countermeasures: based on assumption that though we cannot change the human condition, we can change the conditions under which humans work (e.g., system defenses

Swain and Guttman’s (1980) Human Error Categories

1. OMISSION

2. COMMISSION

3. EXTRANEOUS ACT

4. SEQUENTIAL ACT

5. TIME ERROR

OMISSION

Portion of a task is skipped

COMMISSION

Task is performed incorrectly

EXTRANEOUS ACT

Task that should not have been performed, as it diverts attention from the system

SEQUENTIAL ACT

Task is performed out of sequence

TIME ERROR

Task performed too early, too late, or outside of time allowed

PLANNING

a goal is identified and a sequence of actions is selected to reach the goal

STORAGE

the selected plan is stored in memory until it is appropriate to carry it out

EXECUTION

the plan is implemented by the process of carrying out the actions specified by the plan

SLIPS: EXECUTION STAGE

• incorrect execution of a planned action

• example: miskeyed command 

LAPSES: STORAGE STAGE

• incorrect omission of a stored, planned action  

• examples: skipping a step on a checklist, forgetting to restore normal valve settings after maintenance

MISTAKES: PLANNING STAGE

the plan is not suitable for achieving the desired goal

Slips and lapses occur when:

■ the task is very familiar and requires little thought; 

■ people confuse two similar tasks; 

■ tasks are too complicated and long-winded; 

■ the main part is done but the finer details are missed; 

■ There are distractions and interruptions.

How to reduce slips and lapses:

■ make all workers aware that slips and lapses do happen; 

■ use checklists to help confirm that all actions have been completed; 

■ include in your procedures the setting out of equipment, site layout and methods of work to ensure there is a logical sequence; 

■ make sure checks are in place for complicated tasks; and 

■ try to ensure distractions and interruptions are minimized

WHY DO MISTAKES OCCUR?

■ Doing too many things at the same time. 

■ Doing too many complex tasks at once. 

■ Time pressures.

Factors which contribute to people making mistakes

■ The work environment 

■ Extreme task demands 

■ Social issues 

■ Individual stressors 

■ Equipment problems 

■ Organizational issues

GEMS: Generic Error-Modeling System

an attempt to understand the origins of human error

3 LEVELS OF COGNITIVE TASK PROCESSING

1. SKILL-BASED

2. RULE-BASED

3. KNOWLEDGE-BASED

SKILL-BASED

familiar, automatic procedural tasks

RULE-BASED

tasks approached by pattern-matching from a set of internal problem-solving rules

KNOWLEDGE-BASED

tasks approached by reasoning from first principles

Skill-Based Performance

What You're Doing At The Time: Very familiar, routine tasks that you can do without even thinking about it — like you're on auto-pilot. 

Errors We Experience 

• Slip - Without intending to, you do the wrong thing

• Lapse - Without intending to, you fail to do what we meant to do

• Fumble - Without intending to, you mishandle or blunder an action or word

Error Prevention Strategy

• Stop and think before acting

Rule-Based Performance

What You're Doing At The Time: Responding to a situation by recalling and using a rule that you learned either through education or experience

Errors You Experience

• Used the wrong rule - You were taught or learned the wrong response for the situation

• Misapplied a rule - You knew the right response but picked another response instead

• Non-compliance - Chose not to follow the rule (usually, thinking that not following the rule was the better option at the time)

Error Prevention Strategy

• Educate about the right rule

• Think a second time

• Reduce burden, Increase risk awareness, Improve coaching

Knowledge-Based Performance

What You're Doing At The Time: Problem solving in a new, unfamiliar situation. 

You come up with the answer by:  

• Using what we do know  

• Taking a guess  

• Figuring it out by trial-and-error  

Errors You Experience 

• You came up with the wrong answer (a mistake)

Error Prevention Strategy

• STOP and find an expert who or that knows the right answer

General Approach

• error-tolerance rather than error-avoidance 

• “It is now widely held among human reliability specialists that the most productive strategy for dealing with active errors is to focus upon controlling their consequences rather than upon striving for their elimination.”

Error Avoidance

Trying to prevent errors from happening in the first place.

Error Tolerance

Accepting that errors will happen and making sure they don't cause serious damage when they do.

BUILDING ROBUSTNESS TO HUMAN ERROR

• Discover and correct latent errors

• Increase system visibility

• Take errors into account in operator training

• Reduce opportunities for error (Don Norman)

Discover and correct latent errors

must overcome human nature to wait until emergency to respond

Increase system visibility

don’t hide complexity behind automated mechanisms

Take errors into account in operator training

• include error scenarios 

• promote exploratory trial & error approaches 

• emphasize positive side of errors: learning from mistakes

Reduce opportunities for error (Don Norman)

• get good conceptual model to user by consistent design 

• design tasks to match human limits: working memory, problem solving abilities 

• make visible what the options are, and what are the consequences of actions 

• exploit natural mappings: between intentions and possible actions, actual state and what is perceived, …

• design for errors. Assume their occurrence. Plan for error recovery. Make it easy to reverse actions and make it hard to perform irreversible ones.

• when all else fails, standardize: ease of use more important, only standardize as last resort 

ERROR PREVENTION TOOLS

• Job Hazard Assessment/Pre-Job Brief 

• Self Checking (STAR) 

• Peer Checking 

• 3 Legged communication 

• Situational Awareness 

• Questioning Attitude 

• Stop When Unsure

Job Hazard Assessment / Pre-Job Brief

• Identify existing and potential job site hazards 

• Identify how hazards will be addressed 

• Discussion with all job participants to ensure mutual understanding and to ensure all questions and concerns are addressed 

• Pre-Job Brief shall cover at least the following subjects: 

• hazards associated with the job 

• work procedures involved 

• special precautions 

• energy source controls 

• personal protective equipment requirements

S.T.A.R – Self Checking

• STOP – Is my attention focused on the task? 

• THINK – What action am I about to perform? 

• ACT – Am I performing correctly? 

• REVIEW – Did I get the expected results?

Peer Checking

• A “second set of eyes” to detect and prevent errors. 

• To be used when performing critical work prior to taking action.

Three-Legged Communication

• Used during the execution of critical steps to formalize communication. 

• Repeat-back should be used when speaking with Operating entities. 

• Ensures mutual understanding

Situational Awareness

• Continual assessment of surroundings 

• Recognize changes in job scope/conditions 

• Recognizing changes in behavior

Questioning Attitude

• Stop, look, and listen – proactively search for uncertain or unfamiliar situations 

• Gather information – ask questions… don’t assume

STOP When Unsure

• If you have a feeling that something is not right – STOP!

• If you are not sure of the course of action of the outcome of your actions – STOP!

Feedback and Reinforcement

• People achieve high levels of performance based largely on the encouragement and reinforcement received from leaders and peers.

SUMMARY

• Humans are critical to system dependability - human error is the single largest cause of failures 

• Human error is inescapable: “to err is human” - yet we blame the operator instead of fixing systems 

• Human error comes in many forms - mistakes, slips, lapses at KB/RB/SB levels of operation – but is nearly always detectable 

• Best way to address human error is tolerance - through mechanisms like undo