For information, contact the Center for Chemical Process Safety at the American Institute of Chemical Engineers at the address shown above. David Embrey of Human Reliability Associates, with assistance from the CCPS Human Reliability Subcommittee.
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Manual variability An error mechanism in which an action is not performed with the required degree of precision (eg, timing, spatial precision, force). Slips Errors in which the intent is correct, but failure occurs while performing the required activity.
Introduction: The Role of Human Error in Chemical Process Safety
Scope and Organization
Chapter 1, The Role of Human Error in Chemical Process Safety, discusses the importance of reducing human error to an effective process safety effort at the plant. This chapter provides the reader with the underlying theories of human error needed to understand and apply a systems approach to their reduction.
Purpose of This Book
- Cross-Disciplinary Studies
- A Complement to Other CCPS Publications
A major goal is to provide engineers, managers, and process plant personnel in the CPI with an entirely new perspective on human error. Some of these are intended to illustrate the range of situations where human error has occurred in the CPI (see Appendix 1).
INPUTS
WHY IS HUMAN ERROR NEGLECTED IN THE CPI?
Despite this evidence, the study of human error has previously been a much neglected area of the industry. Human error has often been used as an excuse for deficiencies in the overall management of a facility.
BENEFITS OF IMPROVED HUMAN PERFORMANCE
The evidence presented in the preceding section makes it clear that human performance problems pose a significant threat to CPI safety. A major reason for the neglect of human error in the CPI is simply a lack of knowledge of its significance for safety, reliability and quality.
THE TRADITIONAL AND SYSTEM-INDUCED ERROR APPROACHAPPROACH
These aspects of the system-induced error approach are shown as the third circle in Figure 1.5. Thus, the dark area in the center of the model represents the possibility of uncovered errors with significant consequences.
A CASE STUDY ILLUSTRATING THE SYSTEM-INDUCED ERROR APPROACHERROR APPROACH
- Error-Inducing Conditions 1. Design and Culture Factors
- Error Tendencies
- Unforgiving Environment
The nature of maintenance operations had changed since the procedures were first written, but these changes were not incorporated. Because the technicians had not participated in the development of the procedures, there was no sense of ownership and no commitment to using the procedures.
FROM THEORY TO PRACTICE: TURNING THE SYSTEMS APPROACH TO A PRACTICAL ERROR REDUCTIONAPPROACH TO A PRACTICAL ERROR REDUCTION
- Performance Optimization
- Prediction of Human Error and Its Consequences
- Error Prevention (Audit Techniques)
- Learning Lessons from Operational Experience
- Influence of Organizational Factors
Another aspect of the unforgiving environment was the vulnerability of the system to a single human error. The next component of the systems approach is the process of learning lessons from operational experience.
APPENDIX: CASE STUDIES OF HUMAN ERROR LEADING TO ACCIDENTS OR FINANCIAL LOSSTO ACCIDENTS OR FINANCIAL LOSS
- Introduction
- Errors Occurring during Plant Changes and Stressful Situations
- Inadequate Display of Process Information Example 1.4
- Failures Due to False Assumptions
- Ineffective Organization of Work
- Failure to Explicitly Allocate Responsibility
The first set of case studies illustrates errors due to inadequate Human Machine Interface (HMI) design. Examination of the wreckage after the fire revealed that the pump suction valve was open and the pump discharge valve was closed.
Understanding
Human Performance and Error
PURPOSE OF THE CHAPTER
CONCEPTS OF HUMAN ERROR
- Engineering Concepts of Error
- Human Error in Accident Causation
- Summary of Definitions
In the case of hidden human error, the consequences of the error may only become apparent after a certain time, when the condition caused by the error is combined with other errors or special operating conditions. Latent human error/failure (operational level): Latent human error is similar to active error, but the consequences of the error may only become apparent after a certain time or in combination with other errors or special operating conditions.
AN OVERVIEW OF THE FOUR PERSPECTIVES ON HUMAN ERRORHUMAN ERROR
- Traditional Safety Engineering
- Human Factors Engineering/Ergonomics
- Cognitive Systems Engineering
- Sociotechnical Systems
- Conclusions
They all have a role to play in an integrated approach to managing human error to reduce accidents in the CPI. Moreover, despite the successes of the traditional approach in the field of occupational safety, it may be less applicable in areas such as the prevention of major chemical accidents.
THE TRADITIONAL SAFETY ENGINEERING APPROACH TO ACCIDENTS AND HUMAN ERRORTO ACCIDENTS AND HUMAN ERROR
- Accident Prevention from the Traditional Perspective
- Disadvantages of the Traditional Approach
- Safety Campaigns
- Disciplinary Action
- Safety Management System Audits
- Training
In such cases it is difficult to discern the effects of the incentive scheme alone. Four weeks after the application of the disciplinary approach, the use of the equipment had actually decreased.
THE HUMAN FACTORS ENGINEERING AND ERGONOMICS APPROACH (HF/E)
- The Human-Machine Interface
- Human Error at the Human-Machine Interface
- Perception
- Control Actions
- Information Processing and Mental Workload
- Automation and Allocation of Function
- The Deterioration of Skills
- System Reliability Assessment and Human Error
- Summary and Evaluation of the HF/E Perspective on Human Error in the CPI
The sensory input information is interpreted according to the worker's mental model of the process. Summary and evaluation of the HFE perspective on human error in CPI on human error in CPI.
THE COGNITIVE ENGINEERING PERSPECTIVE
- Explaining and Classifying Errors from the Cognitive Perspective
- The Skill-, Rule-, and Knowledge-Based Classification
- The Generic Error Modeling System (GEMS)
- Classification of Errors from the Cognitive Perspective 1. Slips and Mistakes
- Error Recovery
- The Stepladder Model
- How Can the Cognitive Approach Be Applied to Process Safety in the CPI?
- Error Prediction
- Summary of the Use of Cognitive Models in CPI Safety
In the event that the cause of the problem cannot be determined by applying an available rule, the worker may have to return to the knowledge-based level. If the nature of the problem is not clear, it may be necessary to go to the rules-based level.
Characteristics
Situational Characteristics
Task Performance
Influencing Factors
Conclusions Regarding Application of the Cognitive Modeling Perspective to Errors in the CPI
These topics have been addressed in some depth because they provide a comprehensive basis for reducing human error in CPI. The advantage of an analytical framework driven by a model of human error is that it specifies the nature of the questions that are needed.
THE SOCIOTECHNICAL PERSPECTIVE
- The TRIPOD Approach
- Human Factors Analysis Methodology
- The UK Health & Safety Executive Research Program on Sociotechnical Systems
- Comparisons among the Sociotechnical Approaches
These factors are broken down into a series of diagnostic questions that can be used to numerically assess the dimensions that make up the higher-level factors. HFAM has 20 groups of factors instead of the 10 general failure types of the TRIPOD approach.
SUMMARY
Although both systems are primarily aimed at preventing errors, they can also be used as part of the retrospective analysis of accidents that have already occurred. Nevertheless, the qualitative dimensions included in the audit trail will undoubtedly provide information that can be used as part of an error prevention program.
APPENDIX 2A: PROCESS PLANT EXAMPLE OF THE STEPLADDER MODELSTEPLADDER MODEL
This phase uses action rules of the form "if Y then do Z" as opposed to the diagnostic rules of the "Identify Plant Condition" box, which is the other component of rule-based processing. This box, which is self-explanatory, includes highly practiced actions in the skill-based domain.
APPENDIX 2B: FLOWCHARTS FOR USING THE RASMUSSEN SEQUENTIAL MODEL FOR INCIDENTRASMUSSEN SEQUENTIAL MODEL FOR INCIDENT
If the required response to the situation is obvious, that is, there are no alternative goals, then the sequence branches to the Select/Formulate Actions box, where the actions required to achieve the objective are formulated and then acted upon in the Execute Actions box. . Once you have decided on an appropriate target, the next stage is to plan how to get from the current state of the factory to the desired target.
APPENDIX 2C: CASE STUDY ILLUSTRATING THE USE OF THE SEQUENTIAL MODEL OF ERROR IN INCIDENTOF THE SEQUENTIAL MODEL OF ERROR IN INCIDENT
Based on the evaluation of the PIF in the situation, the internal error mechanism could be the adoption of a stereotype or a wrong orientation in space. The exact form of the external error mode will obviously depend on the nature of the task.
INTRODUCTION
This is a similar distinction to the probabilistic safety analysis (PSA) used in nuclear power and the quantitative risk assessment (QRA) used in CPI. In section nex4 of this chapter, several application areas for PIF analysis will be described.
APPLICATIONS OF PERFORMANCE INFLUENCING FACTORSFACTORS
There is another connection between the PIF concept and the sociotechnical assessment methods described in section 2.7 The checklists used in the TRIPOD methodology are essentially binary questions that assess whether the sets of PIFs that make up each of the general failure types are appropriate or not. The following sections will describe each of the PIF categories in turn, followed by examples where appropriate.
A CLASSIFICATION STRUCTURE FOR PERFORMANCE-INFLUENCING FACTORSPERFORMANCE-INFLUENCING FACTORS
It should be emphasized that the PIFs discussed in this chapter, although generally considered important by human reliability specialists, are not intended to be exhaustive in their coverage. It is recommended that the advice of an experienced human reliability or human factors specialist be sought when deciding which PIFs to cover in a specific situation.
OPERATING ENVIRONMENT
- Chemical Process Environment
- Physical Work Environment
The next four PIFs (noise, lighting, thermal conditions, atmospheric conditions) refer to the quality of the worker's environment. One of the more comprehensive studies of the effects of total hours of work was conducted after World War II by the U.S.
TASK CHARACTERISTICS
- Equipment Design
- Location/Access
- Labeling
- Personal Protective Equipment
- Control Panel Design
- Content and Relevance of Information
- Identification of Displays and Controls
This refers to the clarity of the meaning of instructions and the ease with which they can be understood. Control panel design, equipment design, and job aids and procedures are factors that change the requirements of the task to be performed.
OPERATOR CHARACTERISTICS
- Experience
- Personality Factors
- Type A versus Type B Personality Type
- Physical Condition and Age
In summary, the use of the RHT model for the CPI may be questionable. Job requirements will determine the general ability and age of the workers who will be hired for a particular job.
ORGANIZATIONAL AND SOCIAL FACTORS
- Teamwork and Communications
The oil spilled over the surface of the water in the pipe trench and the welders set it on fire. The extent of group planning and task orientation at the beginning of the transition process will determine the success of the overall performance.
INTERACTION OF PERFORMANCE-INFLUENCING FACTORSFACTORS
This is partly a result of the large number of possible PIF combinations and the complexity of their interactions. One of the most effective ways to study this interaction is through an in-company human factors study, which will use operational feedback to evaluate the results of design and human factors innovations.
VARIABILITY OF HUMAN PERFORMANCE DURING NORMAL AND EMERGENCY SITUATIONSNORMAL AND EMERGENCY SITUATIONS
Typically, such analyzes depend on the level of detail provided in the reports or the accuracy of the memory of the participants. The retrospective analyzes may also be subject to the effects of the rationalizing "hindsight" bias.
SUMMARY
Analytical Methods for Predicting and Reducing Human Error
INTRODUCTION
The third category of methods covered in this chapter is error analysis and reduction methodologies. Very often the distinction between task analysis and error analysis is blurred, as the error analysis process must always proceed from a comprehensive description of a task, usually derived from a task analysis.
DATA ACQUISITION TECHNIQUES
- Discussions and Interviews with "Experts"
- Observation
- Critical Incident Technique
- Documentation
- Activity Analysis
- Simulators and Mock-ups
- Withholding Information
Therefore, the workers should be informed about the objectives of the observational study in advance. An appropriate analysis of the task is necessary to determine the nature of the simulation to be used.
TASK ANALYSIS
- Purpose of Task Analysis
- Applications of Task Analysis
- Action Oriented Techniques 1. Hierarchical Task Analysis (HTA)
In the same way, the consequences of errors can be assessed in relation to the overall vulnerability to human error in the examined subsystem. Therefore, the extent of the final OAET will be a function of the analyst's experience.
Start
Exit
Cognitive Task Analysis Techniques
Cognitive task analysis techniques attempt to address the underlying mental processes that cause errors rather than merely surface forms of errors. The problems associated with the analysis of cognitive processes are much greater than with action-oriented task analysis methods.
