|No Safety Case can be substantiated without systematic and thorough consideration of the human impact on the system. Synergy has developed, through its experience in the nuclear industry and defence arenas, a sequential procedure for full integration of human aspects within the development and substantiation of the Safety Case.
In our experience, it is important to make a proper consideration of human performance and identify where human error may affect safety by means of a thorough examination of task features such as procedures, interfaces, training and work organization.
Synergy has developed a structured and clearly auditable approach for assessing human performance issues in Safety Cases and other safety-related reports in a manner that is fully acceptable to the different regulators.
Synergy uses a seven-stage method for integrating human factors within the assessment of safety cases. This is an adaptable and flexible approach which has been applied successfully in various nuclear and defence settings. Close collaboration between the design engineers and ergonomists is assured because, at each stage, outputs are discussed and agreed.
Stage 1: Safety Goals Analysis
Undertaking a safety goals analysis ensures that the ergonomist has a complete appreciation of the system and that all the safety goals are fully considered. It provides an effective framework for presenting the safety assessment to independent assessors such as licensing authorities.
Stage 2: Derivation of Tasks and Scenarios
The Safety Goals Analysis identifies specimen scenarios for investigation. A key concept is the limiting scenario. This is a scenario that will illustrate the most extreme, credible challenges to safe operation and to human performance.
Key human elements to be considered in developing appropriate scenarios are the effects of stress, fatigue and compliance with procedures and rules.
Stage 3: Task Analysis
Hierarchical Task Analysis (HTA) is performed to provide a description of each safety critical process or activity. HTA focuses on the defined scenarios and shows how the identified safety goals are supported by a series of subtasks within a hierarchy. The analysis includes data relating to the working environment, interfaces, procedures, cognitive demands, group influences and time-related issues.
Stage 4: Qualitative Error Analysis
The tabulated tasks are then subjected to a Qualitative Error Analysis, which considers each, safety goal-related task individually in order to identify any potential human errors that may occur. Causes of error are considered, as well as the consequences and possible recovery actions.
Stage 5: Reconciliation/validation with the Design Safety Assessment
It is necessary to have a formal reconciliation between the human factors findings and the designed intent with regard to safety. At the very least, this comprises a discussion on the findings and the acceptance of any recommendations from the ergonomists.
However, it is likely that the existence of a Probabilistic Safety Assessment (PSA) will require that the human factors analysis is integrated within the PSA in the form of Human Reliability Assessments. This entails matching the human factors analysis to the structure of the PSA.
Stage 6: Human Reliability Assessment HRA
Actual calculation of human reliability proceeds based on the preceding steps. If the human reliability is shown to be unacceptably low, then designers and ergonomists will have to discuss and agree suitable modifications to the task management, training or procedures in order meet the PSA targets.
Stage 7: Development of Recommendations
Recommendations are now formally discussed and agreed. Synergy particularly insists on establishing a formal process for monitoring their implementation.
- Provided detailed human factors support to Safety Cases for the refit of Nuclear Submarines and the associated dockyard facilities.
- Carried out a number of studies to develop and support the safety cases for fuelling and refuelling at nuclear power stations.
- Proposed practical support in the development of the design Safety Case for an offshore production platform.