Design of alarm systems in Swedish nuclear power plants

Research within the area of improving alarm system design and performance has mainly focused on new alarm systems. However, smaller modernisations of legacy systems are more common in the Swedish nuclear industry than design of totally new systems. This imposes problems when the new system should function together with the old system. This project deals with the special concerns raised by modernisation projects. The objective of the project has been to increase the understanding of the relationship between the operator's performance and the design of the alarm system. Of major concern has been to consider the cognitive abilities of the operator, different operator roles and work situations, and varying need of information. The aim of the project has been to complement existing alarm design guidance and to develop user-centred alarm design concepts. Different case studies have been performed in several industry sectors (nuclear, oil refining, pulp and paper, aviation and medical care) to identify best practice. Several empirical studies have been performed within the nuclear area to investigate the operator's need of information, performance and workload in different operating modes. The aspect of teamwork has also been considered. The analyses show that the operator has different roles in different work situations which affect both the type of information needed and how the information is processed. In full power operation, the interaction between the operator and the alarm system is driven by internal factors and the operator tries to maintain high situation awareness by actively searching for information. The operator wants to optimise the process and need detailed information with possibilities to follow-up and get historical data. In disturbance management, the operator is more dependent on external information presented by the alarm system. The new compilation of alarm guidance is based on the operator's varying needs in different working situations and is applicable in modernisation projects. The division of the guidelines has been performed according to which part of human-machine-interaction they touch upon (e.g., control room layout, user interface design, navigation or support function) and in which design stage (e.g. conceptual design or detailed design) they are relevant. The results indicate that general guidelines (e.g. use a documented alarm philosophy) are very important to consider and define to ensure consistency between different modernisation projects. Further, the requirement on consistency can override detailed guidance on e.g. colour coding or font size. The operators in the control room should experience the system as one system. In connection to modernisations it is also of outmost importance to consider the operator's existing knowledge and experience. The guidelines have been used for the development of a new alarm design concept. The new concept tries to indicate relevant information clearer than existing systems; it integrates information to a larger extent and has better connections between events, objects, alarms, and procedures. The developed concept should be evaluated and validated by operators in usability tests. The most important aspects to consider in modernisation projects are: - Future systems must be more flexible and offer possibilities to adapt to varying needs of information in different operational modes and work situations. - The cognitive and physical abilities of the operator should not be exceeded. - Reliable work procedures acquired by practice are difficult to change and should be retained. Tasks performed often and/or in quiet conditions should be changed to obtain higher efficiency. - The alarm system should be well integrated in the overall instrumentation and control system in the control room. - A documented alarm philosophy is needed to ensure consistency between different projects. - The alarm system should guide the operator to the relevant information and should facilitate early detection of deviations. - Every alarm should require a response. The intention with the developed design concepts is to facilitate for the operator to detect and correct deviations before alarms occur. If alarms occur, the aim is to better support and guide the operator independent of operating mode and thus to increase the possibilities for correct situation management.