Alarm systems play an important role in the operation of complex process control settings. A reliable and user-friendly alarm system developed according to the operators' conditions contributes to maintaining safe and efficient operation. Many projects performed within the power generation industries are modernisations of legacy systems. The guidelines compiled to aid engineers and system developers when developing alarm systems mainly focus on new designs and are therefore only partially applicable in modernisation projects. Results and experience from seven theoretical and empirical research studies concerned with operator decision making and information needs in different working situations have been used to evaluate existing alarm system design guidelines (primarily NUREG-0700 and IEC-62241), in order to find out which alarm design guidelines are most important to consider in modernisation projects. The results indicate that general guidelines (e.g., use of an alarm philosophy) are essential for modernisation projects. However, detailed guidelines (e.g., colour coding and text size) should be used more carefully and with consideration taken to the existing design in the control room. The main conclusion is that, in many cases, the need for consistency between the new system and the existing system overrides the need to follow ergonomic design guidelines. The operators should not experience that they are using another system but instead only an extension and improved version of the existing system they already have. This paper summarises the principal guidelines to consider when modernising one's alarm system in hybrid control rooms.
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