Creating an ASM-compliant HMI goes deeper than screen color selection
Operator situation awareness
The vision of the ASM Consortium is: operating teams who are empowered and enabled to proactively manage their plants, maximizing safety and minimizing environmental impact while allowing the processes to be pushed to their optimal limits. The overriding objective for effective operator HMI design practices is to enable the operator to manage manufacturing processes proactively, optimizing the plant performance while simultaneously preventing the occurrence of abnormal situations. Moreover, when abnormal situations do occur, the objective is to enable the operator to recognize the current situation, quickly bring the plant to a safe state, and then return the plant to normal operations.
The link between proactive operations and the console operator HMI is the operator's situation awareness. Continually updating operator situation awareness, understanding the state of the process and equipment, and, as a result, taking appropriate control actions-before alarm limits are reached-is the essence of being proactive. Providing effective operator HMI design practices that establish a high level of operator situation awareness is a necessary step for operating companies to enable a proactive operating posture.
Endsley characterized three stages of situation awareness:
- Perceiving information and changes to that information
- Understanding the status of the process and implications for any deviations, and
- Predicting where the process is moving and how much time is available to respond.
A key psychological construct in Endsley's model of situation awareness is the mental model. Rasmussen and colleagues have demonstrated that human experts working in complex systems possess a mental model that includes varying levels of abstraction and detail. They demonstrated that human experts move back and forth between varying levels of abstraction and detail, described as hierarchy of knowledge about how the complex system functions and what equipment is composed of, when performing their required work activities.
An ASM-compliant HMI intentionally defines display types at different levels of the mental model hierarchy, creating a display hierarchy that matches this mental model. Moreover, as shown in Figure 4, these display types all have a home in the overall HMI design so an operator can simultaneously move between the information in each type of display, consistent with human factors research on mental models. Providing ample access to trended information also supports the operator's ability to be proactive, predicting where the system is going, and how quickly, consistent with both human factors theories on situation awareness and mental models.
The benefits of providing an ASM-compliant HMI have been demonstrated in a controlled comparison using professional petrochemical plant operators using their own high-fidelity simulator of their actual plants, where the overall ASM systems approach to the DCS HMI led to 41% faster completion times, 36% more accurate diagnoses, and 380% greater detection of a process disturbance before the first alarm.
More recently, ASM Consortium research has demonstrated the benefits of span-of-control overview displays built using qualitative, at-a-glance gages and the benefits of qualitative trend indication for improving better operator situation awareness.
HMIs and effective operator interaction
Fast, error-free navigation through the display hierarchy and interaction with the DCS itself are critical to operator performance, not to mention critical to effective proactive operations. An ASM-compliant HMI provides on-screen navigation that reflects overall display hierarchy, as well as clear indications for where the operator is in the overall hierarchy and for critical alarm conditions, whether the ASM best practice linked navigation is implemented or an industry-typical drill-down navigation (Figures 5 and 6).
An ASM-compliant HMI also supports fast operator input. In the case of control adjustments on a single tag, the HMI provides dedicated locations where the faceplate will open (Figure 7). At the same time, the HMI also provides a home for Level 4 displays, where an operator could interact with predetermined sets of controllers, selectors, and indicators (Figure 8). These sets might be based on cascaded control loops, for example, or pulled together from different Level 3 displays to support specific activity (e.g., fired heater pilot gas, fuel gas, and pass flow controllers to support heater start-up).
Operator interaction also involves windows management, such that operators are not required to move pop-up displays and faceplates around, resize windows, close windows, and so on. Systems that use sufficient tools or minimal scripting without such tools eliminate the need for operators to divert their mental energy and attention away from the plant processes to do this windows management on their own.
Fundamental design principles
Two fundamental design principles that characterize an effective role of the operator HMI in improving the operators' ability to adopt a proactive operating posture include:
- The operator interface allows operators to develop and maintain a high level of real-time awareness of the state of the process under their control, while also allowing them to work at a very detailed level in performing specific operations on individual process units and equipment.
- The operator interface allows operators to focus their mental resources on controlling the process, not on interacting with the underlying system platform. That means the HMI is consistent and easy to use in terms of making minimal demands on the console operators' mental and physical resources to understand and interact with the process control system.
While color use is critical to supporting the latter design principle, other ASM guidelines need to be implemented to deliver an ASM-compliant HMI. An HMI design based on an effectively defined display hierarchy, a multi-screen / multi-window approach-and not a single display / single window approach, simultaneous access to display levels in the display hierarchy, effective navigation, and interaction support is also necessary in achieving ASM compliance, and not just a gray-scale display that only uses color for alarm indication.
Dal Vernon Reising, PhD, and Peter Bullemer are consultants for Human Centered Solutions, an Abnormal Situation Management Consortium associate member company.
- HMI designers often believe, incorrectly, that ASM HMI guidelines only deal with color selection.
- Effective HMI design has to begin with understanding the factors that affect how humans interact with control systems.
- ASM guidelines, when implemented effectively, can facilitate major improvements in operator response time and decision-making accuracy.
Read more about ASM HMI guidelines at www.controleng.com and see related articles below:
Bullemer, P., Reising, D. V., Burns, C., Hajdukiewicz, J., & Andrzejewski, J. (2009). Effective Console Operator HMI: ASM Consortium Guidelines. ASM Consortium: CreateSpace Independent Publishing Platform.
Bullemer, P., & Reising, D. V. (2013). Effective Console Operator HMI: ASM Consortium Guidelines. ASM Consortium: CreateSpace Independent Publishing Platform.
Endsley, M. R. (1995). Toward a theory of situation awareness in dynamic systems. Human Factors, 37(1), 32-64.
England, J., & Reising, D. V. (2013). Successes & Challenges for Designing Effective Level 1 and Level 2 Displays. Presentation to the Honeywell Users Group America, Phoenix, AZ. June 17-20.
Errington, J., Reising, D. C., Bullemer, P., DeMaere, T., Coppard, D., Doe, K., & Bloom, C. (2005). Establishing human performance improvements and economic benefit for a human-centered operator interface: An industrial evaluation. In Proceedings of the Human Factors and Ergonomics Society 49th Annual Meeting (pp. 2036-2040). Santa Monica, CA: Human Factors and Ergonomics Society.
Goodstein, L. P., Andersen, H. B. & Olsen, S. E. (Eds.). (1988). Tasks, errors, and mental models. London: Taylor & Francis.
Rasmussen, J., & Jensen, A. (1974). Mental procedures in real-life tasks: A case study of electronic trouble shooting. Ergonomics, 17, 293-307.
Rasmussen, J., Pejtersen, A. M., & Goodstein, L. P. (1994). Cognitive Systems Engineering. New York: John Wiley & Sons.
Tharanathan, A., Bullemer, P. T., Laberge, J., Reising, D., & Mclain, R. (2010). Functional versus schematic overview displays: Impact on operator situation awareness in process monitoring. In Proceedings of the Human Factors and Ergonomics Society 54th Annual Meeting (pp. 319-323). Santa Monica, CA: HFES.
Yin, S., Wickens, C. D., Hong-Xiang, P. and Helander, M. (2011): Comparing Rate-of-Change Cues in Trend Displays for a Process Control System. In Proceedings of the Human Factors and Ergonomics Society 55th Annual Meeting (pp. 394-398), Santa Monica, CA: HFES.
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