Determination of control operator workload is of interest beyond the process control community. For the U.S. Navy, the workload of interest was how many Tomahawk Tactical Cruise Missiles one person could monitor and control.
These missiles are no longer fire-and-forget, but can be re-targeted mid-flight based upon changing situational dynamics. The Navy’s original estimate, an acknowledged “best guess,” was that an operator could handle four missiles. It turns out they were wrong by about a factor of three.
Researchers from MIT and the University of Virginia conducted an experiment to quantify performance for different numbers of missiles under the operators’ span of control (Cummings, M.L. and Guerlain, S. “Developing Operator Capacity Estimates for Supervisory Control of Autonomous Vehicles,” Human Factors, Vol. 49, No. 1, Feb. 2007, pp.1-15.)
Little difference was seen in controlling either 8 or 12 missiles; however, significant degradation was seen when attempting to control 16 missiles.
The results mirrored results for air traffic controllers that saw ten aircraft as manageable, but 17 too many. The research also affirmed that 70% utilization appears to be a valid threshold for upper levels of workload.
The impact of too low workload was seen when utilization fell below 40%, with optimal performance between 50-60%.
Does one hydrotreater equal one missile? Or does one reactor? The answers to those are open to speculation; however, Beville has long utilized 60% as the target for console operator loading, a value that is re-affirmed by this study.
In addition, humans are in some cases far more competent and capable than the “best guess” of the experts. Finally, the answer to the question, “How much can a person handle?” is not beyond the ability of the human factors community to measure.
RELATED EXTERNAL MEDIA
|Consortium Reports New Findings on Alarm Rates||Automation World|
|How Many Alarms Can An Operator Handle||Chemical Processing|
|Impact of Alarm Rates and Interface Design on Operator Performance||Automation World|
|Operator Interfaces: Moving from Comfortable to Most Effective||Automation World|
|Operator Performance as a Function of Alarm Rate and Interface Design||Mesa.org|
The dates for this year's Fall meeting for the Center for Operator Performance will be announced soon. For more information, please contact Lisa Via. Guests are always welcome!
Our summer newsletter is now available. Click here!
Take our short survey on operator span of control. Click here (new window)
David Strobhar's book, "Human Factors in Process Plant Operation," is now available in both hardcover and Kindle e-book.
Copyright © 1996-2017 Beville Engineering, Inc. All rights reserved. (937)434-1093. Beville@Beville.com