What is Combined Capacity?

Workload is fatiguing. The longer you are on shift, the more tasks you need to complete, the more difficult the tasks are… even thinking about it makes me want to take a nap. Even if you slept well the night before, working hard (or hardly working) can leave you feeling drained. Why is that?

Let’s compare your brain to your smart phone. In this metaphor, the battery level of the phone represents your Sleep Reservoir. A fully charged phone roughly equals a fully rested person. Let’s say your WIFI router at home has limited range, and so, your phone works faster in some rooms of the house compared to others (I’m looking at you, basement-level guest room). The rooms of your house where your phone works more slowly regardless of how well the battery is charged is similar to how your brain works more slowly at different times of the day, like the Window of Circadian Low (WOCL). In SAFTE-FAST, the metric Effectiveness describes how well you work as a function of Sleep Reservoir (battery level) and time of day (distance from your router). Workload is how much you are using the phone. You may have noticed that your phone works more slowly or overheats if you have a lot of apps open. The battery drains quickly too.

If your phone is working poorly, you are likely to check the battery level, consider your distance from the router, and see how many apps you have open. Checking all these different factors can help you figure out if you need to plug your phone in, move closer to the router, or close some apps in order to improve performance. In terms of alertness predictions in SAFTE-FAST, this would be like checking Sleep Reservoir, Effectiveness, and Workload to see why performance is poor. In operations, it is not uncommon for high workload and low alertness to co-occur, creating a compound fatigue risk. Poor performance may be due to a combination of factors and so it is important to check each factor to see how they may be contributing to the problem of fatigue. Ok, but what if I just want to check ONE metric for performance that takes all those factors into consideration?

Your phone doesn’t provide a singular predictive metric for performance, but SAFTE-FAST does. Combined Capacity is a recently added metric in SAFTE-FAST that indicates areas of high compound fatigue risk. The Combined Capacity metric represents cases in which work demands exceed the operator’s computing capabilities. Combined Capacity is an average of Effectiveness, Sleep Reservoir, and Workload. Effectiveness, Sleep Reservoir, and normalized Workload all use a 0 to 100 point scale. However, while higher scores (i.e., 100) indicate greater capacity and lower fatigue risk with Effectiveness and Reservoir, the opposite is true of Workload. Higher scores in the Workload metric indicates more demand on the worker. To reconcile the differences in scale directionality between Effectiveness, Reservoir, and Workload, the Workload scale is inverted when computing Combined Capacity. Thus, low Combined Capacity scores indicate cases of high compound fatigue risk.  Higher scores for Combined Capacity (i.e., 100) indicate greater capacity and lower fatigue risk while lower scores (i.e., 0) indicate diminished capacity and higher risk.

Combined Capacity represents fatigue risk in relation to “overload”, or too much work, in combination with low alertness. High workload alone is seldom a fatigue hazard if a person is alert and able to handle work demands. Relatively high workload is a fatigue risk when it is combined with relatively low alertness, represented by low Effectiveness and Sleep Reservoir. There is also risk associated with “underload”, or too little work. A crew member who has too little to do can become bored or disengaged. To use the phone metaphor, the screen goes black if you aren’t scrolling around on it. Underload can be problematic even if Effectiveness and Sleep Reservoir are high. For these reasons, Combined Capacity is not a good metric to use if you are trying to identify risk in relation to underload. We are still working to develop a proper metric for estimating the risk associated with underload in SAFTE-FAST.

If you are interested in learning more about the science behind Combined Capacity and how you can use it in SAFTE-FAST as part of your fatigue risk assessments, you’re in luck! The Combined Capacity White Paper is available on the SAFTE-FAST website here. If you have questions about Combined Capacity or the other ways that SAFTE-FAST is working to incorporate workload into fatigue risk predictions, please use our contact form at https://www.saftefast.com/contact-us, reach out to your SAFTE-FAST representative, or a member of the IBR science team. We will be happy to chat about it!

If you’re having problems how your smart phone is performing, then please ask your service provider instead of us!