Usually, a process step that is a Key Activity Type should be considered an actionable process step.
But if you want to prove/justify why such a process isn't an actionable process step, you can/should use the 3 fundamental elements method.
The fundamental elements process calculates a score for each of the three fundamental elements:
- public health impact,
- physical access to product and
- ability to successfully contaminate product.
The sum of the scores is compared to the FDA's recommended vulnerability ratings. If the score is sufficiently low, the process step can be considered to be NOT an actionable process step, one that does not require mitigation strategies.
Basically, if the tank is in a room that is always locked, then there will be a sufficiently low score for the element 'physical access to product' to say "We don't need (extra) mitigation strategies for this tank-holding operational step"
Note: I don't use the FDA's Plan builder software, I use the FDA Guidance document, but to the best of my knowledge, the methods and concepts are exactly the same.