As I interact with people who participate in and manage shutdowns, I sometimes wonder if we really appreciate the true meaning of the term “critical path”. Yes, it is represented by the most important jobs on the shutdown, and you might be able to look at a list of tasks to be performed during the shutdown and guess at those that will be on the critical path with a medium level of accuracy. But can you identify it with any high degree of certainty? If you can identify it, what do you do with this knowledge?
I would characterize this knowledge as awareness but not expertise. I believe that there is much opportunity to be gained by using some simple tools to calculate and manage to the critical path of the shutdown. Not the “gut-feel critical path” but rather the “mathematically calculated critical path”.
The definition of the critical path is:
The shortest possible duration by which a set of tasks can be completed. It is represented by the longest summation of task durations given the required predecessor and successor relationships.
Let me take a moment to share with you 3 ideas that I feel every shutdown manager absolutely must know about their critical path.
Idea 1: It is not a guess. It is a calculated value.
Yes, as the name implies, the critical path of the shutdown is represented by the most important jobs. It defines the duration of the shutdown.
This duration, however, is the sum of the durations of the individual tasks based on the predecessor/successor relationships. It is not a guess. It is not a gut-feel. It is science.
Let me give you a quick illustration.
The diagram below shows a series of tasks labeled A through K (we tend to skip “I” when building such a diagram to avoid the confusion with the number 1). The bottom half of each block contains the duration for each individual task.
We can easily see the predecessor and successor relationships in such a diagram. Note that the node after tasks C and D represents a situation where both of these tasks must be complete before we can move on.
In this second diagram, I have illustrated the critical path for this set of tasks. It just happens to be 22 W (weeks).
That is it. End of argument. Unless we do something differently, the critical path for this set of tasks is 22 weeks. There are, of course, methods we can apply to change this, but at the moment no shorter than 22 weeks… and that is if everything goes perfectly.
Idea 2: It is the best method of prioritizing work for a shutdown.
Now that we know that the duration of this project (shutdown) is 22 weeks, we can start working on either shortening that or, at the very least, shoring up our ability to reach this target. Where should we begin with these efforts? Well, with those tasks that are on the critical path of course.
- It is likely that I will not be able to plan as thoroughly for every job on the shutdown as I would like, so let’s make sure that I put my best effort on those tasks that are on the critical path.
- I probably have limitations on the amount of labor I can bring in to support the shutdown, so let’s give priority to the critical path jobs.
- When preparing the materials I need for the shutdown, let’s put extra effort in the ordering, tracking, receipt inspection, and staging of those items needed for critical path jobs.
You get the picture.
Idea 3: The Critical Path is the closing bid on a negotiation for duration. Never take the first bid.
This one is important. So often I see people prepare for shutdowns that fit into a nice and neat window of time. One-week annual shutdowns, some multiple of days (3 days, 5 days) etc., etc.
When I see such a stated duration, I generally find that we perform a shutdown of this very same duration year in and year out. When I ask how we arrived at this duration, I generally receive an answer like, “That is what we always do.” This is one of the biggest flags you can look for in an improvement opportunity.
When we as leaders decide that we can afford a business interruption of 7 days for a maintenance shutdown, this must be considered the opening bid in a negotiation. What we really mean to say is, “We can afford up to 7 days, but would like to start up sooner if it is possible.”
Once we make this opening offer, we then task those people in charge of the shutdown to fill in the details. Develop a list of jobs to be done during the shutdown (the scope), estimate a time for each task, arrange these tasks into a schedule, and calculate the critical path.
We must expect that these people come back to us with another offer. If you offer a week (168) hours, then I would expect a counter offer such as:
- We can complete the needed scope in 143 hours.
- We really need 181 hours or we will have to start dropping some tasks out of our scope, which we really do not want to do.
Both are acceptable answers to me as it illustrates some real thought and preparation being put into the plan. Not a gut feel, but real thinking.
Building a critical path is not difficult. If you use only the base functionality of MS Project (Task Description, Duration, Predecessor), you can easily see a critical path when you view the network diagram. Take 5 minutes to recreate the plan I have shown you above in MS Project and you will see what I mean.
If you are not determining your critical path as a calculated value, and then managing to this critical path, you are leaving time and money on the table. Simple as that.
Best of Luck and Mahalo