1 May, 2023

Beyond Gantt Charts: How to Boost your Project with the Critical Chain Method

Every Project I ever led for clients, I delivered on time. And the secret: I used an approach called the Critical Chain Method (CCM). If you want in on how it works, read on…

The Israeli academic, Eliyahu Goldratt, introduced the Critical Chain Method in his 1997 book, Critical Chain’. This book, written in the form of a novel, take his core idea, ‘the Theory of Constraints’, and applied it to Project Management. The Theory of Constraints is the subject of his earlier business novel, The Goal’. That book focused on operational process improvement, by addressing resource constraints.

Critical Chain Project Management (CCPM) is a mash-up of the Theory of Constraints and the Critical Path Method (CPM) that was developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand.

This video explains the Critical Path Method:

Beyond Gantt Charts: How to Boost your Project with the Critical Chain Method

Explaining The Critical Chain Method

In this article, we’ll look at:

  1. The Big Idea behind Critical Chain Project Management
  2. A 7-Step Critical Chain Planning Process
  3. The Three Kinds of Critical Chain Buffer
  4. How I use the Critical Chain Method and the Benefits it Offers

Here goes…

The Big Ideas behind Critical Chain Project Management

There are two big ideas to understand in the Critical Chain Method:

1. Resource Focus

If you don’t have enough resources applied to an activity, it will cause a delay
This is a ‘resource constraint’. We normally think of human resource constraints – not enough time available from people with the right skills and capabilities. But this can equally apply to materials, tools, or equipment, or access to facilities like buildings, laboratories, or computing capabilities.

CCPM places a strong focus on understanding resourcing bottlenecks and planning our projects to minimize their impacts.

2. Contingency on Chains NOT Tasks

If you allocate contingency to each activity, you maximize the amount of contingency you need, while reducing the control the Project Manager has over the use of the contingency (or buffer) time.

CCPM clusters sequences of activities together and adds buffers, to reduce the risk of over-running.

A 7-Step Critical Chain Planning Process

Planning in Critical Chain Project Management starts with Critical Path Method. But it focuses on providing buffers against the use of constrained resources. Here is a seven-step process that I follow:

  1. Identify Project Activities
    Consider what work you need to do, to complete the project. We will usually do this using a Work Breakdown Structure (WBS). If you simply need to know what a WBS is, click here. If you want to know how to create a WBS, click here.
  2. Determine Dependencies to Create Network Chart
    Figure out which tasks are dependent on which, so you understand the sequence of linked tasks. We have a video to help you understand task dependencies – and the different types.
  3. Estimate Task Durations
    Now estimate the time it will take to complete each task. We have a guide to mastering Project Estimation skills.
  4. Determine Critical Path
    The Critical Path is the shortest route through the network. You’ll find our video on Critical Path Management above, near the start of this article.
  5. Identify the resources you will need to deliver your project
    Figure out what skills, expertise, materials, equipment, and other things you will need, for each project activity. We have a video on How to Deduce Project Resource Requirements
  6. Identify Constraints
    Which of your resources are likely to be limiting factors on your rate of progress? They may be in short supply, hard to access, or critical to your success.
  7. Create Buffers
    Build contingencies into your plan, to minimize the risks of delays arising from either slippage or non-availability of your critical resources. In the next section, I will describe the three types of buffers we have, in the Critical Chain Method.

The Three Kinds of Critical Chain Buffer

Formally, we can provide three kinds of buffers:

  1. Project Buffer
  2. Feeder Buffer (aka Feeding Buffer)
  3. Resource Buffer

Project Buffer

Project buffers add contingency time to the duration of the whole project. That is, they create a contingency period at the end of all project activities, before the milestone completion date. The term is also used for buffers at the end of a workstream.

Feeder Buffer

Feeder buffers ensure that non-critical tasks do not create delays that place the critical path at risk. They are contingencies added onto chains of tasks that feed into the main critical chain path.

Resource Buffer

Resource buffers create schedule buffers for tasks that either:

  • need to use scarce resources, or
  • could delay the start of work by scarce resources)

The term is also in use to refer to holding additional resources available for tasks that may be constrained by their resource level.

How I use the Critical Chain Method and the Benefits it Offers

This video starts with a recap of some of what you have just read. But, at around 2:45, I describe how I use an approach based on CCPM to deliver my projects on time, by creating buffers at the ends of each series of tasks.

This video is safe for viewing in the workplace.

Here is a copy of the illustration in the video.

The Critical Chain Method

I call these buffers either ‘Fire Breaks’ or ‘Islands of Stability’. These metaphors each capture some of the essence of why they work:

  • Fire Breaks are regions of woodland that firefighters will fell and clear to stop a forest fire from spreading. In our projects, these buffers mean that a chain of tasks can over-run their scheduled completion date, without affecting the start date of a succeeding chain of activities.
  • Islands of Stability refer to these buffers as periods when we can get our project into a stable configuration that matches our plan. If we finish before or during the buffer period, we can use the time for discretionary tasks or to get ahead on future activities.

You’ll see that the approach I take can apply to any of the three types of buffers.

Why this Method Works

This method works because the project manager is able to manage the contingency, rather than each team member. As PM, you gain a more strategic overview of contingency. This has implications for the psychology around the risks of over-run and also for the total contingency you need to apply.

The Psychology

This means that:

  1. If work is running late, team members do not need to feel stressed by the pressure of missing a due date. The PM can allocate time from the buffer to accommodate their overruns.
  2. If work is running ahead of schedule, team members no longer feel the incentive to expand the work to fill the time available (which is called ‘Parkinson’s Law’.)
  3. Since team members have no contingency within their control, they are accountable to the PM for any global contingency they will need to draw don on. This reduces the likelihood of student syndrome – the tendency to delay starting a task until the last possible moment.

Reduced Contingency

And, aside from these examples of simple psychology, there is another big advantage to this approach. In our example, we had 7 days of contingency. As a PM, you may not know which elements of that contingency you may need, but you might be confident that not all risks will materialize.

Over the course of a long enough chain, you can make a judgment to reduce the total project-level contingency. In this way, the Critical Chain Method can deliver both more confidence AND reduced schedule.

What are Your Thoughts on Critical Chain Project Management?

As always, I’d love to read your thoughts, experiences, and question. Put them in the comments below and I will respond to every contribution.

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Mike Clayton

About the Author...

Dr Mike Clayton is one of the most successful and in-demand project management trainers in the UK. He is author of 14 best-selling books, including four about project management. He is also a prolific blogger and contributor to ProjectManager.com and Project, the journal of the Association for Project Management. Between 1990 and 2002, Mike was a successful project manager, leading large project teams and delivering complex projects. In 2016, Mike launched OnlinePMCourses.
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