What is Critical Chain and Why Are Buffers So Important? 

William Delaney

A project management team meeting

Some things never change, and the project management world is no exception to this rule. Every time a project manager takes on a new project, the age-old race against the deadline begins.

To tackle this problem, good project managers plan with a buffered duration period. This tactic aims to ensure the security of the scheduled end date – but this “safety” is not guaranteed and often projects are delayed anyway. Why? Usually these delays are caused by various bottlenecks, or unexpected issues that arise throughout the course of the project.

Critical chain project management – also known as “CCPM” – is an extension of the theory of constraints. In layman’s terms, it involves identifying bottlenecks and potential risks at the beginning of a project, and tackling them head-on to increase the throughput (delivery). This protects both the quality of the project deliverables and its schedule.

Effective CCPM is centred around three fundamental areas: Planning, management and resource allocation. CCPM has many advantages, the foremost being that it speeds up the delivery time, allowing for more projects and boosting business goals – satisfying customers and stakeholders alike.

The critical chain in a nutshell is the longest path to deliver on project goals (time) taking into consideration interdependence and resource constraints. Always remember that the CCPM method has adapted the mandatory requirement of considering available resources directly form the critical path method.

Critical chain is an advantageous methodology, but the main leg-up it has on other traditional project management concepts, like Waterfall, is how uncertainties are catered to. The more traditional PM methods tend to push back the ultimate deadline, but start individual tasks at the same time. From here they try to solve any unexpected problems that happen to pop up.

Critical chain takes a different approach. Uncertainties are managed by scheduling an approximate time for the completion of each individual task and leaving out any unnecessary tasks to reduce time to delivery.

Buffers are added to key tasks during the planning phase to ensure the protection of the entire project. Then, buffer management comes into play, enabling the PM to have full control of the project.

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When using CCPM, professionals in the field would break down the usage of buffers into three different categories:

  • Project Buffers
  • Feeding Buffers
  • Resource Buffers

Let’s break these buffer types down!

Project Buffers

Project buffers are generally known as the dominant buffer. They’re placed between the final task within a project and the scheduled end date. This buffer is used as a safety net for each activity within the project. Delays that could potentially arise due to constraints will eat into the buffered time, but the project completion date will remain the same. On the other side, if any task happens to finish early, this spare time will be added to the project buffer.

Usually this buffer type would be estimated at 40% of the contingency durations taken from each individual task. But once this project moves to the execution phase this buffer is then fixed and cannot be moved.

Feeding Buffers

Any additional path merging into the critical chain is known as a feeding chain. This is where the feeding buffer jumps in. The feeding buffer is used as a security measure to protect the critical chain from any threats within the feeding chain(s).

Similar to their big brother (the project buffer) feeding buffers are placed between the final task on the feeding chain and the main activity on the critical chain. When identifying the durations for the feeding buffer, you can calculate it with the same approach as the project buffer.

Resource Buffers

Resource buffers are used in parallel with the critical chain to ensure the necessary resources (personnel/equipment) are available for the completion of the task.

When it comes to project management, predicting perfection is a far off fantasy, but planning for difficulties is essential to fulfilling your quest in leading a successful project completion.