The critical chain method is one of the key tools and techniques for developing a project schedule.
To understand Critical Chain we have to look at how a project schedule is developed?
Creating a satisfactory project schedule is often takes lots of iterations.
Read More: The Critical Path Method
Developing a Project Schedule?
We have to go through steps during the development of a schedule like;
- It is done by a process of evaluating activity sequences, durations, resource needs, and schedule constraints to generate the project schedule model.
- The schedule model is used to control the planned start and finish dates for project activities and major milestones based on the accuracy of the inputs. Schedule development can involve the extensive review and iterations in time and resource estimation for the right project schedule model can function as a baseline to track progress.
- Once we have defined start and end dates, it is recommended to share the detailed information with the project team to avoid any conflict in scheduling and availability of resources that might also be engaged in some other projects and thus ensuring it’s validity.
With the passage of time and work progress, the process of revision and project schedule maintenance continues and is essential to meet the project completion requirements throughout the duration of the project.
Critical Chain Method
The most vital advantage of this method is that by entering schedule activities, durations, resources, resource reliabilities, and logical relationships into the scheduling tool, it automatically creates the best possible schedule model with planned dates for concluding project activities.
As explained above, the critical chain method (CCM) is one of the key tools of schedule method with the help of which project team can include buffers in any project schedule path to accommodate any uncertainties and limitations of resources.
It is directly coming from the critical path method technique and considers the impacts of resource leveling, resource allocation, resource optimization, and activity duration uncertainty or imprecision on the critical path established using the critical path method.
For this, the critical chain method brings the concept of buffers and buffer management. There are three main types of buffers;
This type of buffer mainly takes into account any possible contingencies and is included between the final task and project finish date. Project delay or early finish will directly impact this buffer. The early finish will result in gain and any delay will result in a lesser buffer. The project will not be delayed from the original timeline as long as we have sufficient buffer available. It is recommended to only include 50% Approx. of the contingency of task estimate.
These types of buffers are included in the non-critical chain to avoid the effect of any possible delay of the non-critical chain on the critical chain. They are placed between the last task on a non-critical chain and the critical chain.
There is no difference in the calculation of feeding buffer and project buffer. As already explained above, the calculation is dependent on the safety excluded from the tasks on a non-critical chain.
Often considered less important compared to feeding and project buffers, these are kept as a reserve in the critical chain in order to avoid any delays in the time of need. It can be in the form of human resources or any machine etc.
This technique (CCM) measures the duration of activities without safety margins, logically build links, and availability of resources with statistically determined buffers composed of aggregated safety margins of activities at particular points on the project schedule path to bring in the effect of limited resources and project imprecisions.
The resource-oriented critical path is known as the critical chain. The critical chain method technique allows the inclusion of duration buffers which in other words can be described as non-work schedule activities to manage any unplanned event.
One buffer, included at the very end of the critical chain as shown below in figure is known as the project buffer and safeguards the target finish timeline from slippage along the critical chain.
Additional buffers, known as feeding buffers as already explained above, are included at every point where a chain of interlinked activities that are not on critical chain but somehow feeds into the critical chain.
Feeding buffers hence safeguard the critical chain from delays along the feeding chains. The size of every buffer should only take into account the imprecision in the timeline for the chain of the interlinked activities prior to that buffer.
Once we have finalized the buffer schedule activities, the planned activities are scheduled to their latest possible planned start and finish dates. Hence, instead of monitoring the total float of network paths, the critical chain method emphasizes on controlling the remaining buffer duration against the remaining duration of chains of activities.
The difference in Float & Buffer
So if you know something about float, you may be inclined towards considering it the same as a buffer. But in fact, they aren’t
Below are a few of the main differences between these two:
- By definition, a buffer can be described in three different categories: project buffer, feeding buffer and resource buffer whereas float is an entirely different thing and can either be total float or free float.
- By definition, a float is a difference between the length of the critical path and the non-critical path. A float will always have a zero value on the critical path.
- A buffer is more focused on inaccuracies and takes into account the contingencies. As already explained above, the project buffer is usually about 50% of the safety time that have not been considered in the activity estimate duration. It can never have zero value on a critical chain or any other chain.
- Float is entirely dependent on a critical path, whereas buffer is only relevant in the critical chain.
- Float is very simple to analyze. It has the same value for all the activities on a non-critical path, any activity can use it partially or fully, and other activities can use the remaining part.
Similarly, a buffer can also be utilized to accommodate the delay in any other activity. It’s up to the project manager how he/she wants to manage his/her project.
To summarize the discussion, there is always a chance of a problem occurs in the project execution phase. It’s always recommended to use the Critical chain method during the scheduling phase it addresses many things which we might not consider if we are only focusing on critical path methods such as resource availability, budget allocation, etc.