Traditional project management planning uses the critical path method where the emphasis is on the earliest finish date of the project and the critical path formed by the project activities.
This seems all well and good until you realize that critical path only you refers to time critical aspects of your project and does not consider other risk areas such as resource availability
But the real situation is worse than that.
Although tasks that are on the critical path have zero float which means that any delay to one or more of these tasks will place the same delay on the project finish date
So, what about the non-critical path tasks?
Well, these can be a problem as well since many will have small amounts of float making them candidates for end project delay even though they are designated as non-critical.
The approach to critical chain is to apply the buffers at key junctions of the network diagram
To in addition to this, the project buffer is also created
You may be thinking that all the above will lead to simply adding to the project time and cost and as such does not help in completing a project as early as possible
But there is a further step that must be considered and this is taken care of when carrying out estimating for each task
When seeking out realistic estimates individuals will tend to give a worst case estimate. There are many reasons for this – partly down to human nature. But the main reason is to reduce the risk of that estimate being wrong, and so padding it will decrease the likelihood of this happening.
The downside here is that when these tasks are connected into a network diagram it will usually result in a worst case extended project finish date, as well as bloated estimates for both work and cost
Critical chain overcomes this by using a best-case estimate for each task. What this means is, each task will have the duration and work effort based upon no snags, no delays, and experienced staff carrying out the specialist work
The next step is crucial and explains why the critical chain method is so powerful
A project buffer task is added at the end of the project, and this buffer contains a fractional ratio depending on various characteristics of the project. At a simple level, it may be that the buffer contains 25% of each task best case estimate.
As each task is completed then that ratio is subtracted from the project buffer to provide the latest estimated finish date
Buffers are also added at key junctions called feeding buffers, and estimated in a similar manner
In this way, the buffer is where the accumulated effects of all the uncertainties are dampened
The critical chain path will normally contain extra tasks over and above the critical tasks as it takes into consideration aspects such as resource constraints and thereby reduce is the possibility of resource contention
One of the powers of using critical chain is that it identifies dependencies between activities – either because of a constraint or a result of a common resource. In this way, the longest chain will be composed of sections that are schedule dependent and the sections that are resource dependent
To harness the full power of critical chain however, you need to be aware that there are over SEVEN different algorithms for determining Feeder and Project Buffers. Using these will depend on the characteristics of the project as each one will be unique.
A practicing project manager must master critical chain with the ability to tailor and apply it within their projects – to find out how, use this link to check out my Critical Chain Primer