Implementing buffer management
Step Five

Implementing buffer management
Using buffers in Project management
 
 

 A buffer is essentially a form of protection against variation and a control over the performance of the system.

We have decided to manage our system through the constraint. Our system remains, however, a network of interrelated processes. These are all affected by variation. This variation will inevitably affect the performance of the constraint and therefore the Throughput of the system.
We can protect the constraint’s performance by implementing buffer management.

The unit of measurement of the buffer is time. How much time do we need to complete something? How many finished goods should be ready by a certain time?  The buffer  protects the constraint from the variation of the processes that feed it and that could “starve” it. So we establish the length of the buffer on the basis of the variation of the processes which impact it. The greater the variability of the process, the longer the buffer, and vice versa.

In order to identify problems and initiate actions to overcome them, we can divide the buffer into three zones. When we find a disruption to the flow of a process in zone 3, we do not need to interfere. In zone 2 we begin to take notice, and in zone 1 we must take action at all costs to protect Throughput.

Using buffers in Project management

A project is a set of interdependent activities that have to be completed respecting certain requirements.
Just like  an organization, a project is a system. This means we can apply the Five Focusing Steps we saw in Step Four to managing a project. The major obstacle to completing projects successfully is the variation in the interdependent processes involved. Unless we have made our system stable, with control mechanisms in place,  we cannot apply the Five Focusing Steps:

1)  Identify the constraint: the constraint of a project is the longest chain of dependent events (not only in a temporal sense but also considering the use of common resources) on which the duration of the project depends. We call this the Critical Chain.

2) We exploit the Critical Chain by protecting the total time of the project with the  project buffer. This protects the project conclusion date from fluctuations along the Critical Chain. The size of the buffer depends on the variation of the interdependent processes. The resource buffer guarantees that the resources we have allocated along the Critical Chain are present when needed.

3) We subordinate everything to the Critical Chain schedule. This means that all ‘feeding’ activities (the non-critical parts of the project) are completed before the planned start of the critical activity. We guarantee this by installing feeding buffers.

4) We elevate the Critical Chain when the total duration of the project planned is too long and unacceptable for the customer.

5) We go back to Focusing Step 1. In project management this means moving from planning to execution. By using buffer management, project managers can anticipate problems and so ensure the project runs smoothly.
But they have to go further than this. Their job is to change people’s attitude to completing tasks. Projects have to be run like rally races; the winning team passes the baton  on to the next runner as soon as possible. Otherwise you will have a new constraint to tackle -  inertia.
 

Buffer management is the control mechanism that can protect the constraint and indicate areas of the system that are not in control.  To get the maximum out of buffer management , we must make sure that all the main processes  impacting the constraint are stable, with an interval of variability that allows them to be managed.

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Tony Rizzo' s site: Theory of Constraints and Product Development