Question

What do you think about adding a project buffer for the entire project, as critical chain scheduling suggests?

What are some ethical considerations when using slack and buffers?

Answer 1

The Critical Chain/Buffer Management (CC/BM) approach aims at the construction of latest start schedules where the project activities use aggressive time estimates and puts a clear focus on the determination of a realistic project deadline. In order to keep the probability high that the project deadline will be met, the CC/BM approach protects the project duration and the critical chain of the project using various buffers. This buffered scheduling approach is the topic of this article and is discussed along the following dimensions:

• Project buffer: A unique and single buffer to protect the project deadline
• Feeding buffer: Multiple buffers to protect parts of the critical chain
• Resource buffer: Multiple artificial buffers that act as warning signals to assure the availability of resources

A single project buffer is added at the end of the project network between the last activity and the project deadline. Any delays on the critical chain will partly consume this buffer without having an effect on the project completion date. Consequently, a project buffer acts as a protection of the project completion date which might be variable due to changes in activity durations on the critical chain. Its size should depend on the expected changes and variability of the activities on the critical chain. Figure 2 displays the unique project buffer at the end of the project displays a project network with 8 activities and a latest start schedule with a project duration of 12 time units. The numbers above each node in the network are used to refer to the aggressive activity duration estimate (see ”Aggressive activity time estimates: protecting against activity delays”) while the label below the node refers to a renewable resource that is required to perform the activity. The renewable resources A, B, C, D and F have an availability of one, while the renewable resource E availability is restricted to two units. The construction of the resource feasible latest start schedule is discussed in ”Critical Chain/Buffer Management: (Dis-)advantages of scheduling projects as-late-as-possible”.

Project practitioners “do not engage in or condone behavior that is designed to deceive others, including but not limited to, making misleading or false statements, stating half-truths, providing information out of context or withholding information that, if known, would render our statements misleading or incomplete.”The intentional modification of project or supplier integrated master schedules (IMS), or scheduling inputs or outputs, in a manner designed to mislead stakeholders, hide factual information, win the job or contract, mask performance problems, inflate margin, buy time to fix problems without executive leadership involvement, or other similar goals.

• Preferential Sequencing: structuring IMS logic to favor one stakeholder’s position or interests over another’s • Duration Padding: adding an artificial time buffer “just in case” • Duration Compression: arbitrarily reducing durations to offset the impact of late or slipping predecessor tasks • Hiding Slack: using constraints, lags, improper logic or inflated durations to mask slack • Abusing Project Logic: intentionally manipulating dependencies to mask schedule issues or potential problems • Excluding Scope from the IMS: intentionally not including tasks in the IMS to show an artificially early project completion