The document provides an overview of the Critical Chain/Buffer Management (CC/BM) project scheduling approach. It discusses six key steps: 1) using aggressive activity estimates, 2) constructing an as-late-as-possible schedule, 3) identifying the critical chain, 4) determining buffer positions, 5) determining buffer sizes, and 6) inserting buffers into the schedule. The approach aims to protect the project deadline by introducing buffers at different positions, including a project buffer, feeding buffers, and resource buffers.

1. Andrei Dragota
An I master TI

2. The Critical Chain/Buffer Management (CC/BM)
approach originally introduced by E. Goldratt in his novel
“Critical Chain”, written in 1997 as an application of the
“Theory of Constraints”, is a project management
technique that introduces some novel ideas on top of the
well-known and generally accepted resource-constrained
project scheduling principles. It introduces the idea of
buffering projects, rather than individual activities, in a
clever way in order to guarantee that the project deadline is
met, and can therefore be considered as a new approach to
assure better project control through project and feeding
buffer management.

3. This presentation gives an overview of the Critical
Chain/Buffer Management (CC/BM) approach of project
scheduling and will be briefly explained along the
following six steps:
o Step 1. Come up with aggressive estimates
o Step 2. Construct an ALAP schedule
o Step 3. Identify the critical chain
o Step 4. Determine appropriate buffer positions
o Step 5. Determine appropriate buffer sizes
o Step 6. Insert buffers into the schedule

4. Based on the general idea that the protection of the
project deadline is the primary goal rather than the
protection of each individual project activity, the activity
durations should be set to an aggressive estimate to avoid
that the work of an activity is smoothed out over a longer
duration than really necessary. Goldratt mentions three
main reasons why project activity durations often are
smoothed out over longer durations, as follows:
o Murphy’s law: If something can go wrong, it will
o Student syndrome: Wait until urgency
o Parkinson’s law: Work expands to fill the allotted time
Aggressive time estimates refer to time estimates where
the probability of exceedance is relatively large, e.g. the
50% percentile.

5. In contrast to the commonly used earliest start
scheduling approach mostly used in traditional project
management and scheduling , it is suggested to schedule
each project activity as-late-as-possible nearby its
predefined project deadline. This latest start schedule is
quite risky since it makes every project activity part of the
critical path which might put, in combination with the
aggressive activity time estimates, the project deadline into
danger.

6. Similar to the critical path concept that distinguishes
between critical and non-critical activities, a resource-
feasible project schedule has a so-called critical chain
defined as the longest chain in the project that determines
the total project duration. The main difference with the
critical path concept is that it takes the limited availability
of renewable resources into account.

7. The new idea of the CC/BM technique lies in the clever
positioning of buffers to protect the project deadline
through the use of three types of buffers. Each buffer has a
specific goal and needs to be positioned at the right place to
protect the right part of the project data, as follows:
o Project buffer: A unique and single buffer to protect the
project deadline
o Feeding buffer: Multiple buffers to protect parts of the
critical chain
o Resource buffer: Multiple artificial buffers that act as
warning signals to assure the availability of resources

8. Sizing buffers as a way to put safety time in the project is
a crucial step of the CC/BM approach. Both the project and
all the feeding buffers need to be sized appropriately to be
able to act as buffers against delay. Although Goldratt
initially proposed to use the simple 50% rule (i.e. the size of
the buffers is equal to 50% of the duration of the project
activities it should protect), a more clever way should be
used that sizes buffers according to the risk of the activities
it should protect.

9. Inserting buffers into the project schedule creates a
buffered project baseline schedule that can act as a tool to
measure performance and provides dashboards (i.e. the
buffers) that need to be monitored to trigger corrective
actions.