CRASHING

The process of reducing the normal distribution of the project to a particular duration is called crashing

We know the critical activities control the project duration. Hence we've to reduce the duration of one or more critical activities so that the project duration time will be shortened. In other words crashing is done only on critical activities

For crashing the information that should be provided with are

• Normal cost of completing each activity
• crash cost of completing each activity
• crash duration
• indirect cost (if any)

Working rules

1. Draw the NWD & identify all the paths (don't calculate EST, LFT) select the critical path & identify its duration.
2. Name the critical path as parent critical path
3. for each activity. calculate cost slope using
   • Cost Slope = (Crash cost-Normal cost)/(normal duration-crash duration)
   • This cost slope indicates the additional cost incurred for reducing the duration of that activity for 1 day
4. (First crashing): Select the critical activity having least cost slope. Crash that activity to available period. IF parent critical path loses its status then crash that activity not to the full extent but possible extent, in order that the parent critical path should not lose its status.
5. After 1^st crashing verify parent critical path is still critical path. If a critical path exist the select the common activity for crashing. If there is no common activity, select one activity from each path having least cost slope & crash them simultaneously. Each & every time of crashing ensure that the parent critical path holds its status. At the same time other paths can also be critical in addition to parent critical path.
6. Crashing should be stopped if one of the following situations
   1. If all the activities in, at least one of the resulting critical paths are crashed then crashing is over
   2. If crashing cost exceeds the indirect cost then crashing should be stopped since crashing is not economical

Minimum duration:

The minimum duration of the project can be determined by quoting the crash duration of the activities lying in the paths. The path that takes the longest duration is called minimum duration of the project.

Optimal duration:

If indirect cost is given then only optimal duration can be decided. The duration at which crashing is not economical is called optimal duration. Optimal duration implies cost minimum & not duration.

The various cost involved in crashing

1. Project execution cost (PEC)

The sum of the normal cost of the activities is called project execution cost

1. Expected duration & associated cost

The critical path duration is called expected duration. The associated cost = PEC + indirect cost (if given)

1. Optimal duration & associated cost

The duration at/beyond which crashing is not economical is known as optimal duration. The associated costs are

PEC+  Indirect cost  upto optimal duration + crashing cost for reducing the duration from normal to optimal

1. Minimum duration & associated cost:

The duration of a project beyond which it cannot be reduced is called minimum duration. Associated costs are

PEC+ Indirect cost upto optimal duration + crashing cost for reducing the duration   from normal to minimum duration