Steps in the Critical Path Method

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To understand the impact of interrupting manufacturing operations for maintenance or upgrades, management must understand the sequence of events for shutdown and startup. Blindly "flipping off the switch" and then finding that steps in the process were overlooked can be disastrous. Diagramming the worst case scenario can lessen the impact on profitability and down time of equipment and operators. The Critical Path Method (CPM), developed by DuPont in 1957, gives a graphic view of a project, the time it will take and the sequence of activities to complete the project.

Things You'll Need

• Paper
• Computer
• Microsoft Excel

Identify and Organize the Components of the Project

List all activities needed to complete the project. Using a simple example of painting and recarpeting an office, some activities might be: pick out paint colors, remove furniture from the room, remove old carpeting, select carpeting, paint the room, fill and sand cracks and nail holes in the wall, etc. Making a complete list of all activities from start to finish will help you determine the scope of a project.

Determine which activities are sequential (must be completed before another activity) or concurrent (can be completed at the same time as another activity). Sequential activities will form the critical path, while concurrents will add to the time needed for completion. For the office renovation, removing the old carpeting, painting the walls and installing new flooring would be sequential activities. Selecting paint colors and a painting contractor are concurrent steps that would need to be completed before painting the walls.

Estimate the length of time for each activity. You can use past experience or tracking data to estimate completion time for each task. This does not take into consideration variations or other factors that can affect completion time, but is the best method at this stage.

Plot the Critical Path of Your Project

Draw the critical path diagram, using a simple circle and arrow figure, with a circle at both ends of an arrow. Put a number in the leading circle representing its place in the process. Label the circle at the end of the arrow with the next number in the sequence. As tasks are laid out in order of completion, the end circle of one task becomes the beginning circle of the next and takes its number as its start. The arrow itself is labeled with the task and estimated length of time for completion. Concurrent activities begin at the appropriate stage of the process and branch off, coming back at the stage when their completion is critical to the next step in the process.

Beginning with Activity 1, identify the longest route along the sequential activities from beginning to end. This now becomes the critical path for completion of the project Estimated project completion time is determined by totaling the time estimates for each activity.

Transfer the elements of the critical path diagram into an Excel spreadsheet. Enter the activities in sequence in the first column, with concurrent tasks as a subgroup for each sequential activity. In the next column, enter the time required to complete the task and in a third column, the estimated date of completion. Refer to the spreadsheet as the project progresses in real time.

Track the Project Using the Critical Path Diagram

Assign a project manager or team leader. As the project progresses, activities may need to be added or deleted. Changes in budgets, personnel and materials may all affect the critical path.

Update and modify the critical path diagram or spreadsheet as the project progresses in real time. Critical or secondary activities may arise due to changes from process improvement or system upgrades.

Apply the Critical Path Method to any process that has multiple activities, completion times and specific completion deadlines. It can be used to implement new processes, complete a renovation (as in the example) or reorganize office space. It may have been the brainchild of a chemical company, but it can be applied to any business or industry looking to improve productivity and effectiveness.

Tips & Warnings

• The Critical Path Method is most effective for established processes that don't have a lot of variation. For more complex processes, PERT charts or Gantt Charts can produce a better result.

References

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