Risk Assessment: Tools, Techniques, and Their Applications

14.7 Examples of Fault Tree Analysis

14.7.1 Simple Example

The following examples show the fundamentals of FTA. We start with analyzing a simple cooling system flushing procedure. This procedure can also be analyzed using human reliability analysis (HRA) techniques, but we use FTA at this point. The procedure reads as follows:

Warning: cooling system must be below 100°F before draining.

1. Begin with the engine cold and ignition off.

2. Remove the radiator pressure cap.

Warning: ethylene glycol coolant is toxic and must be disposed of in an appropriate manner.

3. Open the petcock at the bottom of the radiator and drain the coolant into a bucket.

4. Close the petcock and fill the radiator with water.

5. Start the engine and turn the heater control to hot. Add cooling system cleaner and idle the engine for 30 min (or as per the instructions on container).

Warning: cooling system must be below 100°F before draining.

6. Stop the engine and allow it to cool for 5 min. Drain the system.

7. Close the petcock, fill the radiator with water, and let the engine idle for 5 min.

8. Open petcock and drain the water.

9. Repeat steps 6–8.

10. Close the petcock.

11. Fill cooling system with 50 : 50 mixture of water/nontoxic antifreeze/coolant.

The first step will be to determine the credible top events. In this case, it will be as follows:

Mechanic is burned.

Cooling flushing failed.

In fact, the “mechanic is burned” top event can be grouped under the “cooling flushing failed” ...