Incident investigation workshop

BUILDING THE “WHY” TREE

• BUILDING THE “WHY” TREE
• Step 5. Verify the hypotheses as true or not.

• VERIFICATION IS IMPORTANT
• Must verify each hypothesis through:
• Testing - oil analysis, motor dynamics
• Measuring - vibration, ultrasonic, infrared
• Observing - high speed photography, video cameras
• Experimenting - statistical analysis
• SHERLOCK HOLMES:
• "When you have eliminated the impossible, whatever else remains, however unlikely, must be true.

• Use the above form to keep track of how you verify your hypotheses
• File the form with the Why Tree for future reference

• RCFA VERIFICATION OF HYPOTHESIS

BUILDING THE WHY TREE

• BUILDING THE WHY TREE

• Motor controller was removed from service and the blown fuse was found when being repaired in the shop.
• In the shop, the circuit was found to be drawing the ' proper current. The blown fuse was verified to be a 35 amp fuse. The function required a 50 amp fuse.

• A Fuse opened

• Physical Cause of Failure

• 35 & 50 Amp Same Size and Apperance

• 35 & 50 A Fuses mixed in same bin in store

• Electrician did not read label

• Electrical thought 35A was required

• 35 & 50 A Fuses mixed in same bin in store

• Could not be verified because evidence was missing

• System Key Factors

• System Key Factors

• System Key
• Factors

• AND

• 35 & 50 A Fuses mixed in same bin in store

• Electrician did not read label

• Could not be verified because evidence was missing

• System Key Factors

• Human Key
• Factors

• System Key Factors

• Physical Key Factor

• No Other Plausible sources