Investigating Investigation Methodologies

Ambiguous Description
Handout For IRIA2003 Presentation

Ludwig Benner Jr
Williamsburg VA 9/18/03


(Note: presentation handout content was reformatted to improve viewing with browser.)

Examples of ambiguous description in CSB report, disclosed by MES

(? is placeholder for missing data element)

  • ? told lead operator extruder had been run with purge material
  • ? scheduled restart for March 12
  • ? raised extruder temperature to 315†C
  • ? decided to close PCT without level detector
  • ? called Maintenance ? to assist with extruder problem
  • ? decided to divert process flow from PCT to RKP
  • ? observed small fire in extruder and what did they see
  • ? ignited residual purging material ?
  • ? ? did what about fire in extruder
  • ? observed vapor leak from RKP cover and what did they see
  • ? left instructions for night shift to empty PCT and RKP of polymer
  • ? purged extruder with purge material to clean screws
  • ? extinguished remaining fire
  • ? decided to not do recommended HAZOP after drawings finalized
  • ? designated HAZOPS team for safety analyses of facility
  • ? designated HAZOPS methodology for facility safety analysis
  • ? observed thermal degradation in product performance tests
  • ? tested unsuccessful alternative PCT level indicators
  • ? isolated hot oil system to stop flow from tubing break
  • ? recognized PCT was too small after overfilling
  • ? repaired PCT relief valve fouled with polymer
  • ? repaired PCT relief valve fouled with polymer (2nd time)
  • ? repaired PCT relief valve fouled with polymer (third time)
  • ? ignited hot oil vapor cloud
  • ? submitted engineering request to redesign system
  • ? shut down Amodel unit to repair equipment in extruder
  • ? mechanical problem delayed startup of unit for 4 ? hours

Examples of questions raised by MES

  • Why didn't solvent clean out ash in extruder?
  • Timing of fire/solvent shutoff/fire out?
  • Was hot oil involved with PCT pressure rise?
  • Why did workers have to position themselves in harms way to remove the head?
  • Why did Maintenance Tech remove bolts in sequence he did, and would another sequence have changed the outcome?
  • Need to confirm that hot oil continued flowing to heat inlet line to PCT after shutdown
  • before and after head blew off - did that contribute to heading of contents?
  • Why didn't HAZOP recommendation successfully control hazard? (Methodological problem)
  • Why wasn't unsuccessful recommendation remedied when experience showed it was unsuccessful? (system problem)
  • Why did Operators position selves with Maintenance Technician at head of PCT (if they did)
  • What exactly created internal pressure -what were roles of hot oil, overfilling, and decomposition of stored material in PCT
  • What ignited fire in extruder? Why did it spread
  • Who told whom what and why about pre-run?
  • What was data and rationale for this decision? Who made it?
  • Find out what procedure is to learn from incidents ‚system breakdown or people problem?
  • Find out why air could get into the extruder, providing oxygen for fire??
  • What was the impact trauma that killed 2 workers - tank cover or plastic from inside tank?