Hidden Incident Causes

Hidden Incident Causes

The Purloined Letter

Finding hidden incident causes is an important part of incident investigation.

In the year 1844 Edgar Allan Poe published the short story The Purloined Letter set in the city of Paris. In the story the bad guy - Minister D - has in his possession a letter that contains compromising information about an unnamed lady. He is using this information to blackmail her. In order to find the letter the Prefect of police and his men have searched Minister D's residence in great detail, even using a magnifying glass to examine the tables and chairs. But they have found nothing. 

Dupin purloined letter incident investigation
Dupin taking the purloined letter

So they bring in an amateur detective, C. Auguste Dupin. He quickly finds the letter - it is hidden in plain view on a card rack in D's room.This classic story, written so many years ago, provides lessons for process safety professionals who are conducting an Incident Investigation. 

No Suprises

After a serious incident occurs those charged with running the investigation often find that the causes of that incident to have already been described and thought about. In our book Process Risk and Reliability Management we write,

If you want to know the cause of an incident, look in the filing cabinet; chances are that someone described it before the event actually took place. 

In other words it is very possible that someone had already identified the potential for the incident during an audit or hazards analysis or some other evaluation program. For example, in the case of the Piper Alpha catastrophe reports had been written about the potential for a massive fire from a ruptured riser, which turned out to be a major factor in the disaster. Yet those reports were ignored.

"Purloined letters" on process facilities can be hidden in many places, including the following:

  • Audits
  • Process hazards analyses
  • Maintenance reports
  • Inspection reports
  • Prestartup safety reviews

Of course, the best time to find these letters is before an incident takes place so that management can take the appropriate corrective action.


Further information on this topic can be found in the book Process Risk and Reliability Management and the ebook Incident Investigation and Root Cause Analysis.