According to some work within the nuclear industry there are four times as many latent errors/conditions that exist within a system leading to an event than active errors.  And these latent errors remain undiscovered and hidden until an event occurs.  Further, in all the scenarios and events studied the latent conditions contributed most often to the event and caused the greatest increase in plant risk.  Latent, or hidden, conditions or errors remain so until a problem occurs and then they are easy to see and spot as part of the post event investigation.  Thus the key is to detect these latent errors sooner and through active surveillance and monitoring means to eliminate them from potentially causing harm.

What are some of the errors or conditions that might exist within an operation that goes undetected until a problem occurs?  Well, the list is long and too large to be captured here, but some  examples include:

• Missing bull plugs in piping systems.
• Car-sealed valves left in the wrong orientation.
• PSV, piping, pressure vessel inspections not completed, completed poorly or inaccurately.
• Critical device defeats left in place for excessive durations / forgotten.
• Mislabeled switchgear / electrical cables / equipment.
• Missing, incomplete, not up to date training or certifications.
• Incomplete maintenance, but yet noted as complete.
• Incident review recommendations or engineeering recommendations forgotten and not implemented.
• Unsafe working conditions allowed to continue to exist.

A key lesson learned from this study is that from a systems-thinking perspective we must design surveillance, monitoring, and detection systems that constantly search for these latent conditions.  Audits and assessments of key work processes and conditons are cirtical activities that mustn’t be shunned but embraced as they help to understand the effectiveness of the work programs and highlight potential gaps that can then be fixed and closed.  Supervisors, managers and leaders of organizatiosn are also critical components in the process as they should be constantly on the look-out for potential gaps, and latent conditions in the work and operations.  And workers themselves have a particularly important role to play in identifiying potential latent conditions and ensuring that they do not create and leave error-traps fro others as they complete their work.

It is surely a frustrating experience for anyone who has reviewed the findings of an incident investigation to find that there were conditions, or traps, leading up to the incident that existed for days, weeks, or even years before, that if they only had been identified sooner, and closed, a serious incident could have been prevented.  This is the work of everyone associated withthe operations - the constant vigilance to search for and eleminate these latent conditions.  It may be difficult work, it may even be unrewarding work, but it is defintely critical work and it is what safety is all about.