On a given day personnel were removing a blind hub that had been used to temporarily isolate a portion of a gaseous hydrogen system. As a result of a sudden release of 2,800 psig gaseous nitrogen, sand and debris kicked up from the concrete pad and caused minor injury to two technicians.

During the investigation, it was found that:

The temporary configuration change to the gaseous hydrogen system was initiated on multiple work orders and by different individuals. There was no single document that documented the temporary system configuration.
The procedure for performing the work was written using a drawing that had not been updated to show the actual system configuration. Verbal field direction was given when it was discovered the system was not configured per the work order.
Incorrect clamp removal techniques were used. Upon pressure release, the clamp, blind hub, and seal ring became projectiles that had the potential to cause significant personnel injury.

Incident Date
Jun 29, 1999
  • Hand Tools
  • Construction Tools
Damage and Injuries
When Incident Discovered
Lessons Learned

Work documentation (work orders and baseline drawings) should reflect the current system configuration.


Develop procedures for temporary change configuration control of high-pressure systems. The overall work process should be included in one work authorization document.
Re-emphasis to all personnel that current procedures be followed. If the work order is not written to reflect the current system configuration, stop work, revise work order, and have the work order properly reviewed prior to continuing work.
Write a procedure for proper clamp removal and installation and train technicians to the procedure.