Oak Ridge staff prepared a work package to change out the filter locking mechanisms in the Y-12 Uranium Chip Oxidation Facility (UCOF) HEPA Exhaust Unit #1. The first phase of the job was to remove a number of bolts in the filter plenum and remove the old licking mechanisms. The work site (the filter plenum) is normally accessed by reaching in. Job planners visited the site for inspection, but the job was not planned until several months later. Some of the planners did not revisit the site before preparing the package. Some planners believed the plenum was too small for a worker to actually enter, while other planners thought that an entry was physically possible, but not permitted. This was not fully discussed and resolved. The plenum was initially classified as a "Confined Space" per 10 CFR 1910.146, but was later downgraded to an "Enclosed Space" since the package assumed the space was too small for a worker to enter and workers would reach in and do the work without entering bodily.

The job started with a briefing, opening the job and radiation work permits, and establishing safe conditions. The plenum air was sampled for oxygen and explosive gasses, an air sampler for radioactive material was set up, and workers wore tyvek suits and full-face respirators. Maintenance workers began removing bolts closest to the door. The workers partially entered the exhaust unit to remove the bolts. Some of the bolts could not be easily reached and one of the maintenance workers completely entered the HEPA unit and stood up in the exhaust duct plenum to remove the remaining bolts. The other worker never fully entered the unit. Once the worker entered the HEPA unit exhaust duct plenum, the Safety Technician questioned the supervisor about entry into a confined space. Reference to a written communication discussing the evaluation of the HEPA exhaust unit as an enclosed space was presented and work continued.

The HEPA filter locking mechanism replacement job was planned in two phases. Phase I was to be the removal of the existing bolts that had held the old filter locking mechanisms. Phase II was to be the installation of the new bolts and new filter locking mechanisms.

In three separate meetings, that included maintenance personnel and planning team members, the Activity Hazard Analysis, job scope, and work package were reviewed. Limitations centered mostly on the welding activities, (Phase II). Although a restriction on full body entry into the exhaust unit was discussed during planning meetings, the workers did not clearly understand this restriction applied to all phases of the work and believed that the designation of the space as an enclosed space allowed full entry.

The root cause of this event has been attributed to Inattention to Detail during the job planning for the work. Neither the work package nor the Activity Hazard Analysis included necessary written information to prevent bodily entrance into the HEPA exhaust duct plenum. The hazards of each activity were analyzed and clearly marked with written control measures. Since this phase of the work (Phase I) was considered low hazard, no independent instructions were given to maintenance personnel for entry into the HEPA chamber. Nor were instructions such as a restriction for full body entry into the exhaust duct plenum given.

Job planning personnel should be reminded of the need to base job planning on a current field review of the work site.

Activity Hazard Analyses and Work Packages should clearly specify confined space requirements and provide sufficient details such as work restraints and limitations.

Maintenance supervisors and planners should be trained on proper work package preparation and stop work authority when work is being performed outside the bounds of a work plan.

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