scope:

Description of Driving Event:

A cover plate bolted to the top of a high pressure helium filter was blown off and the contents of the filter (pyrex wool and silica gel) were expelled. The resulting failure occurred because there were only three bolts holding the cover in place instead of the sixteen bolts required to fill all the bolt holes. The filter was pressurized to 1700 pounds per square inch with helium when the pneumatic explosion occurred.

Preceeding the accident, as part of a maintenance program, the filter cover was removed for cleaning and reactivation. The bolts were frozen and difficult to remove. After three bolts were removed, the balance of them were cut off. When the cover was reinstalled, the three good bolts were put on but other bolts were not available to complete the bolt hole circle. Without knowledge of the incomplete assembly, the system was pressurized by the test crew resulting in the pneumatic explosion.