A technician accidentally loosened critical bolts holding a fitting to the top of an H2 tank, which caused a large hydrogen leak in the dewar. The fitting contained various instruments, and upon loosening the third bolt, H2 gas exited through an opening in the seal. The Viton or neoprene O-ring was blown out of its groove and was immediately frozen, making it impossible to reseal the fitting cover. The area was evacuated, the dewar was vented and the gasket was replaced. The ullage space was not purged with helium gas during the gasket replacement, which may have been responsible for small leaks which developed during the transfer.
The fitting containing the instruments was mounted on a flange, which was in turn secured to another flange. view more