scope:

Description of Driving Event:

The nitrogen tetroxide (N2O4) vapor release, which occurred during a storage tank relief valve changeout, greatly exceeded the "one gallon quantity" specified in the task OMI V2197, sequence 03- 014. Also, sequence 03-074 states, "total amount of commodity involved: 1 gallon." Post incident calculations estimated the total release to have been 28 gallons. The vapor cloud of N2O4 far exceeded the 700-foot clear area called out in the OMI. Unless the magnitude of the release is accurately predicted, the downwind clear area cannot be properly established and personnel may be endangered.