A team of investigators has determined that a release of toxic gas at a CITGO refinery in Corpus Christi, Texas last week occurred during a leak from a piping flange.

Chemical Safety Board (CSB) investigators are looking into the March 5 incident. in which highly toxic hydrofluoric acid (HF) was released from the refinery’s alkylation unit.
 
Investigators are currently conducting follow up interviews with plant personnel and further examine the unit.
 
To date the team has determined that the incident occurred during a leak from a piping flange on a 12-inch line operating at 145 pounds per square inch gauge (psig). The released process stream contained hydrocarbons and about 5% HF, according to refinery officials. The release triggered the alkylation unit’s automatic water cannons, designed to capture airborne HF.
 
Last week the CSB designed and conducted a test on the failed flange intended to determine the leak rate. The line was pressured up with nitrogen gas and the rate of depressurization measured. CSB investigators are currently calculating the estimated size of the release using the test data. Investigators will also be examining several failed bolts that were recovered from the flange, reviewing key data from the process control system, and examining records of previous releases of HF from the flange and other locations in the alkylation unit.