Late last week, U.S. Chemical Safety Board (CSB) provided an
update
on the agency’s investigation into a March 5, 2012, release of hydrofluoric
acid (HF) at the CITGO refinery in Corpus Christi, TX. CSB team lead Johnnie
Banks provided the update. Banks stressed that although no injuries resulted
from this incident, “CSB takes any accident involving the release of HF very
seriously” due to its highly corrosive and toxic nature.
According to investigators, the leak resulted from failure
of the seal on a 12-in. flange on a process vessel in the alkylation unit. Leaks
at that flange had been reported since September 2011, and maintenance had been
performed on several occasions. More than 3 weeks prior to the incident, a new clamp
to enclose the leak was ordered. “The unit was not shut down,” Banks said. “Rather
the clamp was ordered in hopes that its installment would stop the leak.”
On the day of the incident, process liquids containing
hydrocarbons and about 5% HF were released in a steady stream which worsened
through the late afternoon. CSB has determined that the incident resulted in
the release of 300 to 500 lb of HF.
The release was eventually detected by sensors that
triggered the alkylation unit’s automatic water cannons, which are designed to
capture airborne HF. These water cannons are intended as the last line of
defense in the event of a release of HF. However, CSB learned that the water
cannons were activated on two days following the incident—planned work
activities during which the company expected that the cannons might be
triggered. CSB reported its concern over the facility’s apparent reliance on
the water cannons to “control” an HF release during maintenance activities.
CSB says it will examine commonalities between this incident
and a 2009
incident at the same facility, in which approximately 21 tons of HF released
from alkylation unit piping and equipment, resulting from an intense
hydrocarbon flash fire that critically injured one employee and exposed
another to HF.