HOUSTON Aug 7 The U.S. Chemical Safety Board said on Friday four investigators would go to Exxon Mobil Corp's (XOM.N) Joliet, Illinois, refinery to probe a hydrofluoric acid release that critically injured a worker on Thursday.
An Exxon spokesman said the company had no comment about the CSB's decision.
"Investigations into the cause of the accident are ongoing," said Exxon spokesman Kevin Allexon.
A propane leak at about 12:30 p.m. CDT (1730 GMT) Thursday on an alkylation unit at the 238,600 barrel per day (bpd) Joliet refinery led to the hydrofluoric acid release.
Four investigators currently probing a July 19 alkylation unit fire at Citgo Petroleum Corp's Corpus Christi, Texas, refinery, which also released hydrofluoric acid, will examine the Joliet refinery event, said board spokesman Daniel Horowitz.
"There's a general concern that there have been a number of these alkylation unit accidents," Horowitz said. "Any time hydrofluoric acid is released, it's a cause for concern."