HOUSTON (Reuters) - One contract worker remained hospitalized on Saturday after a hydrofluoric acid leak at Phillips 66's Ferndale, Washington, refinery on Friday, the company said in a statement.

Five other contract workers and one Phillips 66 employee were released from the hospital by early Saturday after being treated for exposure to hydrofluoric acid, which can be fatal.

The workers were exposed while the 101,000 barrel per day (bpd) refinery had units shut down for an overhaul that began on Wednesday.

The leak was from the refinery's alkylation unit according to a report on the Bellingham Herald newspaper website.

Alkylation units use hydrofluoric acid to convert refining byproducts into octane-boosting components of gasoline.

The hydrofluoric acid release forced workers at the refinery to shelter indoors for about an hour, the company said.

Alkylation units are considered the most dangerous in a refinery because a release of hydrofluoric acid from an explosion or fire could spread a possibly lethal vapor cloud across surrounding communities.

The South Coast Air Quality Management District, which regulates polluters in the Los Angeles area, has proposed banning the substance. A 2015 explosion at a Los Angeles-area then owned by Exxon Mobil Corp was found to have nearly released hydrofluoric acid into the atmosphere.

A Nov. 22 explosion at an alkylation unit injured four people at Exxon's refinery in Baton Rouge, Louisiana.





(Reporting by Erwin Seba; Editing by Bill Trott and Mary Milliken)