The accident led to a temporary shutdown of a caustic neutralization unit and affected other plant operations, Petron refinery vice president Alfred Trio said in a statement. Petron operates the country’s largest refinery.
Four refinery workers were treated for "minor injuries" but none required hospitalization, company spokesman Rafael Ledesma said.
The four were identified as Zander Diaz, 27; Hector Quicho, 23; Angelito San Pedro, 31; and Ernesto Pencil, 42.
Trio described the incident as an "operational upset" that "would not interrupt our product supply."
The affected units are now back in operation, he added.
The caustic neutralization unit, built in 1993, reportedly separates phenol and naphtenic acids used in the production of gasoline and diesel fuel. — Raffy Viray