Union criticizes largest US refinery's safety record

* Exxon says lost time incidents down 70 percent

* Worker recovering after being burned by steam

HOUSTON, June 16 (Reuters) - The United Steelworkers union on Thursday criticized the safety record of the largest U.S. refinery, two days after a worker was burned by steam while working at Exxon Mobil Corp's (XOM.N) 560,640 barrel-per-day (bpd) Baytown, Texas, refinery.

USW International Vice President Gary Beevers said in a statement that Tuesday's injury was the latest in a string of 33 process safety incidents including leaks and flaring at the Baytown refinery.

"These 33 occurrences prove there are far too many process safety incidents at this refinery," Beevers said. "Since the Baytown facility is the nation's largest refinery, it should lead the way in process safety."

An Exxon spokeswoman said safety was a core value for the company that has in place systems to continuously improve safe operations at its refineries.

"Since 2000, Exxon's Americas Refining workforce has reduced the total number of lost time incidents by about 70 percent," said company spokeswoman Kristen Hellmer in a statement.

Glenn Oviedo was burned over 25 percent of his body while operating a steam vent valve on a refinery's coking unit Tuesday.

Oviedo was flown by helicopter to a Houston hospital and is expected to recover, Beevers said. (Reporting by Erwin Seba; Editing by Lisa Shumaker)