UPDATE 2-Motiva Texas hydrogen unit shut after blast

(Updates with shut plant responsible for all refinery's hydrogen)

HOUSTON Dec 8 (Reuters) - A hydrogen plant operated by Praxair Inc (PX.N) at Motiva Enterprises's 285,000 barrel-per-day (bpd) Port Arthur, Texas, refinery was shut on Tuesday after an explosion and fire, according to a Praxair spokeswoman.

No injuries were reported among Praxair employees, said Susan Szita-Gore, company spokeswoman.

"I understand it was a pretty big bang," Szita-Gore said.

The Praxair plant supplies all of the hydrogen to Motiva refinery, Szita-Gore said.

No injuries were reported among Motiva employees following the malfunction, which was reported to Port Arthur police and fire departments.

Sources familiar with refinery operations said a hydrogen line ruptured on the unit.

Refiners have switched to having third-party providers produce hydrogen used in the refining of cheaper heavy, sour crude oils in motor fuels that meet strict U.S. environmental standards.

Motiva is a joint-venture between Saudi Refining and Shell Oil Co, the U.S. unit of Royal Dutch Shell Plc (RDSa.L). (Reporting by Erwin Seba and Kristen Hays)