UPDATE 2-Fire hits Venezuela's Petropiar oil upgrader

* No injures at 180,000 bpd facility

* Second incident at Petropiar this month

By Marianna Parraga

CARACAS, Oct 25 (Reuters) - A small explosion and fire hit Venezuela's Petropiar heavy oil upgrader on Tuesday in the second incident at the 180,000 barrel per day (bpd) facility this month, but no one was hurt, officials said.

Petropiar is a joint venture between state oil company PDVSA and U.S. oil company Chevron . Venezuela's four upgraders convert tar-like crude from the OPEC nation's Orinoco belt into lighter, more valuable oil.

A source at the plant told Reuters the facility had been stopped by the small blast that struck a diluting tank at about 6:45 am, but that there were no injuries.

PDVSA confirmed the incident, but said the upgrader was still functioning while a contingency plan was put in place.

"It was not a serious accident. We had a situation in one of the diluting tanks that collapsed part of the roof of the unit and produced a white cloud," Eulogio del Pino, PDVSA's vice president of exploration and production, told Reuters.

He confirmed that no one had been hurt, and said operations at the unit had been slowed down for evaluation. He said there would be no impact on production.

"PDVSA reports that the upgrader has not stopped working and is continuing its activities while a contingency plan is put in place," the company said in a separate statement.

Petropiar had restarted on Oct. 13 after being shut down for two days following an equipment failure.

The South American country's upgraders and network of refineries have been plagued by operational problems and accidents since 2009, leading to a fall in export volumes.

A second PDVSA-run upgrader, the 130,000 bpd Petroanzoategui, is offline until next month for planned maintenance. Venezuela's four upgraders have a combined capacity of 620,000 bpd.