UPDATE 2-Fire erupts at Mexico's biggest oil refinery, some hurt

(Updates details on injured, previous Pemex accidents)

MEXICO CITY, Nov 24 (Reuters) - A fire broke out at Mexico’s biggest oil refinery on Tuesday and some staff were evacuated, a spokesman for state-run oil company Pemex said, the latest in a string of incidents to hit the company’s refineries.

The Red Cross said nine people were injured, while Pemex said eight people suffered minor injuries and were being treated.

A Pemex spokesman said the fire had been controlled and that the refinery, which supplies fuel for the domestic market, was operating normally except for an alkylation unit. The refinery has the capacity to process 330,000 barrels per day.

Photographs taken by emergency services workers showed a blazing fireball and a thick black plume of smoke rising up into the sky from the facility located in the city of Salina Cruz in the southern state of Oaxaca.

Luis Velazquez, a civil protection agency official in Oaxaca, said that nearby schools had been evacuated and that local hospitals were on red alert to treat any injured.

“This is a highly populated zone,” he said.

Pemex said last week it had reduced its annual accident rate last year by more than 33 percent. However, a Reuters investigation earlier this year found that Pemex was reducing its accident rate by including hours worked by office staff in its calculations.

The key international indicator for measuring worker safety is the so-called lost time injury frequency (LTIF). Pemex says its LTIF decreased by about 88 percent in 2014 from 2013, falling from 3.14 to 0.37 injuries and fatalities per million man hours, according to data released in July by the International Association of Oil and Gas producers (IOGP).

That rate fell markedly because Pemex reported an additional 330 million man hours worked in 2014 - an almost seven-fold increase from the year earlier - even as its production decreased for the tenth year in a row.

There have been a series of fires at Pemex installations including refineries and oil platforms this year alone, which come as Mexico seeks to lure private investors to revive its flagging oil industry.

Accidents have plagued Pemex for years. In 2013, at least 37 people were killed by a blast at Pemex’s Mexico City headquarters, and another 26 people died in a fire at a Pemex natural gas facility in northern Mexico in September 2012. (With additional reporting by Lizbeth Diaz and Elinor Comlay. Editing by Michael O’Boyle, Simon Gardner, David Gregorio and Diane Craft)