Four Pemex workers were hospitalized after sustaining injuries in an incident at a refinery in the state of Hidalgo on Monday afternoon.

Media outlets initially reported that there had been an explosion at the state-owned oil company’s Miguel Hidalgo Refinery, near the city of Tula, but Pemex told the Hidalgo government that wasn’t the case.

In a statement, the Hidalgo government said it was informed that there was a “spontaneous release of high-pressure stream from an automatic valve” in the refinery’s diesel hydrodesulfurization plant

Workers were checking the valve when it suddenly opened, “releasing high-pressure steam onto the turbine, which broke and flung pieces of metal,” according to the statement.

Four workers were apparently hit by the metal shards. They were taken to hospital to receive treatment for non-life-threatening injuries, the Hidalgo government said. Four other workers sustained minor injuries that didn’t require treatment in hospital, according to reports.

Pemex employees said on social media that the situation at the refinery was brought under control, but the company itself has not publicly commented on the incident.

Later on Monday, a second incident occurred at the Tula refinery. Municipal Civil Protection authorities reported an explosion at around 6:35 p.m. in the refinery’s waste hydrodesulfurization plant.

They said that the explosion — whose cause was not specified — did not pose a risk to the general population. Authorities said they weren’t aware of any injuries.

As of early Tuesday afternoon, Pemex hadn’t commented publicly on that incident either.

The Tula facility is the company’s second largest refinery. Pemex — which has debt in excess of US $100 billion and received billions of dollars in tax relief this week after its credit rating was downgraded by Moody’s last Friday — operates seven refineries in Mexico, including the new Olmeca Refinery on the Tabasco coast, as well as one in Texas.

With reports from Milenio, Excélsior, AM and El Universal