Workers at the TECO Big Bend power plant were trying to unplug a blocked tank when molten material poured onto them, killing two and injuring four others, officials said Friday.

Tampa Electric President and CEO Gordon Gillette said at a news conference that the incident happened Thursday at a coal-fired boiler, while workers were performing routine maintenance on the slag tank at the plant. 

Slag is a byproduct created when coal is burned for electricity.

Gillette said workers were trying to clear a blockage when hot slag came rushing out onto them - some closer to the tank than others. The hot slag, which spewed out like lava from a volcano at about 1,000 degrees covered the floor six inches deep and about 40 feet across were the workers were, according to reports. 

Contractor Christopher Irvin, 40, was killed along with a 60-year-old TECO worker. The longtime TECO employee who died is not being identified at this time due to a request from the family. 

The four men who suffered life-threatening injuries have been identified as Gary Marine Jr., 32, Antonio Navarrete, 21, Frank Lee Jones, 55, and Armando J Perez, 56. 

"Because of the significant radius, all of those on scene were affected in some way, unfortunately," he said.

Victims sustained burns as well as other injuries that "would be categorized as very severe," fire-rescue officials said.

Gillette also spoke about the longtime TECO worker who was killed.

"He worked at TECO for decades," Gillette said. "In fact, he was going to be celebrating his 35th work anniversary with TECO. He worked at TECO as a senior plant operator, he was well respected, and well liked by all of his fellow team members."

On Friday, two investigators from the federal Occupational Safety and Health Administration were arrived at the plant to begin an investigation. 

Information from the Associated Press was used in this report.

Union challenges use of contractors to increase profits

IBEW Local 108, the local chapter of the International Brotherhood of Electrical Workers, issued the following statement regarding the accident at Big Bend Power Station on June 29, 2017.

"IBEW Local 108 expresses our sincere condolences to the families of those who have lost their lives in this tragic accident. The local hopes that those that were injured have a full and speedy recovery.

This incident could have been avoided - period. It's time to listen to the employees. It's time to stop using contractors to do “routine maintenance” when the safety of this maintenance has been questioned by employees. It's time to stop putting profit before safety. It's time to truly put safety first.

IBEW Local 108 has always  been concerned and focused on employee safety. We are currently working with OSHA in their investigation, and we are determined to do all that we can to prevent this from happening again. This will take cooperation, understanding, and effort from all parties. It can't be one sided."

Previous accidents

The incident occurred at the Big Bend Station, one of three TECO power plants and the largest. It runs on coal.

Thursday's incident comes almost two decades after a deadly explosion at TECO's Gannon power plant. That happened on April 8, 1999, with three people killed and 50 more injured.

Hydrogen contained inside the 375-megawatt generator exploded when the access cover was prematurely opened during a maintenance outage, Tampa Electric said the next day.

TECO was fined $25,200.

In July 2014, a contractor died when he slipped and fell while working at the plant. He fell through a grate on a catwalk.