Tina Partridge wasn't expecting to see her dad at the door. He was working a contract job at a Tampa power plant, but made the drive to Jacksonville to surprise his grandsons.

"The boys were thrilled," Partridge recalled.

She thought nothing of saying goodbye to him that night in 1999. He had spent his whole career in power plants, and long assured her the work was safe.

But days later, a giant fireball shot through Tampa Electric's Gannon Power Station in Hillsborough County, hurling heavy sections of the wall into the parking lot. Her father, Johnny Bass Sr., was killed at 52.

Over the last two decades, more workers have died at Tampa Electric's power plants than at those run by any other Florida utility, the Tampa Bay Times has found.

No other utility had more than three deaths, including much larger companies like Florida Power & Light and Duke Energy. Tampa Electric had nine.

That includes the four workers who died after an accident June 29 at the Big Bend Power Station in Apollo Beach. Senior plant operator Michael McCort and contract workers Christopher Irvin, Antonio Navarrete and Frank Lee Jones suffered severe burns when a molten substance called slag gushed out of a tank.

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To put that accident in context, Times reporters pored through news stories and analyzed tens of thousands of OSHA inspections to identify 19 fatalities at Florida power plants since 1997.

Tampa Electric makes up nearly half, although it covers less than 10 percent of households in the state.

In searching the records, the Times also learned that on May 24, five weeks before the most recent accident, four Big Bend workers were sent to the hospital because anhydrous ammonia was released at the plant. The pungent gas can cause death by suffocation.

Power plants are generally safe, especially compared to other industrial operations, experts say. There are some hazards, including dangerous liquids and high-pressure steam. But on average, workers are more likely to get hurt in a factory or a construction site, federal data shows.

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Tampa Electric says its internal statistics show a steady decrease in incidents over the past 20 years, and that it takes the safety of its team members and contractors "very seriously."

"Safety is the No. 1 priority at Tampa Electric," the company said in a statement.

But two power plant safety experts interviewed by the Times said nine deaths in 20 years is unusual.

Lee Marchessault, who spent nearly four decades in the electric industry including as a power plant operator and runs the consulting firm Workplace Safety Solutions, said it could signal deeper problems.

"If I was in charge of safety for that organization, I would be looking into possible root causes of the incidents: management, lack of training, lack of maintenance," he said. "This is a huge red flag."

• • •

At fossil-fuel power stations, the safety of the workers is the responsibility of the company running the plant. There's little oversight.

Like other employers, electric utilities must report a death or serious injury to OSHA, the federal agency that regulates workplace safety. But with just 2,200 inspectors, OSHA can't thoroughly monitor the nation's 8 million work sites.

[Luis Santana | Times]

The Big Bend Power Station in Apollo Beach was the site of a fatal accident last week.

"OSHA is not going to come in unless there's some major catastrophic event or someone makes a complaint," said Scott Ray, president of Premier Safety Partners, a firm that develops safety management programs for businesses in the energy sector.

OSHA does not publish a list of power-plant deaths and accidents. The agency posts some details from its inspections online, but those can be difficult to find, particularly if a contractor is involved.

To tally the number of power-plant deaths in Florida, Times reporters compiled a list of every power plant in Florida, then searched OSHA's database of accidents and inspections by each plant's name and address. They also searched news stories from across the state, looking for accidents, injuries and fatalities involving both employees and contract workers.

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The Times did not include deaths unrelated to power plant operations, including two for Tampa Electric: Joseph Bell, a contractor who died when his commercial riding mower flipped at Big Bend in 2008, and a security guard who lost control of his Chevrolet Blazer and plunged into a cooling pond at the Polk Station plant in 1997.

The newspaper also left out two deaths that happened at plants run by other utilities. One involved the construction of a new plant. The other involved a vehicle accident at a waste-to-fuel facility.

Still, the total for Tampa Electric was higher than for the next five utilities combined. Duke Energy had three deaths. Pinellas County Utilities had two. Florida Power & Light had one.

• • •

Tampa Electric plants had safety problems long before the 1999 explosion that killed Bass and two co-workers and injured about 50 others.

In 1985, a maintenance worker died in an accidental fall.

[Times files (1999)]

Hillsborough County firefighters sweep through Gannon Station after the explosion in 1999, looking for workers.

Four workers were rushed to the hospital in 1997, when hot slag spewed from a tank at the Gannon plant. Two suffered second-degree burns.

A chemical known as Fyrquel leaked for nearly a week at Big Bend in March of 1999, veteran electrician Scott Mishler told reporters. Mishler said he suffered brain damage and memory loss, and lost feeling in his feet. He was one of seven workers who sued in 2002. Tampa Electric said the lawsuit was without merit. It was dismissed in 2015.

RELATED: Year after acquiring TECO Energy, Emera faces crisis management in worker deaths

Leandris Drew started picking up shifts at Gannon through a temp agency in early 1999 for $5.87 an hour. He didn't think shoveling coal and sweeping floors was particularly risky, he said. He remembers a sign on the wall saying the plant had gone some 300 days without an accident.

"It was easy," he said. "I would just shovel it and dump it."

Arthur Fedor, who had been working maintenance at Gannon for two years at that point, saw it differently. He called the job "dangerous" and routinely watched his co-workers get into "stupid accidents," he said.

[Times files (1999)]

Arthur Fedor, a maintenance worker in Tampa Electric's Gannon Station Power Plant, speaks to reporters in 1999 after being injured in an explosion at the plant. CREDIT: Times Files (1999)

Both men were working on the day of the 1999 explosion. Drew was approaching the boiler. The blast threw him to the ground and melted his clothes to his skin. He spent the next three months in the hospital.

Drew never held a steady job again, he said. To this day, his left wrist bends inward.

Fedor was hurt, too. When he opened his eyes in the helicopter on the way to the hospital, he thought he was back in Vietnam. The doctors said he had nerve damage. He retired shortly thereafter.

Within two days, Tampa Electric blamed the accident on worker error. But six months later, OSHA determined the company was at fault and issued $25,200 in fines — the maximum allowed, an agency official said.

RELATED: Trigaux: Amid Tampa Electric workplace tragedy, a reminder too many Floridians die at work

After that, Tampa Electric installed new safety managers at each of its plants, said Vonia Walther, who was hired to oversee safety at the Polk Station plant. The company also enhanced its contractor training program, she said.

"The results speak for themselves," said Walther, who left in 2014 and now lives in North Carolina.

But in 2006, an accident claimed the life of another worker. Vernon Ostrander, a 52-year-old contract painter from Fort Myers, had been tasked with refinishing a 6,900-pound water box at Big Bend. He noticed the structure starting to tip over and tried to run, according to an OSHA inspection and a medical examiner's report. It fell and crushed him.

Yet another contractor, 31-year-old Bryan Hagan, died in 2014. Hagan, who lived in Polk County, slipped through a grate on a catwalk at the Bayside Power Station, which replaced Gannon.

• • •

Last week's accident at the Big Bend plant has brought renewed attention to Tampa Electric's safety record. The six men involved were trying to unplug a slag tank using pressure washers — a common method, according to experts.

Two survivors remain in the hospital.

Tampa Electric and OSHA have released few details about the accident. Both are still investigating.

[Luis Santana | Times]

Tampa Electric spokeswoman Cherie Jacobs speaks at a press conference outside the Big Bend Power Plant last week.

The union for workers at the plant suggested the incident was a sign of a larger safety issue. In a statement, business manager Doug Bowden called on Tampa Electric to "stop using contractors to do 'routine maintenance' when the safety of this maintenance has been questioned by employees."

RELATED: Deadly accident thrusts quiet utility Tampa Electric into the limelight

His pointed message to the company: "It's time to stop putting profit before safety."

Neither Bowden nor union president Steven Fountain returned calls from the Times.

In light of the incident, Tampa Electric leaders have said that workers "at all levels" of the Big Bend Power Station must take more than a dozen online safety classes, each concluding with an exam.

Tampa Electric has a new parent company as of last year, the Nova Scotia-based utility Emera. Its leaders are working on a new companywide standardized contractor safety program.

But Ray, of the consulting group Premier Safety Partners, said Tampa Electric's history merits a deep review. The deaths, he said, are "an indicator that there could be cultural and budget and resource constraints."

Hilda Ramirez, whose brother Antonio Navarrete was among those who died, said she would favor more immediate action.

"They should just close that plant," she said.

Editor's note: This story was updated July 8 to reflect the death of Frank Lee Jones in Tampa Electric's June 29 accident at Big Bend.

Tampa Bay Times staff writers Adam Playford and Anastasia Dawson and researcher Caryn Baird contributed to this report. Contact Kathleen McGrory at kmcgrory@tampabay.com or (727) 893-8330. Follow @kmcgrory.