NASHVILLE, Tenn. -- Medical statistics obtained by the Channel 4 I-Team show about 69 current Nashville firefighters are battling cancer, and a leading researcher wonders if the firefighters' exposure to diesel fumes may be to blame.

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For the first time, the Nashville Fire Department released medical information that shows in the past 20 years, 30 Nashville firefighters have died from cancer.

Dr. James Lockey of the University of Cincinnati is a leading researcher into cancer rates and firefighters and told the I-Team the number of firefighters with cancer and who have died from cancer is concerning.

"It's serious enough that I think it should be paid attention to," Lockey said.

Part of Lockey's research focuses on toxins in diesel fumes that may have caused firefighters to contract cancer. In Nashville, firefighters were exposed to diesel fumes from fire trucks idling in fire halls for decades before researchers linked the fumes to cancer rates.

"We know we have been exposed to it. And we continue to be concerned about it," said Nashville Fire Chief Stephen Halford.

The 69 firefighters make up about 8.6 percent of the entire fire department. Researchers could not say if that number is high, given that there have been no conclusive nationwide studies conducted among firefighters with cancer.

Cancer Support Group Recently Formed For Firefighters

Veteran District Chief Bobby Connelly said he never thought about how the diesel fumes swirling around him for decades may have caused his prostate cancer.

When the I-Team decided to invited all Nashville firefighters with prostate cancer to gather for a support group, 17 other firefighters showed up.

"Recently, we've had a rash of people, firefighters, being diagnosed with prostate cancer," Connelly said.

Lockey's research indicates concern that firefighters are especially prone to prostate cancer if exposed repeatedly to diesel fumes.

"Diesel exhaust is a known cancer-causing agent," Lockey said.

Firefighters Unprotected for Decades

A single large fan was placed into each of Nashville's fire halls in 1990 as a way to suck out the diesel fumes.

But Halford said those fans may have been ineffective, because they were put on times that only ran three minutes and they were manual, so firefighters had to remember to turn them on their way to fire scenes.

Fire chiefs said those fans weren't as effective as hoses that attaches to the trucks and sucked out the fumes.

Halford said he immediately noted the problem when he took over the department in 2001.

"I wasn't satisfied that there was adequate ventilation systems to remove the harmful products of diesel emissions fuels," Halford said.

In order to protect future firefighters, Halford instructed in 2002 that all trucks be equipped with filters that remove diesel fumes. But, he said, those filters don't do anything for the firefighters who have been exposed to fumes for decades.

"Most of the firefighters have been here a long time, so they have accumulated the effects of the carcinogens," Halford said. "I think not just in Nashville but all over the nation fire chiefs are concerned about what the older generation of firefighters have been exposed to."

Connelly does not blame the Nashville Fire Department for his cancer; he said his disease may just come with the territory.

"I just don't. It's my job. It would be like a guy going to work in a coal mine, that the odds of him getting lung cancer are pretty great. But he's going to do it anyway," Connelly said.