Seven people died in an April 2010 explosion at the Tesoro oil refinery in Anacortes, Washington. A joint investigation by ABC News and the Center for Public Integrity found that aging refineries near major cities across America hold risks for local residents.

The state of Washington levied a record $2.4 million fine against Tesoro after the accident, saying it failed to check for cracks in the plant's aging equipment. A crack in a heat exchanger caused the explosion, according to the state.

A Washington state official said the deaths at the Tesoro refinery "could have been prevented and should have been prevented."

A fire and explosion at BP's refinery in Texas City, Texas, the third biggest in the U.S., killed 15 employees and injured 170 others.

The BP refinery was more than 70 years old at the time of the accident. In 2010, BP paid a $50.6 million fine to OSHA for safety violations revealed by the blast.

The chairman of the federal government's Chemical Safety Investigation Board, Rafael Moure-Eraso, says the industry mentality is to run the refineries until they break. "Basically what we're talking about is you are running this to failure," Moure-Eraso told ABC News. "The priority seems to be on production and safety seems to take a backseat."

In 1986, the U.S. government released a giant cloud of hydrofluoric acid in the Nevada desert to see what would happen if there were an unchecked release after an accident at a major oil refinery. Hydrofluoric acid is used in the gasoline refining process at 50 refineries in the U.S.

Dr. Ronald Koopman, a former government scientist, told ABC News that hydrofluoric acid is "nasty stuff" that can can destroy lung tissue and cause death by asphyxiation. The best course of action if you live near an oil refinery and there is an accidental release of hydrofluoric acid, said Koopman, is to stay inside and seal doors and windows. "If it's good and tight, and everything is closed, you can be protected for possibly the duration of the release," said Dr. Koopman.

Ironworker James Jamison was welding at the Sunoco refinery in Philadelphia in 2009 when an accident caused a hydrofluoric acid release. He told ABC News he became engulfed in a "rain cloud" of noxious gas. "The smell was so intense," said Jamison, "I could feel it through my eyes, my nose, it was like a heat wave came over me."

Jamison says the hydrofluoric acid release at the Philadelphia Sunoco refinery left him with permanent heart and lung damage.

Sunoco disputes Jamison's contention that the hydrofluoric accident left him with permanent heart and lung damage, and the two parties are now in court.

In a statement to ABC News, Sunoco said that since the accident at its Philadelphia refinery (shown here) it has invested $200 million in improving the safety and reliability of the equipment involved in the use and storage of hydrofluoric acid, "state-of-the-art technology" that it says will help avoid another accident.

Federal regulators urged new safety measures after an explosion and fire wracked the Citgo refinery in Corpus Christi, Texas on July 19, 2009.

The fire began with an explosion in the Citgo refinery's alkylation unit, which makes chemicals for high-octane gasoline. Hydrofluoric acid is used in refining premium gasoline.

Federal investigators said the accident at the Citgo refinery in Corpus Christi released a cloud of hydrofluoric acid In most places where refineries are running, the surrounding communities are unaware of the risks associated with hydrofluoric acid.

Residents of Corpus Christi say they hear warning sirens from the refinery at all times of the day and night. Citgo says it tests alarms daily, and encourages employees to sound the alarm if they think something has gone awry. "While this approach can result in false alarms, CITGO would rather sound the alarm and not need it, than not sound it if we need to," the company said in a statement.

Citgo said in a statement that the fire and gas leak at the Citgo refinery in Corpus Christi were contained, and never reached the surrounding community. A subsequent investigation by the U.S. Chemical Safety Board found that water systems meant to contain a leak didn't entirely succeed. On Feb. 24, the refinery agreed to pay $303,000 in fines to the state of Texas to setlle pollution violations related to the accident.

Janie Mumphord, who lives just a few blocks from the Citgo refinery in Corpus Christi, said she fears the worst. "You never know when you go to bed if you're gonna live through the night, or if you have to run through the night," she said.