(CNN) — A massive explosion this week at a food dye factory in Louisville, Kentucky, left two people dead and a dozen others injured as smoke billowed out of torn metal structures and rubble.

Both victims were workers at the Givaudan Sense Colour plant, which produces colorings for food and drinks and is owned by Swiss manufacturer Givaudan.

For some Louisville residents, Tuesday’s blast revived memories of another deadly explosion at the same location 21 years ago, when it was under different ownership.

Here’s what you need to know.

What happened?

The explosion happened around 3 p.m. and was felt miles away in Jeffersonville, Indiana, according to CNN affiliate WLKY. It was extremely loud and blew out the windows of several nearby businesses.

Twelve people were injured and taken to the hospital, according to the mayor’s office. Only one was still hospitalized Wednesday evening, University of Louisville Hospital spokesperson Heather Fountaine told CNN.

It’s not yet clear what caused the explosion. Louisville authorities described it as a “large scale incident” involving hazardous materials, with federal agents assisting fire investigators.

“We don’t have any reason to believe at the moment that there was any type of nefarious activity,” said Shawn Morrow of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Givaudan is still “in the early stages of investigating the cause of this incident and … cooperating with first responders and supporting agencies,” it said in a statement.

Who were the two victims killed?

Two “team members” died in the explosion, Givaudan said.

They have not been publicly identified.

“We are grieving with the families, friends, and loved ones of those that were lost and injured during this very difficult time,” the company said.

One of the victims who died was found in the rubble hours after the company had said no employees were missing, Louisville Mayor Craig Greenberg said.

“We’d been told by the business that all employees were accounted for,” Greenberg said in a news conference. “Tragically, that was not the case.”

Givaudan blamed the confusion on “the extent of the explosion,” which forced them to send workers to two evacuation sites, its spokesperson told CNN late Wednesday.

“There was a miscommunication between the teams at the two locations when cross-referencing the staff list with those being transported to local hospitals. This initially led us to believe that all individuals were accounted for,” spokesperson Jeff Peppet said. “When it became clear this was not the case, we immediately coordinated with EMS at the site who re-initiated search and rescue operations.”

Is it safe now? What about nearby residents?

In the immediate aftermath, people within a 1-mile radius of the site were ordered to shelter in place as houses in the two blocks surrounding the plant were ordered to evacuate because their windows had been blown out.

By Tuesday afternoon, the shelter-in-place order was lifted – but the mayor still urged residents to be cautious.

“We’re dealing now with an unstable building that has partially collapsed and could collapse further,” said Louisville Fire Chief Brian O’Neill.

After using a drone to monitor air quality in the area, “we did not find any evidence of any release of anything hazardous,” he added.

Has this happened before?

The facility had a fatal explosion more than two decades ago under different ownership. The food coloring facility then belonged to D.D. Williamson & Company, which was acquired by Givaudan in 2021 and had its name changed to Givaudan Sense Colour.

On April 11, 2003, a “process vessel became over pressurized” at the D.D. Williamson plant, releasing 26,000 pounds of aqueous ammonia into the air and sending debris flying, according to a report from the US Chemical Safety and Hazard Investigation Board.

Authorities do not believe this week’s explosion involved the same material as the 2004 blast. “That dealt with a solid anhydrous ammonia that is no longer on site,” O’Neill, the fire chief, said.

The 2003 blast forced 26 residents to evacuate and 1,500 people to shelter in place. It also killed 44-year-old worker Louis Perry, for whose granddaughter the latest explosion brought up memories of the accident 21 years ago.

“You would think that after one explosion, it wouldn’t happen again. But here we are,” Lorrie Hibbard told CNN on Tuesday. “All I heard was that there was an explosion at the plant again, and it just takes you right back to 2003.”

The company was ultimately fined $10,000 by the Kentucky Labor Cabinet for that explosion, according to the Occupational Safety and Health Administration.

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