A massive piece of debris that flew from the Givaudan Color Sense plant after an explosion is pictured on Wednesday, Nov. 13, 2024 in Louisville, Ky. (Dylan Lovan / Associated Press)For years, neighbors who lived near a factory in Louisville, Kentucky, complained amongst themselves and to local officials about a variety of strange smells coming from the plant, which produces colorings for food and drinks.Some described it as an ammonia-like smell, while others said it was more like burnt sugar or burnt caramel. They worried a bit about living so close to the plant, but never expected what happened Tuesday, when an explosion killed two workers, and blew out windows and ripped pieces off the roofs of nearby homes..“I’ve always thought about it, like this is unsafe — seems like — because there was always huge steam coming from the place at night. But I never really thought that this would happen," said Shelby Dix, 31, who lives in an apartment in a multifamily home that is separated from the plant property by an alley.The explosion injured 11 other employees at Givaudan Sense Colour, and caused a partial collapse of the building. Three remained hospitalized Wednesday.“We are grieving with the families, friends, and loved ones of those that were lost and injured during this very difficult time,” the Swiss-based company said in a statement.Amanda Strecker, who lived in a townhouse near the plant from 2018 to 2022, said she had long been concerned about the ammonia-like smell.“We felt when we lived there that something was going to happen. It was just a matter of time,” she said. “We’ve had a lot of problems with chemical smells in the air, reporting it locally to the environmental office, and them coming out and not finding anything.”During the first few years Strecker lived in the neighborhood, the plant was owned by D.D. Williamson & Co. Givaudan acquired the plant in 2021.“I had the plant manager’s number at one point and I would call and let them know, ‘Hey, something’s not right.’ They’ve had a lot of issues there,” Strecker said.In April 2003, while the plant was owned by D.D. Williamson, a tank exploded and killed a worker. Federal investigators determined the tank exploded because it was missing its pressure relief valve, which had been removed when it was moved to the Louisville plant in 1989.In 2009, D.D. Williamson paid a total of $600,000 in civil fines to the U.S. Department of Justice and the Louisville Metro Air Pollution Control District to resolve allegations of Clean Water Act violations at the Louisville plant.Officials said they have not yet determined what caused the explosion Tuesday. Louisville Fire Chief Brian O'Neill said the building housed hazardous chemicals — typical for factories of that kind — and firefighters did not immediately know if any had been compromised. He said monitoring of air and runoff found none.Louisville Mayor Craig Greenberg said employees initially told officials “everything was normal activity when the explosion occurred.”“This is an incredibly sad and tragic incident,” Greenberg said. “I want the families of the two victims to know that the hearts of all Louisvillians are with them."As of February 2021, the factory made caramel colorings for the food industry by heating sugar and water and adding chemicals such as aqueous ammonia for some products, according to permitting documents filed with the Louisville Metro Air Pollution Control District.At the time of the permits, the plant was still owned by D.D. Williamson & Co., which was founded in 1865 and initially supplied malt to brewing companies, later developed colors for soft drinks and more recently produced natural colors for food and beverage companies.The Swiss flavor and fragrance company Givaudan acquired D.D. Williamson in 2021. Givaudan Sense Colour offers a range of “natural colours, caramel colours, burnt sugars, and fruit and vegetable-based browns” for the beverage market, according to its website. Spokespersons for Givaudan did not immediately respond to emailed requests for comment Wednesday.Last year, the air pollution control district cited the plant for failing to notify the district about unspecified excessive emissions. It also was cited for not submitting annual compliance certifications and reports in a timely manner, as well as not abiding by permit requirements concerning monitoring, recording and inspections. The company agreed to pay a $7,500 fine.Carly Johnson, her husband and their 4-year-old son were at home when they heard a “crazy loud boom,” felt their house shake and heard things falling off the walls and shelves as if a bomb went off.During the 12 years the family has lived about a block from the plant, they've smelled what Johnson described as a “weird, burnt sugar smell.” She and her husband had worried about living so close to the plant, knowing about the explosion two decades ago. But she said she thought that since it there had already been such a traumatic event there, "they would have done everything they could to prevent this from happening again.”“Windows and everything can be replaced. I’m just mad about my son going through that. That’s what makes me the most mad,” she said.The Louisville Fire Department is leading the investigation with help from state and federal partners. A reconstruction team from the Bureau of Alcohol, Tobacco, Firearms and Explosives was headed to Louisville to help determine the cause of the explosion. Givaudan said in an earlier statement that it is cooperating with authorities.