LOS ANGELES (CBSLA) — Federal investigators arrived in Los Angeles Monday to help arson teams figure out what caused a Saturday explosion that sent firefighters racing down a ladder through an inferno, their jackets and helmets burning.

In total, 12 firefighters with the Los Angeles Fire Department were taken to local hospitals with various injuries. And on Monday, only four remained hospitalized, though their road to recovery would likely be long and hard.

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“Surgeries, skin grafting, fighting infection and you also don’t see the mental scars that our members go through,” Capt. Erik Scott said.

Scott said that from the time crews arrived to the explosion was only eight minutes.

“When you see it begin, it is a light smoke that’s happening and it only took eight minutes for it to turn into a blowtorch inferno,” he said. “We want to know why.”

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And back at the scene, a national response team of agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Los Angeles Police Department and LAFD was working to figure that out, the charred ladder still in place outside the building in the 300 block of East Boyd Street.

“We are going to comb through every aspect of that building, determine what is inside, how much is inside and what had happened,” Scott said.

Authorities have since identified the business as Smoke Tokes and said they believe there was butane inside. An investigation into the business found that it lacked a commercial license for the location and was warned by the Food and Drug Administration for misbranding required nicotine warning labels on its products.

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And just as the investigation gets underway, families of the firefighters are also beginning to grieve the reality of what happened, including one family that visited the scene of the explosion in an attempt to process the trauma experienced by their loved one.