FRANKLIN, Tenn. (WKRN) — An explosion at a Franklin middle school was likely sparked by a leaking propane tank, officials said. 

It happened at Poplar Grove Middle School around 7:15 Tuesday morning.

Franklin fire officials are still investigating, but say they do have some idea of what took place.

“It’s a little nerve wrecking,” said Capt. Joseph Hill of the Franklin Fire Department. 

The explosion occurred as parents lined up in front of the school for drop-off.

“So, there was a lot of traffic,” said Capt. Hill. “We were able to get into the school, and once we were able to pull into the parking lot, it was a construction area.”

Hill said the school building is being expanded and the explosion happened inside a construction container holding various items for construction crews.

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A preliminary investigation shows a propane tank was the likely cause. Captain Hill said a construction worker plugged an extension cord into an electric heater inside this container just moments before the blast.

“There was an actual propane tank in there that was hooked to a propane grill,” Hill explained. “What they are thinking is — it hasn’t been determined completely yet — that there was a small leak of some sort from the propane tank and it filled up the box and when he started the electric heater, it caused an explosion.”

Thankfully, no one was injured. School went on as scheduled.