Officials are investigating the cause of an early-morning fire Monday outside a tire shop in South St. Paul.

Mark Erickson, assistant fire chief of the South Metro Fire Department, which serves West St. Paul and South St. Paul, said the fire started in a semitrailer filled with tires that was parked outside Pomp’s Tire Service, 575 Hardman Av.

It took about 30 firefighters and three engines about an hour and a half to extinguish the blaze, which was reported by a passerby just before 4 a.m., Erickson said. The Inver Grove Heights Fire Department also responded to the call.

The fire destroyed the trailer, which was used to store old tires destined for a recycling plant, said John Norling, an employee of the shop.

Tire fires can be particularly tricky to contain, Erickson said.

“They’re made with a lot of petroleum products, so they burn very hot, and so until you can get them to cool down or stop the chemical reaction as they’re burning, it takes a lot to” to extinguish, he said, “especially with the large volume that we had.”

Libor Jany