A Dallas gun range caught on fire on Sunday after a patron reportedly fired military-style tracer rounds inside the building.

A spokesperson for Dallas Fire-Rescue said that the tracer rounds, which ignite like a flare to make projectiles visible to the naked eye, were against DFW Gun Range rules. The rounds apparently hit the back wall of the building, resulting in the four-alarm fire.

By the time firefighters arrived, popping sounds could be heard inside the building as ammunition exploded. At least 50 people were in the building at the time and were able to escape unharmed. One firefighter, however, was injured by smoke inhalation.

"It was pretty scary," a range patron named Brett told KVUE. "There are a bunch of bullets in there, and there's not telling how far or when they're going to go off."

By nightfall, the fire was under control and authorities turned their attention to securing weapons in the building -- including assault rifles -- from possible looters.

Authorities also said that they were concerned about the possibility that lead from melted bullets could contaminate ground water, but the results from initial tests were not available by Monday morning.

No charges were expected because police considered the tracer rounds an accident. The patron could face a civil suit for damages, including destruction of the roof and one wall of the building.

Watch this video from KVUE, broadcast Feb. 25, 2013.