CHULA VISTA, Calif. — A raging fire at a South Bay shoe store that left four firefighters injured — including one with severe burns — is now under investigation by a national team from the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Chula Vista Fire Department requested the special investigators, who arrived Thursday and began working to determine what caused the fire. They’ll work in tandem with local authorities and bring “state-of-the-art equipment” and other added resources to the existing investigation.

The blaze started at the Action Footwear retail store on H Street in Chula Vista last Monday evening. Four workers inside the store were able to escape unharmed, but blistering winds fanned the flames, the building’s roof collapsed, and crews dealt with a blown transformer and downed wires, all making the firefight particularly challenging.

Four firefighters were injured in the blaze, and while three were treated at the hospital and quickly released, a fourth remained at UC San Diego Medical Center for several days with second-degree burns.

In a news release Thursday, the City of Chula Vista explained that the decision to call in ATF’s National Response Team was made, “based upon the size of the building, the amount of fire damage, and the firefighter injuries.”

“The NRT provides an immediate and sustained nationwide response capability, deploying within 24 hours of notification, with state-of-the-art equipment and qualified ATF personnel,” the statement reads, in part.

“The NRT works in conjunction with other investigators to reconstruct the scene, identify the seat of the blast or origin of the fire and determine the cause of an incident. In the case of bombings and arsons, NRT members gather evidence to support criminal prosecutions.”

Authorities did not share further information on whether foul play was suspected in the shoe store case.