(AP Photo/Ross D. Franklin)

The walls were on fire at Phoenix International Raceway.

No it wasn't the heat in the Valley of the Sun, nor the racing.

The walls were literally on fire, thanks to an exploding brake rotor.

Two fires broke out late in Sunday's race when the brake rotors on Chris Buescher's No. 37 car broke off and flew into the gap in PIR's SAFER barrier.

The pieces wedged between the barriers and the styrofoam inside caught fire, sending plumes of black smoke into the air.

The race was red flagged and track safety officials were able to put the fires out relatively quickly.