The fire broke out in a detached garage in the 1100 block of N. Isabel Street just before 6:30 a.m. When firefighters arrived, the blaze was already fully involved.
Fire officials say there were some minor explosions because of ammunition, gas and camping fuels that were stored inside.
It took fire crews about 15 minutes to knock down the blaze.
One firefighter suffered second-degree burns, and another firefighter suffered a minor back injury.
A crew remained on scene to clean up the potential runoff from the flammable materials.