A total of 27 storage units at Uncle Bob's Self Storage, in the 7500 block of Culebra, were damaged by fire Monday morning.
"Because of the fuel load, this is stuff that's going to burn and take a while for us to sort through, get completely out and for arson to go through," Deborah Foster, San Antonio Fire Department spokeswoman, said.
Some 45 firefighters and three arson investigators responded to the fire. Firefighters said there wasn't necessarily anything suspicious about the fire.
All of the doors to the storage units were closed and there was no one around whey they got there.
"We used our saw and opened up each of those aluminum doors to vent out the building," Foster said.
Opening the doors carried a risk for fire crews, who didn't know what was being stored in the building.
"For firefighters, every situation can be a scary situation, but when we are facing the unknown, that does make it more difficult," Foster said.
Foster said it would likely take arson investigators a while to figure out what sparked the flames because of all of the contents of the storage units.
"It's going to take arson a little while to sort through all the belongings and things like that to determine what the exact cause of this fire was," she said.