Burglar bars at the Fiesta Dollar Super Store meant to keep out criminals also stopped firefighters from initially entering the business when it caught fire early Thursday.
San Antonio firefighters said heavy smoke poured out of the building in the 5100 block of South Flores when they arrived just before 12:30 a.m.
However, getting inside to tackle the flames was not an easy task, they said.
All of the windows and doors were covered with wrought iron security devices.
"(The business is) real tightly sealed up for the obvious reasons. They don't want any kind of burglary," said Jacob Mendiola, district chief for the San Antonio Fire Department. "The high security was a real problem, getting in. We had to access it from both the front and the rear."
Once they were able to enter the South Side business, firefighters put out the fire within 30 minutes.
Although arson investigators were called in, firefighters said the fire appeared to have started due to an electrical problem.
The fire caused an estimated $50,000 in damage, firefighters said.