Taylor Swift -- Semi-Naked, Not Afraid During Fire Emergency (VIDEO)

7:45 AM PT -- We spoke to the venue ... the heavy pyrotechnics used at the end of Taylor's show triggered smoke detectors. Everyone had filed out and Taylor was backstage chilling in her dressing room when the fire alarm went off. No one was injured.

Taylor Swift's got nerves of steel ... even when she's barely clothed.

Fire alarms sounded backstage in the Houston stadium where she performed Wednesday night -- and even though everyone was urging her to get dressed and get out ... Taylor stood her ground, and recorded the moment for Instagram.

It turned out to be kinda funny since it was a false alarm.

The real fireworks came once T-Swizzle hit the stage for the first of her H-Town concerts with special guest Wiz Khalifa.