A dropped keg caused a flash fire at the Rock Bottom Restaurant and Brewery on Friday morning, forcing an evacuation and tying up traffic in downtown Denver.

Denver Fire Capt. Craig Carter said chlorine dioxide, used to clean empty beer tanks, spilled Tuesday at the brewpub, 1001 16th St. It was mopped up and didn’t cause a problem until a worker dropped the keg Friday. A spark from the keg ignited remnant residue of the spill and fueled a flash fire, which released a plume of smoke.

Firefighters were concerned it might have been toxic, but tests showed no harmful toxics were released, Carter said. No one was injured. Police and firefighters shut down Curtis Street from 15th to 17th streets, but the free 16th Street Mall shuttle remained in operation. Kieran Nicholson, The Denver Post