A sulphur dioxide leak at Port of Tampa forced people indoors for about an hour Thursday.
The air warning included downtown Tampa, Channelside and Harbor Island.
Tampa Fire Rescue said they were alerted to the situation by a 911 call from someone on Harbour Island, who reported seeing a plume of smoke coming from the port.
Investigators say a crew doing routine maintenance on a sulphur tank at Gulf Sulphur sparked a small fire inside the tank. As crews used steam to knock the fire down, it mixed with the sulphur, causing sulphur dioxide to be released from the tank.
Crews adjusted water streams so they sprayed in a fog-mist pattern, which officials said was part of an attempt to create a "blanket" to help dissipate the cloud. Officials said it took about two and a half hours to control the fire.
"They've been using a mist from the fire truck lines over these tanks to try to help break up the cloud and help dissipate it," Capt. Lonnie Bennefield said.
The air warning did not significantly impact businesses near downtown Tampa.
Hooters General Manager Robert Fisher says he kept his staff and customers inside until the Port Authority lifted the warning.
"It's just the nature of the beast in being in an area that has as much business and commercial traffic as we have," Fisher said.
Tampa fire investigators say they are not aware of any violations at the Gulf Sulphur facility at Port of Tampa.
No one was injured during the incident.