Two men were injured by a flash fire Wednesday while they were conducting maintenance work on a sewer line.

The incident occurred in the 3800 block of Amnicola Highway around 9:00 am. Chattanooga firefighters were dispatched to a "confined space explosion."

Captain Robert Thompson with the CFD's Special Operations division said when the flash fire broke out, the men were down in a manhole. They both were able to escape and call 911 for help.

The fire was already out when firefighters arrived. 

One of the men was transported to a local hospital. A spokesperson for the fire department said he appeared to have second-degree burns. The other man suffered minor burns and declined to be transported. 

The cause of the flash fire is under investigation. 

"Representatives with the Tennessee Occupational Safety and Health Administration (TOSHA) will also be conducting an investigation of the incident," the spokesperson added.

The two men worked for SpectraShield, a subcontractor used by the City of Chattanooga.