Fire crews were dispatched to a store within West Towne just after 11 a.m. to investigate an odor compared to “rotten eggs,” Fire Department spokeswoman Cynthia Schuster said in a statement.

Upon entering the mall, firefighters detected carbon monoxide at levels greater than 20 ppm, along with the strong odor that was originally reported, prompting the department’s Hazardous Incident Team to be called in, Schuster said.

Crews traced the odor to a mobile floor scrubbing machine that uses a rechargeable battery. The charging system was overcharging the battery, causing the battery to off-gas, and though the scrubber was stored in a separate area from the mall’s shopping areas, the gasses drifted in, Schuster said.

The mall opened at 12:30 p.m., after firefighters ventilated the building and confirmed with air monitors that the space was safe to occupy, the mall opened at 12:30 p.m., Schuster said.

From State Journal archives: 'The most exciting thing that's ever happened to shopping in Madison': 24-page special section marked the opening of West Towne Mall in 1970