A 17-mile stretch of Interstate 65 was closed while Hazmat crews cleaned up a chemical spill on Thursday.
Indiana State Police say a semi carrying 40,000 pounds of sodium hydrosulfite started leaking Thursday morning at a truck stop.
Some of the chemical mixed with rainwater and turned into a gas, creating a heavy fog.
Five people were hospitalized and complaining of breathing problems.
Sodium hydrosulfite is a flammable solid, which can ignite if it comes in contact with moisture.