Putnam County Chief Deputy Coroner Dave Brown identified the victim as George F. Leggett, 65, Columbus, Ohio.
Following a Tuesday morning autopsy in Terre Haute, Brown ruled the death accidental due to blunt force trauma.
What caused the wreck, though remains unknown.
"No medical cause for the crash was found during the autopsy and a possible theory is Mr. Leggett may have fallen asleep at the wheel," Indiana State Police Sgt. Joe Watts said.
Drug and alcohol test results will not be available for up to two weeks, but Watts said there are no early indications of impairment.
Indiana State Police and Putnam County emergency agencies responded to the overturned tractor-trailer just east of the 30-mile marker at 4:26 p.m. Monday.
They found the driver dead at the scene and the tanker trailer broken nearly in half, spilling approximately 6,000 gallons of what State Police are identifying as a "highly flammable hazardous industrial solvent."
Radio dispatches on Monday evening indicated the liquid to be acetone.
The truck was registered to Quality Carriers of Florida.
The westbound vehicle left the roadway for an unknown reason and struck a cement bridge support near County Road 775 West.
Hazardous materials responders from the Cloverdale Township and Greencastle fire departments were dispatched to the incident. Cleanup continued Tuesday with haz mat crews from Indianapolis and New Albany.
The westbound lanes were opened at approximately 5:20 a.m. Tuesday, followed by the eastbound lanes at approximately 6:30 a.m.
Traffic was diverted to U.S. 40 via U.S. 231 at Cloverdale, State Road 243 at Putnamville and State Road 59 at Brazil.
Additional cleanup efforts began around 10 a.m. with some lane restrictions and slowed traffic expected near the 30-mile marker.
Some motorists were evacuated after their vehicles became stuck in the median while attempting to make U-turns. No other evacuations have occurred or are anticipated.