More than 3,000 people across 50 city blocks were evacuated. More than 800 people went to the hospital suffering from respiratory problems.
At 5:20 p.m., a crane lifting a 40-ton heater convection unit dropped it, severing a 3-inch pipe connected to an acid tank.
Hydrogen fluoride gas spewed from the rupture and formed a cloud over the city.
Marathon workers eventually drained the tank of acid.
More than 30 people were admitted into the hospital with hundreds more treated for respiratory problems and eye irritation.