On August 13, 1978, at 5:30 a.m., there was an accidental release of gas, primarily isobutene, at the East Chicago Terminal. The release occurred as a tank battery was being filled via pipeline. A liquid level gauge malfunctioned, and the tanks were filled liquid full. This caused a relief valve to activate, releasing the gas to the atmosphere. A line to another tank battery was opened, the pressure was equalized and the relief valve closed. The gas released was composed of approximately 70& isobutene (CAS Registry Number 75-28-5) and approximately 30% isopentane (CAS Registry Number 78-78-4). Each component was considered 95% pure. The maximum estimate of the amount released is 250 barrels. Local police and fire officials were notified, and residents in the area of the release were evacuated. Three houses in the area were destroyed and twelve others were slightly damaged by fire, but the exact cause (or causes) has (have) not been determined.