At around 4 a.m. in a cooking oil refining and packaging plant, refined oil was found leaking from a tank and part of the spilt oil had entered the rainwater network. The oil had leaked out of the manhole at the top of the tank. The level detector and the alarm transmission system were operating correctly; it was the lack of monitoring that resulted in the overflow. Some of the oil released from the tank landed on the top part of the retention basin wall, making its way outside the plant. However, a large portion of the spilt oil flowed to the facility’s internal purification plant. The rainwater network was cleaned over the following 6 days. Stainless steel deflector panels were installed on all the tanks located on the property limit.