Was i fired unjustly?

I work in a Pharmaceutical Plant in Illinois (Morton Grove), as a Filler/operator. Occasionally, i'm igned to work in the pumphouse area where they blow air into the line when the big tanks are empty. I was not trained to work back there and the senior supervisor knew this. On the 20th of june 2008, a tank was emptied, to which and "air blow" is required to retrive the remaining product in the line. It was finished at 11;45am, my shift doesn't start until 12pm. After relieving someone (as igned) to stack boxes on a palate, i was told to blow air in this line, i inadvertently blew the wrong line and wasted about 60 gallons of a running line. With no previous incidents and/or mistakes, the senior supervisor gave me my 90 day review and, along with the new director of production, and HR, preceded to tell me they don't want me there until an investigation is done. I didn't get a call for 5 business days, and on the 6th, due to labor cost of cleanup i was terminated.