Ottumwa firefighters are investigating a Wednesday morning (3/2) arson fire.  The City of Ottumwa says its Fire Department was called to a structure fire at 734 Center Street shortly after 8am.  Fire crews quickly put out the blaze.  Once that was done, investigators found several fires had been started in the two story home, which is a sign of arson.  The house was vacant and utilities had been turned off.  If you have information or surveillance cameras in the area, contact the Ottumwa Fire Department at 641-683-0666, extension 3.