Separate explosions yesterday rocked two towns miles apart in northern Florida, one at a propane tank farm and the other at a chemical firm, forcing the evacuation of hundred of persons.

Two blasts ripped tanks at the Empire Gas Co. on the outskirts of the western Panhandle oil town of Jay, hurling fire and jagged hunks of metal at nearby homes and knocking out windows a mile away. Three person were injured and 300 evacuated.

Two hours later an explosion and fire struck a chemical company on Jacksonville's west side, sending up a cloud of thick, black smoke authorities said contained lethal gas.

Jacksonville officials said there were 15 injuries, none serious. Several square miles in an industrial area were evacuated following the blast at the Kenco Chemical Co., which manufactures insecticides.

A sheriff's spokesman said Durbane-6, and insecticide, mixed with the smoke billowing over the plant. Authorities had at first feared that the gas released was Parathion, a much more toxic insecticide.

Spokesman at three hospitals said the injured were being given showers to scrub off any chemicals. CAPTION: Picture, Workers clean up at a Florida propane firm after blasts injured three and forced evacuation of 300. AP