EE WAS DRIVING CO TRUCK WITHOUT PERMISSION. THIS TRUCK HAD TRANSMISSION PROBLEMS AND WAS STOPPED& OUT OF SERVICE IN OUR FACILITY. SUPERVISORS & MECHANICS ADVISED HIM NOT TO DRIVE IT UNTIL THEY FIXED IT. HE DIDN'T CARE AND USED IT CAUSING A FIRE ON THE VEHICLE. WHEN EE TRIED TO COMBAT THE FIRE, STEAM AFFECTED HIS FACE PRODUCING IRRITATION. THE CO HAS SUSPENDED THE EE FOR 2 WEEKS.