A person died early Wednesday morning after becoming trapped in a structure fire in Rio Vista, the fire department said.Rio Vista firefighters responded to a report of a structure fire just before 1 a.m., with a victim trapped inside. When crews arrived, they found heavy fire conditions and structural compromise. While looking for the victim, a firefighter fell partially through the floor but was not injured, officials said. The victim was found dead by the time firefighters reached their location, the Rio Vista Fire Department said. Officials said the fire was placed under control shortly after 2 a.m.The cause of the fire is still under investigation. Crews from Isleton, Montezuma, Fairfield, Suisun City, Dixon and Vallejo also responded.