City of Houston Fire Department (HFD) is the agency that provides fire protection and emergency medical services for the city of Houston, Texas, United States, the fourth largest city in the United States. HFD is responsible for preserving life and property for a population of more than 2 million in an area totaling 654 square miles (1,690 km2). The department is the largest fire department (by number of personnel) in the state of Texas.