An egress door is an exit designed to allow the occupants of a building to evacuate safely during an emergency. In most countries, such doors are regulated by local building codes, which stipulate how many doors are required and the requirements for each exit. In the United States, most building codes relating to these doors are based on standards developed by the National Fire Protection Association (NFPA). NFPA Standard 101 stipulates have an egress door should be operated, installed and controlled. The NFPA guidelines are based on the building's function and occupant load, as well as on the presence of hazardous or combustible materials.