If there is an air raid, you must immediately take cover in a shelter or other protective place. Choose the one closest to you. You may also need to evacuate an area in case of an imminent military attack. You will be warned of an attack through air raid sirens and Sveriges Radio P4. Shelters protect against shock waves and bomb fragments. They also protect against shock waves and heat waves from nuclear weapons. Shelters provide better protection than other places against radioactive fallout, gases from chemical weapons, and biological agents.