NUCLEAR DETONATIONS: Nuclear detonations are the most dangerous radiation emergency. It creates a large, deadly blast. If it detonates on the ground, the explosion can suck material up into the air and create dangerous, sand-like, radioactive particles called fallout.
For a nuclear explosion, if you have warning, take cover from the blast behind anything that might offer protection. If you are outside, lie face down to protect exposed skin from the heat and flying debris. After the shockwave passes, go inside the nearest building as quickly as possible.
GET INSIDE: After a detonation, you will have 10 minutes or more to find an adequate shelter before fallout arrives. If a multi-story building or a basement can be safely reached within a few minutes of the explosion, go there immediately. The safest buildings have brick or concrete walls. Underground parking garages and subways can also provide good shelter.
Remain in the most protective location (basement or center of a large building) for the first 24 hours unless threatened by an immediate hazard (e.g., fire, gas leak, building collapse, or serious injury) or informed by authorities that it is safe to leave. Radiation levels decrease rapidly, becoming significantly less dangerous, during the first 24 hours.
STAY INSIDE: Take shelter unless told otherwise. If possible, turn off fans, air conditioners, and forced-air heating units that bring air in from the outside. Close windows and doors. Close fireplace dampers. If you are instructed to stay inside during a radiation emergency, pets and service animals should be inside too. Sheltering usually lasts at least 24 hours.
STAY TUNED: Follow instructions from emergency response officials. If advised to evacuate, listen for information about routes, shelters, and procedures. If you have evacuated, do not return until you are told it is safe to do so by local authorities.