If there is a nuclear blast
If there is advance warning:
Take cover immediately, as far below ground as possible, though any shield or shelter will help protect you from the immediate effects of the blast and the pressure wave.
If there is no warning:
Quickly assess the situation.
Consider if you can get out of the area or if it would be better to go inside a building to limit the amount of radioactive material you are exposed to.
If you take shelter go as far below ground as possible, close windows and doors, turn off air conditioners, heaters or other ventilation systems. Stay where you are, watch TV, listen to the radio, or check the Internet for official news as it becomes available.
To limit the amount of radiation you are exposed to, think about shielding, distance and time.
Use available information to assess the situation. If there is a significant radioactive contamination threat, health care authorities may advise you to take potassium iodide. It may protect your thyroid gland, which is particularly vulnerable, from radioactive iodine exposure. Plan to speak with your health care provider in advance about what makes sense for your family.