Radiation Exposure.

Stay inside your home or office unless instructed by civil authorities to leave. Close the windows, turn off the heating or air conditioning, and stay near the center of the building. Once the initial blast is over, radioactive materials may be spread in the smoke and debris in the air. By staying inside you will reduce any potential exposure to airborne radioactive material. If there is a basement, go there.

[1]  H. Newell,et al.  Radiation environment in space. , 1960, Science.