Complex sentence: The fallout-free height, above which the radioactive particles consist only of the fine fireball condensation ones, is about 55 meters/kiloton; however even at these burst altitudes fallout may be formed by a number of mechanisms.
Split into simpler sentences: The fallout-free height, above which the radioactive particles consist only of the fine fireball condensation, is approximately 55 meters/kiloton. However, even at these burst altitudes, fallout may be formed by a number of mechanisms.