 know the timing of what's about to happen we're going to go outside and watch this thing from a distance you want to be at least 20 or 30 miles away from the detonation point though because the the first impact of a nuclear detonation over either one of our cities or a military base is a thermal flash which will travel at the speed of light this intense heat will ignite fires as far as 20 miles from ground zero the blast wave will follow seconds later carrying half the bomb's energy