Then the explosion is expanding at an instantaneous rate of:
(10 meters [radius] / 0.001 sec) = 10,000 meters per second = ~6.2 miles per second.
Obviously it won't sustain that velocity, but still. That's insane(ly awesome).
The upshot of this is that the entire sphere that you see comes into existence in a roughly simultaneous fashion, not in an expanding fashion. If you watch slow-motion videos, you will see that sphere stay at the same size and transition from dark to light, rather than start light and transitioning from small to large.
The explosion itself comes later, as that air (which is around 9000F) obeys basic gas laws, and tries to expand.