One of the dirty little secrets of our old smoke simulation is that in spite of being implemented in what was originally an incompressible fluid solver, the various pokes and prods that we do to the divergences and pressures can cause the simulation to break. As a result, it's necessary to set some starting parameters in the fluid grid so that the sudden injection of stuff from the explosion doesn't cause the solver to freak out.
One of the little problems of this is that after several months pass, it can be easy to forget just what all the little constant tweaks were in order to get particular explosions. Alas.
Here are some pictures of explosions that Steve Lovejoy and I simulated from the past project: