F=ma? It's a truism, but it doesn't dictate in quite the way you think. Think of an explosion as the creation, instantaneously, of a bubble of hot gas about the size and shape of the container of explosive. The gas will expand, with pressure on any resisting surface. If it is inside something, it can tear it apart. If it is outside of something, it can slam it really hard. Hard enough to break it into pieces. Things farther away will be afflicted with a shock wave and a tremendous wind.

Which reminds me, if the detonation is standing off from the confining surface, the shock wave may reflect off that surface and cause an exponential increase in the static pressure.