IMBL, forgive me, for I am 100% sure that the collision sphere are not linked to any explosion
As for merchants (and other breakable vessels), please have a look at the damage models of the fore and aft hull halves. You will be astonished how many sphere you find there ... the main model of all breakable ship have usually just very few spheres close to the position where the hull is supposed to split.
Spheres only define the shape of objects that can collide with other objects.
Cheers