There were stairs leading to the basement, warehouses are usually pretty tall, since they have to make room inside for cranes, huge containers, etc. And because of it being a warehouse, there had to be huge beams, columns, maybe shelving. And that bldg. was dynamited.......which means a lot of concrete & rubble. Big beams, roofing, steel, huge walls. We saw where Andre' was when he HEARD that the explosion was imminent. He ignored it. Guess he figured he is a DiMera, therefore invincible.
And when a bldg is blown up and comes down, the end loaders are there to shovel all the debris onto big trucks to be hauled away.