The power of the explosion was such that the 7-foot ( 2.1 m ) deep concrete walls ( replicating how archives suggest the walls of the old House of Lords were constructed ) were reduced to rubble .
The power of the explosion , which surprised even gunpowder experts , was such that seven-foot deep solid concrete walls ( made deliberately to replicate how archives suggest the walls in the old House of Lords were constructed ) were reduced to rubble .