The heavy reinforcing of the floors and walls of the vaults can be seen again here at the second level. The cable placed over the reinforcing may be part of a radiant heating system within the concrete structure. An in-floor radiant heating system--whether electric or hydronic--would have minimized the risk of fire in the vault as well as the amount of floor space that would need to be devoted to heating equipment. The size and number of penetrations through the perimeter walls for supply of the radiant heating system would also be reduced to an absolute minimum.