There are multiple types of building collapses:

Pancake, basically where floors dislodge from the wall structure and create a pancake like collapse, often seen in high-rise type buildings, parking garages. I have seen photos of the Mexico City earthquake showing several buildings collapsing in this fashion. Voids are not common and the sheer weight of the debris leaves little area for survival.

"V" collapses, where the floor(s) cave(s) in from the central area of the building, still or somewhat still attached to the wall structure. This type of collapse creates major void areas on either side of the "V". Survival is greatly enhanced in this type of collapse.

Cantilever collapses are similar to "V" collapse, in the creation of void spaces. This type of collapse occurs when a wall collapse and the floor(s) cantilever on one side. This type of collapse again creates survival areas.

Most office furniture is not designed to absorb all the impact and weight of a collapse and therefore hiding under them will generally not increase survivability. Survivors have been found near/next to office/household furniture as opposed to underneath the items.

Pete