Safety interlocks
From Tardis Wiki, the free Doctor Who reference
The safety interlocks were a system in a TARDIS which prevented it from materialising within a solid object. The Seventh Doctor destroyed a Lobri by setting his TARDIS to materialise within the main Lobri, destroying it; the safety interlocks would have prevented this action. (COMIC: Ground Zero [+]Loading...["Ground Zero (comic story)"])
