Rip cord

from The Collaborative International Dictionary of English v.0.48

Rip cord \Rip cord\
   1. (Aeronautics) A cord by which the gas bag of a balloon may
      be ripped open for a limited distance to release the gas
      quickly and so cause immediate descent.
      [Webster 1913 Suppl.]

   2. a cord which, when pulled, opens a parachute.
      [PJC]