firestop

[fahyuh r-stop]
noun
  1. any object built into a building frame to block a concealed hollow space through which a fire might pass from one part of the building to another.

Origin of firestop

An Americanism dating back to 1895–1900; fire + stop
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018