Sentence:  In existing buildings where no flue is available either large enough to provide a <WSD>fallway</WSD> or located conveniently for hopper doors, a basement-fed KERNERATOR provides all of the advantages except the hopper-door convenience 
Meaning of the word marked with <WSD> tags:  A well or opening, through the successive floors of a factory or warehouse or the decks of a ship, providing access for goods, material, or people.