airlock vs obstruction

airlock

noun
  • A sealed, airtight chamber, such as in a manned spacecraft or submarine, used to provide access to and from the sealed area without allowing air out or water in. 

  • A vestibule, foyer or entranceway with doors to the exterior on one end and doors to the interior on the other, functioning to keep indoor and outdoor air, humidity, and air temperatures separate. 

obstruction

noun
  • Something which obstructs or impedes, either intentionally or unintentionally 

  • The act of obstructing, or state of being obstructed. 

  • The condition of having the natural powers obstructed in their usual course; the arrest of the vital functions; death. 

How often have the words airlock and obstruction occurred in a corpus of books? (source: Google Ngram Viewer )