ignite vs touch off

ignite

verb
  • to spark off (something), to trigger 

  • to commence burning. 

  • to set fire to (something), to light (something) 

  • To subject to the action of intense heat; to heat strongly; often said of incombustible or infusible substances. 

touch off

verb
  • To start; to cause, especially used for unstable situations that may magnify if disturbed. 

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