flaring vs smouldering

flaring

noun
  • The act of something that flares. 

  • The deliberate open-air burning of natural gas that is generated as a by-product of various petrochemical processes, especially oil extraction; gas flaring. 

smouldering

noun
  • The act by which something smoulders; residual heat. 

adj
  • Burning slowly, producing smoke but no flame. 

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