Ventilation No. 5 Questions taken from Jones & Bartlett Fundamentals of Fire Fighter Skills (3rd Edition) Progress Indicator: Question 4 of 12 4.  What is the source of methane in coal mines? Choices: It is liberated from coal and adjoining strata. It is the chemical combination of water and carbon. It is the chemical combination of air and carbon. It is the chemical combination of oxygen and hydrogen.