PA Mining Law - Sections 407-410 (2) Practice test questions for the PA Mine Officials' Exam Progress Indicator: Question 4 of 15 4.  Methane is most explosive at what range? Choices: 5% to 15% with at least 12.1% oxygen 9.5% to 12.5% with at least 12.1% oxygen 5% to 10% 9.5% to 10%