2015 Coal First Aid Statements No. 5 Taken from the 2015 National Coal First Aid Contest Rules Progress Indicator: Question 6 of 20 6.  Hydrogen Sulfide has an explosive range of ______ in normal air. Choices: 3.4 to 54.5% 4.3 to 45.5 ppm 5 to 15% 4.3 to 45.5%