Respirable Coal Mine Dust Certification Exam 3 Taken from the 2014 MSHA Instruction Guide (IG) 100 Progress Indicator: Question 1 of 20 1.  Despite the constant-flow feature on approved gravimetric respirable coal mine dust sampling pumps, the _________ of those pumps must still be checked during the second and last hour of sampling by a certified person (sampling). Choices: battery voltage hose length permissibility features flow rate