Southwest Regional Drager BG4 Exam Taken from the 2019 Southwest Regional Mine Rescue Contest held in Ruidoso, New Mexico Progress Indicator: Question 2 of 30 2.  In addition, gas detectors must measure concentrations of methane from 0.0 percent to 100 percent of volume, oxygen from 0.0 percent to at least 20 percent of volume, and carbon monoxide from 0.0 parts per million to at least 9,999 parts per million. Choices: True False