Chains, Ropes, and Slings Test I Source: Questions and answers from the National Safety Council Progress Indicator: Question 2 of 20 2.  In accordance with 30 CFR §49.6(a)(6), each mine rescue station shall be provided with at least the following equipment: Four gas detectors appropriate for each type of gas that may be encountered at the mines serve. The gas detectors must measure concentrations of oxygen from _________. Choices: 0.0 to at least 20.9 percent of volume 0.0 to at least 19.5 percent of volume 0.0 to at least 20 percent of volume None of the above