PA Mining Law - Sections 404-406 (1) Practice test questions for the PA Mine Officials' Exam Progress Indicator: Question 2 of 16 2.  Relating to the use of high pressure Oxygen, which of the following is TRUE: Choices: Do not open the cylinder valve in the presence of Nitrogen The oxygen cylinder shall meet DOT specifications and shall be marked BREATHING GAS Oxygen will not cause materials to ignite without the presence of an ignition source