Heartsaver First Aid Part I Progress Indicator: Question 3 of 22 3.  For the purposes of contest work, no barricade will be breached without ventilating in front of the barricade if: Oxygen (O2) is below _______, or Carbon Monoxide (CO) exceeds _________. Choices: 19.5 % O2 or 1,200 ppm CO 17.0 % O2 or 1,500 ppm CO 19.5 % O2 or 1,500 ppm CO 17.0 % O2 or 1,200 ppm CO