Fire Service Communications No. 1 Questions taken from Jones & Bartlett Fundamentals of Fire Fighter Skills (3rd Edition) Progress Indicator: Question 3 of 22 3.  During the gas field testing Nitrogen Dioxide (NO2) are considered correct if within ____________. Choices: +/- 5 ppm of the actual value present +/- 3 percent of the actual value present +/- 5 percent of the actual value present +/- 3 ppm of the actual value present