Question 990 Deck General

The correct answer is B) critical dilution line. The critical dilution line on a hydrocarbon flammability chart represents the minimum oxygen concentration required to maintain a flammable mixture. This line extends from 0% to 21.8% oxygen and is tangent to the flammability range, indicating the boundary between flammable and non-flammable mixtures. Below this line, the oxygen concentration is too low to support combustion, while above this line, the mixture is not flammable. The other options are incorrect because: A) The minimum oxygen content line is not the same as the critical dilution line. C) The critical displacement line is a different concept related to the displacement of oxygen by an inert gas. D) The upper threshold limit is not a specific term used in the context of hydrocarbon flammability charts.