Ropes and Knots No. 2 Questions taken from Jones & Bartlett Fundamentals of Fire Fighter Skills (3rd Edition) Progress Indicator: Question 3 of 20 3.  Which one of the following best describes the oxygen consumption of a normally functioning human being? Choices: The body requires a constant supply of oxygen at 79%. The human body needs a minimum of 10% oxygen to survive. The body exhales an average of 21% carbon dioxide with each breath. The average exhalation contains an oxygen concentration of between 10% and 16%.