The Helium Air Ingress gas Reactor Experimental (HAIRE) facility has been designed and built at the University of Michigan to study the near crack mixing phenomena and amount of oxygen ingress during the Depressurized Loss of Forced Cooling (DLOFC) and air ingress accidents in HTGRs. Oxygen ingress measurements at the University of Michigan’s scaled HAIRE facility are presented along with other pointwise measurements to compliment the current state-of-the-art HTGR air-ingress experiments. Pressure and temperature measurements are presented with estimated mass flow rates. All measurements are compared to theoretical expectations. The calculated mass flow rate, measured temperature, and measured pressure all agree well with isothermal choked flow theory. Separate oxygen ingress measurements were performed and show when temperature gradients are not present, oxygen will uniformly mix with helium in a sealed vessel. Stratification will not occur due to density differences.