NASA Stennis Space Center (SSC) is one of the largest consumers of gaseous helium in the world through its engine testing operations. Because helium is a nonrenewable resource, it is desirable to conserve the gas when possible. For safety purposes, helium is used to purge an engine following a test that utilizes cryogenic liquid hydrogen fuel (e.g. a Space Shuttle Main Engine test). This proposal is another important step toward enabling helium conservation through real-time measurement of the H2 concentration in the purge gas. The STTR will continue the characterization of a commercial H2 detector for use as a real-time sensor for determining the concentration of H2 in the helium purge gas. The H2 concentration can be used as an indicator that the liquid hydrogen has been purged from the engine, allowing the helium purge to be of shorter duration, thereby conserving this resource. Significant analysis of sensor capabilities as well as experimental characterization of the sensor performance in a simulated test-stand environment will be performed. A sensor configuration will be recommended with the goal of identifying the best installation option that avoids pumps, mechanical actuators, or the need to vent or pipe a sample if possible.