Using CFD to Predict Inspired CO2 and O2 after Ventilation Shutoff During a Gateway Emergency Response or Maintenance

On Gateway there are several emergency or maintenance scenarios where ventilation will be completely or partially shut off. In response to a cabin fire or toxic atmosphere, cabin intramodular ventilation and intermodule ventilation (IMV) is ceased to limit the spread of toxins. Ventilation is temporarily shut off during emergency depressurization to aid in using the hatch air direction indicator to locate the source of the leak. There are also several routine and off-nominal maintenance tasks that require complete or partial ventilation shutoff. To ensure a safe environment for the crew while ventilation is off, a computational fluid dynamics (CFD) model was developed to evaluate local concentration buildup of CO2 and depletion of O2 that arise from crewmember respiration. The model simulated a spherical crewmember’s head with realistic breathing patterns and tracked how inhaled concentrations changed over time after the fans were shut off. A variety of turbulence models, mesh sizes, crew location, and number of crew within the module were assessed. The model was used to predict the time-to-effect for crewmembers to inhale dangerous levels of CO2 or O2. Results showed the partial pressure of CO2 inspired for a single crewmember in habitation and lunar outpost (HALO) reached 10 mmHg after 2 hours, and for two crew the same concentration was reached in 1.4 hours.