For each International Space Station (ISS) module, design of the ventilation system has been based on the assumptions that the aisle way is clean and the air supply diffusers not blocked. To avoid any impact on the function of Environmental Control and Life Support Systems (ECLSS), the space station crew is advised not to stow items in certain locations, such as airflow Keep Out Zone (KOZ). Current KOZ dimension is estimated based on the engineering approach. As there is more stowage on board of ISS, more space is necessary, and it is promising to free some cabin volume evaluating required KOZ limits more precisely. ECLSS Airflow Keep Out Zone (KOZ) requirements were relaxed in 2015, from 24” radius to 12” to accommodate more stowage. This was based on the conservative Computational Fluid Dynamics (CFD) airflow study focused on the KOZ intrusions and safety. This 80% of KOZ volume reduction resulted in 80% decrease in protrusion and violations technical assessments. However, there still are large number of violations as the ISS operation evolves, such as, new hardware, equipment, and trashes. Simple preliminary analysis was performed based on known KOZ intrusion cases. This preliminary analysis showed the current KOZ have a potential margin for a further reduction which would expand the stowage capacity on orbit at the same time would produce a safe ventilation environment. Final results showed no noticeable degradation of cabin ventilation characteristics with reduction of the KOZ. In total reduction from 24” to 6” is equivalent to ~90% reduction of the KOZ volume and increase in stowage volume in proximity to the Stand-Off area More time savings to overall ISS program for reduced inquiries and reviews. Thus, it has been recommended that, as this study has shown, reduction to 6” for the ECLSS Airflow KOZ requirement.
Son et al. (2024) studied this question.