Post-flight analyses of Columbus HEPA filter

The current corrective maintenance approach for the Columbus cabin HEPA filter (High Efficiency Particulate Air) does not consider possible microbial growth. Thus, it has been proposed to perform a one time exchange and download of the filter after about 2 years of operation, with subsequent microbiological and chemical analyses to evaluate the potential change from corrective to preventive maintenance approach. The analyses were carried out to identify the microorganisms present on the filter and the composition of the matter collected on its surfaces (on account to its role in supporting bacterial and fungal growth). The majority of microbial species detected was represented by fungi (Penicillium spp. was the most widespread fungal genus) and Gram positive Staphylococci among bacterial colonies. Bacterial contamination probably originates from humans, whereas fungi are likely originated either from humans and spacecraft. Chemical contamination is related with food (salts and vegetables), fragrances commonly present in personal care products and plastic materials off-gassing. Load analyses have shown that a corrective maintenance based on the differential pressure sensor readings seems not to be significant. On the basis of the results, Joint Engineering Control Board has endorsed to change Columbus HEPA filter maintenance from corrective to preventive, by stating that the time between two changes shall have a good margin to allow flexible operation. The study was in collaboration with University of Piemonte Orientale A. Avogadro and SMAT (Società Metropolitana Acque Torino) Research Center.