# Why does the ISS crew wear a dust mask in BEAM?

This video from NASA shows Jeff Williams entering BEAM for the first time. He's wearing a simple dust mask. Why is that? If there is concern about floating particles, wouldn't there be a concern with leaving the hatch ajar?

• Really good question!! One of the constant concerns on the ISS is inadequate air circulation as a consequence of microgravity as well as long, narrow, tunnel-like architecture, which could lead to local build-up of $CO_2$ or contaminants. So there's a whole network of recirculation ducts and fans to avoid "dead space". You (or I) might ask if, in addition to the hatch being open, if there is forced circulation through the hatch as well. Either way has consequences. – uhoh Jun 8 '16 at 1:31
• Note the goggles as well. This suggests to me it is a particle/dust concern. Perhaps the safety risk of having the hatch to an untested module closed with someone inside just outweighs the risk of dust circulation? – Andrew Jun 8 '16 at 7:37
• I think I'd want a tethered line on me on these first few inspections of the BEAM. Just in case the skin rips and I need out of there really quick. – Howard Miller Jun 10 '16 at 1:00

• This doesn't really explain why it's standard procedure, though. Presumably it's because of particulates, but I don't think that mask is doing much to protect against a "local build-up of $CO_2$". – Chris Jun 8 '16 at 17:41