Usamatsu’s Glorious Life-Saving Purifier is a seal intended to remove unwanted gases from the air.
Repeatedly absorbs all gas within a 60-degree 3-metre cone in rapid bursts of suction. The gas goes into a storage space. Airlike gas is simultaneously expelled from the storage space via a separate identical cone. Anything not needed to produce the airlike gas (e.g. poison) remains trapped in the space.
Note that this seal merely removes substances from air. It does not add, so if your breathing has converted all the oxygen into CO2, the seal is not going to save you. Note also that Usamatsu had no idea about the proper chemical makeup of air, and just went with something that didn’t kill lab animals when they breathed it (in the short-term).
The seal switches between intake and outtake rapidly.
In chapter 110, the purifier seal was used to remove smokes and ashes, therefore preventing the fire from revealing the position of Team Uplift.