A maintenance procedure in which a powerful beam passes along a starship to remove the baryon particles built up during warp travel, lethal to anyone left aboard.
The baryon sweep features in the episode Starship Mine. After years of high-warp travel the Enterprise-D docks at the Remmler Array above Arkaria for the treatment. Because the beam destroys living tissue, the ship is evacuated and most systems are shut down.
Picard goes back aboard to fetch his saddle and discovers that the maintenance crew are thieves, planning to remove trilithium resin from the warp engines and sell it as a weapon.
Cut off without communications or working weapons, he fights them through the empty corridors while the green wall of the sweep advances from the stern, forcing everyone towards the bow. He stops the theft, and the sweep is switched off from the planet only a moment before it reaches him in Ten Forward.