Nagnol gas was a gas which disrupted sensory equipment in starships. It took the form of a thick cloud of smoke that curiously expanded and moved in the vacuum of space.
The Jekk'Jekk Tarr on Nar Shaddaa was once a ventilation system for passing the nagnol gasses from the docks.
During the Galactic Civil War, C-3PO used this gas to disturb the sensors of a band of space pirates attacking the Rebel freighter he was stationed onboard.