Neurocine gas
From Memory Alpha, the free Star Trek reference.
Neurocine gas is a toxic gaseous compound used by the Cardassians.
During the Cardassian Occupation of Bajor, this gas was used as a method of riot control against the Bajoran workers on Terok Nor.
In 2371, when the counter-insurgency program was accidentally activated by the Starfleet crew of Deep Space 9 space station, the ore processing center was flooded with neurocine gas in an attempt to control a worker riot. Later on, the program threatened to flood the entire habitat ring with the gas, potentially killing hundreds of innocent civilians. (DS9: "Civil Defense")
