Balerium gas

Balerium gas was a substance that, if inhaled, rendered a person unconscious. It had an affect on the throat, making speech hard.

The Company used the gas in its Consum Banks to target those guilty of fraud. When the Fourth Doctor went to a Consum Bank on subway 37, his consumcard was detected as a fake and the gas was released. A stretcher team took him away once the gas had dispersed. (DW: The Sun Makers)