Balerium gas

Balerium gas was a substance that, if inhaled, rendered a person unconscious. It was a muscle neutraliser and also affected the throat, making speech difficult.

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. (TV: The Sun Makers)