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)