>>4371061Photo of a bus full of hostages that were released after gas usage by special forces during Nord-Ost terrorist attack, 2002. Most of them are dead. They died because of asphyxia - poisoned people were placed lying on their backs, making them choke on their tongues and vomit. Nobody knows exactly what type of gas was used.
https://en.wikipedia.org/wiki/Moscow_theater_hostage_crisis 