Unknown gas was sprayed at the VDNKh metro station

An unknown gas was sprayed at the VDNKh metro station, my mother informed me about this. She was going down the escalator, when it became difficult to breathe, people panicked and ran up the escalator.

What and how it happened is really unknown ... Reinsure yourself in these matters will not hurt, avoid the metro, warn your loved ones.

It seems that everything works in normal mode, so most likely it was a banal bird cherry