In 1979 about two shot glasses worth of anthrax was released into the air around the Soviet military facility in Sverdlovsk. The deadly biological agent was released due to a filter not being replaced. Around 105 people died because of the anthrax leak. If the wind was right that day the agent could have killed more than 100,000.
Scary history that is not discussed much if at all. Even scarier is the fact that the facility at Sverdlovsk is still open and active.