I happen to know a thing or two about "non toxic gas". There are gases called "simple asphyxiant" which can be safely breathed with 20% oxygen. You are doing this now by breathing a blend of 20% oxygen and 80% nitrogen.
Noble gases are simple asphyxiat, He, Ne, Ar, Kr Although there likely wouldn't be a need to use Kr as it would be more expensive. Sulfur hexafluoride is another very heavy gas. Of course N as mentioned above.
So there are plenty of truly non toxic gases that can be easily detected by a mass spectrometer, but impossible to notice otherwise. Depending on the molecular weight and boiling point of the compound(s) will affect distribution. Something like propylene glycol is nearly odorless and non toxic and would be high boiling liquid.
As skeptical as I normally am, I'm inclined to believe that this is possible and there is precedence of subway attacks (Tokyo 1995). They could be testing drug dispersal, but most drugs are too high boiling to spread via atmosphere, while there are toxic gases that are light.
Fun fact. Any gas that is not colorless is toxic. There are colorless and odorless gases that are toxic (CO for example) but colored gas is always. Cl and NO for example
I happen to know a thing or two about "non toxic gas". There are gases called "simple asphyxiant" which can be safely breathed with 20% oxygen. You are doing this now by breathing a blend of 20% oxygen and 80% nitrogen.
Noble gases are simple asphyxiat, He, Ne, Ar, Kr Although there likely wouldn't be a need to use Kr as it would be more expensive. Sulfur hexafluoride is another very heavy gas. Of course N as mentioned above.
So there are plenty of truly non toxic gases that can be easily detected by a mass spectrometer, but impossible to notice otherwise. Depending on the molecular weight and boiling point of the compound(s) will affect distribution. Something like propylene glycol is nearly odorless and non toxic and would be high boiling liquid.
As skeptical as I normally am, I'm inclined to believe that this is possible and there is precedence of subway attacks (Tokyo 1995). They could be testing drug dispersal, but most drugs are too high boiling to spread via atmosphere, while there are toxic gases that are light.
Fun fact. Any gas that is not colorless is toxic. There are colorless and odorless gases that are toxic (CO for example) but colored gas is always. Cl and NO for example