[Flavius Josephus]

But how would the Cintox get to where people could breathe it? It would be burned up as it came out of the pipe.

[COEXERJ145]

Remember that Sentox is a fictional gas so its properties don't correspond to real nerve gases like Sarin or VX. It does whatever the writers need it to do.

That said, they make it out to be a derivate of VX. When the gas is released inside CTU, Buchanan says over the intercom that Sentox VX-1 nerve gas has been released.

In real life, VX is much harder to destroy than Sarin as it cannot be easily burned. It takes a higher temperature to incinerate VX.