A New Gas - Helium

[atomic1fire]

It would be kind of neat if there was a way to add chemicals to the gas process, with a variety of side effects, such as turning the pipes into a neurotoxin delivery system, or causing the pressure in the engine to go waaay up because you added some vodka and some liquid oxygen or something.

Helium could be a fun element though, in terms of squeeky voices everywhere.