Dear Friend:
I believe there was a tutorial in 'newtekniques' magazine, by Dave Jerrard,
which shows how to make explosions in lightwave 5.But the principles can be
easily employed to make gases. In lightwave.
If you want me to, I can dig into my lightwave magazines, and search for
the tutorials, then scan them and send to you.
Actually, one of the tutorials (if I remember correctly) was called gas with glass,
and I think it actually showed how to make gas.
Cheers !!!