Steam in the Moffat Tunnel

Not wanting to further hijack the 318 green boiler jacket thread, I am starting a new one.
In the previously mentioned thread there has been some discussion about steam operating in a tunnel. The Moffat tunnel is 6.2 miles long and was completed in 1928. Steam passed through it regularly, as did passenger trains pulled by steam.
I have a friend who works as a conductor on the BNSF who tells me that conductors and engineers on the Moffat Route need scuba certification.

I am wondering what the steam engine crews did when passing through the Moffat Tunnel? I imagine that smoke in the confined area created quite a problem.