I have only been to BNS once recently and that was 2 Xmas's ago. An Arriva DMU parked up and was left on and filled the air with a diesel smell. I wouldn't say it was horrible horrible but it just about borderline ok. If another train pulled in doing the same thing it would have been too much. This was a Sunday so I imagine it was quieter than usual. I believe the station was recently transformed prior to my visit.
So to put things into context -
BNS has always been underground?
Steam engines no doubt filled the whole station with an all manner of air born particles?
This is just a recent thing because of H&S pushing?
My first visit to BNS was in 1983. I remember 47's, a 46, 45's.. quite a lot of engines really. So this issue is with DMU's because the engines are under the train?
As one who remembers as a boy the pre 1960s New Street, I can reply to the questions
We did not think of New Street as an underground station until the new regulations came into effect following the Kings Cross fire. However it was below street level and it had buildings above it so it came within the definition of an underground station.
The present station at platform level is a result of the rebuilding following the WCML electrification. The recent rebuilding a few years ago did not really affect the the track layout and the facilities at platform level except for tidying them up. The main cost was in the passenger circulation above the platforms. Prior to the 1960s rebuild the station was really still two separate stations, the LNWR station and the adjacent Midland station. Each of these two stations had their own train sheds with high roofs, although the LNWR side lost its glass during the war which was never replaced. So there was much more fresh air circulating (if you could call it fresh before the Clean Air laws came into effect). The ceilings of the station since the 1960s are of course much lower than the high train sheds of the past.
Loco hauled diesel trains would mainly have their locos at the ends of the platforms which were open to the sky. DMUs on the other hand have engines distributed along the length of the train so will be producing fumes all along the platform.
