Penzance roof

I understand that HSTs are not permitted to run to the buffers at Penzance for the platforms under the roof. I believe the reason for this is that the diesel fumes can't get escape through the roof. The Voyagers/local units also emit diesel fumes though so the question is why does the restriction only apply to HSTs? I note that HSTs at Penzance seem to be using platform 4 again (although the WTT continues to show platform 1) most of the time now though.

HSTs do run into platform 1 but immediately shutdown the powercar.
Departing HSTs draw forward so the rear powercar is outside the roof and can be started for ETS.
As you say though platform 4 is mostly used now.

Why are 150s allowed to sit under the roof when the engine is running though if HSTs are not? Also when I've arrived in platform 1 on an HST it hasn't run up to the buffers so I'm not sure how often the "run up to the buffers, switch off power car and then move train away from the buffers before departure" situation described above is done.

Zoe said:

Why are 150s allowed to sit under the roof when the engine is running though if HSTs are not?

Click to expand...

Down to the levels produced possibly?

When I was down that way last month P4 was being used for almost all HST workings.

A 150 emits from each of the engines in each vehicle, A HST emits from the exhaust at the front/rear of train. A HST has a much larger engine so much higher emissions I'd imagine