Cheers mate, yeah Sandsend has way too thick a layer of soot for many decent pics over a large portion of the tunnel, due to the notorious steep gradient the trains had to struggle up.
It"s documented that the Crews had to trial special masks that picked up so called "cleaner air" from the track-bed level rather than being suffocated in the huge amount of smoke as the Trains crawled along. I think it"s the thickest layer i"ve seen so far in a Railway Tunnel so far.