B Deck was a location aboard the city-sized JMC mining spaceship Red Dwarf. Near the top of the ship, it was apparently a locus of corridors, with its own service elevators, cargo bays, stasis booths and a landing bay.
When the crew decided to install a new computer named Pree, one of the tasks that Rimmer left it was to conduct some maintenance on B Deck. Pree took over the droids on the ship - the skutters and garbys - and began her task. However, when Rimmer came to inspect the work, he found B Deck in complete disarray, and in a worse state than before including exposed wiring and smoke everywhere. Asking Pree for an explanation, Pree explained that she had done the work exactly as Rimmer had done, and since Rimmer would have cocked it up, she cocked it up for him. (Fathers & Suns, Series X)
A few years later, B Deck had eventually been restored to working order. After Lister had his kidneys organ-napped by a deranged droid, the Dwarfers came up with a unique plan to reacquire some kidneys. This involved using advanced knowledge from Snacky to hack a stasis booth on B Deck to create a time portal into the past. The past Rimmer, using a Psi-Scan, detected strange energy signatures on B Deck but was kept from bumping into his future self by the actions of Shaft 14. (Give & Take, Series XI)
The Dwarfers brought aboard the crippled SS Nautilus aboard Red Dwarf on B Deck. It was here that the skutters unloaded the cargo of the Nautilus, including its bio-printer. The bio-printed captain of the Nautilus, Edwin Herring, also came aboard on B Deck, where he met the crew. After touching Lister's face, he took an instant disliking to Lister. The bio-printed Herring promptly dissolved into a pile of goo after proclaiming that his mission was complete. (Officer Rimmer, Series XI)