Beam-Gas Simulations for 2009 LHC Running and First Comparisons with Data

This notes describes the calculations made for the pressure maps, beam-gas events and lifetime for comparison to the first machine running at the end of 2009 at a beam energy of 450 GeV. This includes a full set of pressure maps and equations to calculate beam-gas. The beam-gas loss rates around the machine, and the expected flux of beam-gas induced background particles into the LHCb and ALICE experiments are calculated. Wherever possible at this early state, the consistency ofthe measured beam-gas rates and the simulations is assessed.