The design of target chambers for the Inertial Confinement Fusion (ICF) Laboratory Microfusion Facility (LMF) requires a good understanding of the pressure loadings experienced by the chamber walls. Beam transport, diagnostics, and LMF applications place severe constraints on the chamber fill gas; in current light ion beam concepts only 1.5 torr-meters of helium are between the target and the closest target chamber structures. Simulations of the unavoidable vaporization of the first wall have been performed with the CONRAD computer code for a light ion beam LMF concept. Results show that the peak pressure on the wall is a function of the target x-ray power density on the wall, while the impulse on the wall is a function of x-ray fluence.