An apparatus has a first component with a first surface and a second component with a second surface, wherein the first and second components can undergo relative movement. The first surface and the second surface face each other. The first surface accommodates a barrier system to provide a barrier to reduce or prevent an inflow of ambient gas into a protected volume of gas between the first and second surfaces. The barrier system includes a curtain opening adapted for a flow of curtain gas therefrom for establishing a gas curtain enclosing part of the protected volume, and an inner entrainment opening, located inward of the curtain opening with respect to the protected volume, adapted for a flow of inner entrainment gas therefrom for being entrained into the flow of curtain gas. The apparatus is configured such that the inner entrainment gas flow is less turbulent than the curtain gas flow.