Biomass (e.g., plant biomass, animal biomass, and municipal waste biomass) is processed to produce useful intermediates and products, such as energy, fuels, foods or materials. For example, systems and methods are described that can be used to treat feedstock materials, such as cellulosic and/or lignocellulosic materials, in a vault in which the equipment is protected from radiation and hazardous gases by equipment enclosures. The equipment enclosures may be purged with gas.