An exhaust assembly for a fuel cell system, comprising a plenum having an inlet configured to receive a gas flow from the fuel cell system and an outlet configured to vent said gas flow to atmosphere, the plenum including a louvre assembly for controlling the flow through the plenum between the inlet and outlet, wherein the plenum includes a purge gas inlet downstream of the louvre assembly configured to introduce a purge gas of the fuel cell system into the gas flow for dilution thereof, the louvre assembly configured to induce, in use, a lower pressure region proximal the purge gas inlet relative to a region distal the purge gas inlet within the plenum.