Abstract: An open-topped vessel for converting molten ferrous metal to steel is pivotal about a horizontal axis and has bottom tuyeres for blowing oxygen or other gases upwardly through molten metal. An enclosure at least partially surrounds the vessel and cooperates with a smoke hood to prevent the escape of pollutants when the vessel is in its vertical position. A pair of access doors are provided for closing an opening provided in the enclosure laterally of the vessel tilt axis and are mounted for movement in opposite directions. An auxiliary smoke hood is mounted in the enclosure above the opening for capturing pollutants when the vessel is tilted toward said opening for being charged. The inner surface of the doors are formed of a plurality of self-mounted cast iron plates.