Roll caster (11) produces thin steel strip (12) formed on casting surfaces (22A) of casting roll (22) that passes through first enclosure (37) adjacent casting roll surfaces (22A) and, optionally, thereafter second enclosure (61). Enclosure (37) and/or enclosure (61) may be fitted with spray nozzles (71,72) and/or (67, 68) operable to spray fine water mist adjacent strip (12) to produce hydrogen gas in enclosure (37) while tending to avoid liquid water contact with steel strip (12) and casting surfaces (22A). If hydrogen gas is produced only in enclosure (61), the two enclosures (37, 61) are interconnected so that gas can flow from enclosure (61) to enclosure (37). Enclosure (37) and, if present, enclosure (61) are sealed to maintain positive pressure and oxygen levels less than the surrounding atmosphere, and with the presence of hydrogen gas, reduce formation of scale on the strip in enclosure (37) and, if present, enclosure (61).