A sootie is a worker of manual labor, particularly work that involves shoveling coal and ash in boiler and engine rooms. The names comes from the fact that such workers will, inevitably, become covered in soot during their work.
Many sooties are employed in the engine room of Mademoiselle Geraldine’s Finishing Academy for Young Ladies of Quality, led by Soap and later Handle. Besides shoveling coal, their duties also include running rigging and repairing the outside of the balloons when needed. Though they are not allowed to have personal relations with, or even interact with, the young ladies of the school, Sophronia has made them her allies.