Answers to this one are good so far. However...there's more to this than meets the eye.
In victorian times, children - particularly children - were used to sweep chimneys - and many of them did actually come to dust, because during those times there were no such things as health and safety rules and regulations, no safety gear such as masks to prevent chemicals from getting into the lungs and so on. Many children did die as a result of illnesses - or indeed accidents - that occurred during the victorian times as a result of being a chimney sweep. They may have started clean, and have had a relatively good bill of health, but the work would have caused respiratory issues, and in some cases there were more severe illnesses brought on as a result of this form of employment. Children did not get an easy life - particularly in England - during this time.
Used to work in a victorian themed 'working' museum. Hated it, but I remember a lot about it.