if you have black dust in your home from anthricite, it is COAL DUST not soot. one creates this coal dust from being somewhat careless in handling coal. when you dump coal, move it, shevol it etc. if you are not carefull you will creat dust, simply modify the way in which you handle coal to minimize and eliminate the dust. no it is not really harmfull over a short period, however, it can and should easily be eliminated, there is no reason why you should have coal dust, soot, or ash etc. throughout the home. modify the way you do things to fix this problem.