Now that I can understand. In my youth we had to clean out decades of soot from the breach or live coal boilers at Wingdale, NY. The duct connecting to the huge brick chimney was big enough for a semi to drive thru. We put in a temporary huge blower, cut thru the roof and tied into the breach. Then we had to weld in plates to block the the breech so that it could be vacuumed and repaired. Want to know what it's like to have to go into 20' of soot? It took days to wash that stuff out.
My skin was black from that oil soot for a long time. I think it came off when I shed enough skin.