My Gandfather use to tell stories of working as a stoker on Coal ships in Ireland when he was 14 years old or so (1912). The trick was to throw the coal in and then duck forward all in one motion. Failure to do it correctly resulted in a flash fire of coal dust hitting you in the face. He'd say:
"Not enough to seriously hurt you though, just singe your hair and eyebrows off"
Wood mills are subject to the same explosive force with wood dust explosions.