EE was replacing a nozzle on a wash hose. Piece of coal (20""x8""x3""thick) slid down the rib and struck right hand. EE moved the wash hose valve next to the rib which was protected with wire mesh within 3' of the floor.EE was earing keviar gloves. Same knuckle was fractured of the job 3 months prior resulting in this re-fractured. No external marking or bruising of skin.