Ee had begun to clean the riser with a water lance, when a large piece of build-up dislodged. As the material fell, some of it struck the end of the lance causing it to hit the Ee's aluminized hood. The Ee's hood flew up striking the Ee on the cheek and causing a laceration. The employee had to have 8 sutures to close the wound which was approx 1"" in length.