EE WAS USING AN EXTENSION LADDER TO ACCESS WHIRLSIZER TO CLEAN DEBRIS FROM SAME. READJUSTMENT OFLADDER CAUSED LATCHES TO SHIFT AND BECOME UNSTABLE. THE SUDDEN JOLT CAUSED EE TO LOOSE BALANCE A ND FALL. THE LANYARD CAUGHT EE AND PULLED HIM INTO SIDE OF TANK, STRIKING SIDE OF FACE AND HEAD AND LOSING CONCOIUSNESS MOMENTARILY.