AT END OF 10 HR. SHIFT EMPLOYEE CHOSE TO USE 2' X 4' FORM AS LADDER TO CLIMB UP A 3' EMBANKMENT FROM CONCRETE FORMING OPERATION. LOW-SLOPE WALKWAYS WERE PROVIDED AT EACH END OF 18' TRENCH FOR EGRESS. AN EXTRA 2' X 4' SYMON FORM LYING ON THE GROUND TEMPTED THE EMPLOYEE TO USE IT A S A LADDER BUT IT WAS NOT STABLE AND MOVED CAUSING LOSS OF TRACTION RESULTING IN A SLIP & FALL TO KNEE.