THE EE WAS ASSISTING IN LOADING BARRELS OF HAZARDOUS WASTE. THERE WAS A MAT THAT EXTENDED APPROX 3"" BEYOND THE BED OF THE TRUCK. THE EE STEPPED TO THE BACK OF THE TRUCK ONTO THE MAT AND FELL A BOUT 4.5 FEET. SHE FELL ON HER LEFT SIDE TWISTING HER KNEE AND JAMMING HER LEFT WRIST. SHE WAS TAKEN TO THE ER FOR TREATMENT AND EVALUATION.