EE WAS STANDING ON THE REAR PLATFORM OF THE WATER TRUCK TRYING TO LOOSE THE PUMP CAP WITH A WRENCH. WHILE PULLING ON THE WRENCH, THE WRENCH SLIPPED OFF THE CAP CAUSING THE EE TO LOOSE HIS BALA NCE AND FELL APPROX. 36"" TO THE GROUND. THE EE FELL ON HIS LEFT SHOULDER AND WRIST, SUFFERING A FRACTURED LEFT WRIST.