EE WAS ON THE 3RD STEP FROM THE BOTTOM OF A 10' EXTENSION LADDER. HE WAS REACHING UP TO CLOSE A 2""GATED AIR VALVE. USING A 12""WRENCH TO CLOSE VALVE TIGHT, VALVE BONNET CAME OFF, RELEASING THE PRESSURE STORE IN APPROX. 30'OF 2""HOSE. EE WAS STRUCK BY WRENCH OR VALVE BONNET AND FELL FROM THE LADDER. HE TRIED TO BREAK HIS FALL WITH HIS HANDS AND FRACTURED BOTH WRISTS.