I WAS BACKING MY CAR UP TO UNLOAD A SHELF AT WORK. I WAS BACKING A SHORT DISTANCE( 15 FT) ON A FLAT SURFACE.THE TAILGATE OF THE CAR WAS UP. I HAD TO TURN THE CAR SLIGHTLY TO THE RIGHT TO BACK IT TOWARDS A HANDICAP RAMP. MY CAR WAS ROLLING SO I WAS USING THE BRAKE AND MOVING SLOWLY WHEN MY CAR ACCELERATED BACKWARDS. I WAS PRESSING MY FOOT ON THE BRAKE, ALMOST STANDING ON IT , AND MY CAR ACCELERATED THROUGH THE RAILING ONTO THE RAMP WHILE MY FOOT WAS ON THE BRAKE. THIS RAILING WAS ABOUT 35 FT LONG AND HAD 7 POST THAT WERE CEMENTED INTO THE RAMP. THE WHOLE RAILING WAS KNOCKED DOWN. TWO OF MY COWORKERS WERE STANDING ON THE RAMP WAITING TO HELP UNLOAD THE SHELF WERE INJURED. BOTH COWORKERS HAD BROKEN LEGS THAT REQUIRED METAL RODS. ONE COWORKER HAD A MORE SERIOUS LEG INJURY AND WILL REQUIRE MULTIPLE SURGERIES AND SKIN GRAFTING.