INVOLVED IN A MVA DURING A SNOW STORM. RESPONDING TO A FIRE CALL DRIVING DOWN HILL WHEN VEHICLE INFRONT STOPPED IN MIDDLE OF THE ROAD. TAPPED ON BRAKES AND TRUCK STARTED TO SLIDE. TRUCK LOST CONTROL DUE TO SLIPPERY ROAD CONDITIONS .TRUCK WENT THROUGH A TREE AND TELEPHONE POLE AND MY SEAT BELTS NEVER LOCKED AND AIR BAGS DID NOT DEPLOY. TRUCKS FRONT FRAME WAS WRINKLED AND BUMPER SNAPPED IN HALF. WHILE STEPPING ON THE BRAKES SEAT BELTS NEVER LOCKED.