During vehicle submergence, at least 1 window per row of seats shall be able to be opened to allow occupant escape, and shall remain openable for at least 2 minutes from water entry. The vehicle shall be lowered into a water-filled container within a 10-degree horizontal angle in X longitudinal and lateral directions. T0 is counted from when lowering straps slacken and the vehicle floats. After 2 minutes of floating, the window must be opened to its lowest position, or automatically lowered if equipped with automatic window lowering system. Alternative sub-system tests demonstrating window opening functionality under water, in agreement with the approval authority and its designated technical service, are acceptable. The test is fulfilled if the window is open to its lowest position after the test.