USCF Rules of Chess, P. 37-38.
14H. Insufficient Losing Chances
14H. Claim of Insufficient Losing Chances in Sudden Death
In a sudden death time control, a player with less than five minutes of remaining time may stop the clock and ask the director to declare the game a draw on the grounds that the player has insufficient losing chances.
The draw shall be allowed if the Director believes that a Class C player would have little chance to lose the position against a Master with both having ample time. The exact losing chances of any position cannot be calculated, but a Director wishing a more precise standard may consider "little" to mean less than 10 percent. A Director unsure whether the position meets the above standard should temporarily defer a ruling by using option 14H4c or 14H4d.