When you see fire in movies, it's usually real and dangerous. Computer animations are rarely used, because they neglect the intricate physics of fire-and it shows. Now computer scientists Ron Fedkiw of Stanford University and Henrik Jensen of the University of California, San Diego, have developed software that creates realistic animations of fire. Set initial conditions, like temperature, type of fuel, and surface shape, and the computer does the rest. The software solves equations that describe swirling fluids, expanding gases, and vaporized fuel, and renders effects like smoke, soot, and objects igniting. It takes about five minutes to generate each frame, but filmmakers and special-effects companies are interested. San Rafael, CA-based Industrial Light and Magic used similar techniques to create explosions for Terminator 3. But making fire animations easy to control and ready for film production will take another year or two, says Fedkiw. Other applications include virtual-reality training for firefighters.