Oliver Stone's ambition for World Trade Center was to present an accurate story, true to the survivors and their families. The visual effects sequences had to be as realistic as possible, yet convey the full impact of the events that took place that day.
Animal Logic's brief was to recreate the interior lobby and concourse of Tower 2, when it collapsed on survivors John McLoughlin (Nicolas Cage) and Will Jimeno (Michael Pena) on September 11, 2001. The sequence begins with an immense fireball descending on to the street, followed by a massive ash cloud - the result of the collapsing tower. As the lobby and concourse area are engulfed, McLoughlin, Jimeno and other officers run for the elevator shaft for protection.
The recreation of the scene was complex not only due to the level of CG expertise required to achieve the sequence, but because there was literally no visual reference of the interior collapse of the Towers. The team had only the testimonials from survivors McLoughlin and Jimeno, from which many of the effects details were based.
Each shot included as many as 200 layers of effects, combining digital and live action elements such as dripping water, vibrating water, splashes, shattering glass, cracking concrete, electrical sparks, dust, rocks, paper and fire. Additionally, to create the ash cloud, artists used a combination of techniques including particle simulations and proprietary tools designed to create accurate timing, motion and look of the cloud.