Shell Oil, which owned a $600-million refinery that the production wanted to use as a location, granted permission as a gesture of raising awareness about safety issues (the dangers of locating oil refineries near cities).
The filmmakers scouted Atlanta, GA; Edmonton, Canada; St. Louis, MO; and Cincinnati, OH for a location requiring several urban blocks that could be set on fire. They settled for Montréal, QC, where the entire film was shot.
Some elements of the incident depicted here reflect the Texas City disaster: On 4/16/1947, a mid-morning fire on the SS Grandcamp docked in Texas City, caused the ship to blow up, which ignited several oil refineries around the harbor. The fire detonated approximately 2,300 tons of ammonium nitrate and the ensuing fires and explosions killed at least 581 people in and around Texas City. These events also triggered the first class-action lawsuit against the US government, on behalf of 8,485 dead and injured victims.
The producers sold the film to Columbia Broadcasting System (CBS) for just over $2.6 million.
The opening credits show close-ups of several buildings. They are the Royal Bank Plaza (Toronto), recognizable with its gold-bronze windows, Place Ville-Marie (Montréal), a cruciform skyscraper, and Complexe Desjardins (Montréal), a shopping mall and office building.