The news truck seen at the first fire carries the markings of KPRC Channel 2, which is a real Houston NBC affiliate. The reporter, Chris Chandler was an actual KPRC reporter as well.
Jay C. Flippen had a leg amputated due to infection in 1965 while filming Cat Ballou (1965). That is why he played Jack Lomax as being wheelchair bound, with the reason given that the character had broken his back fighting a fire.
When asked to comment on the film during production, actress Katharine Ross replied, "It's the biggest piece of crap I've ever done!" Then the reporter asked Vera Miles to respond to Ross's comment. She thought for a moment and said, "Well, it's not the biggest piece of crap I'VE ever done!"
John Wayne, who turned 61 during filming, was ten years older than his real-world alter ego, Red Adair. With such blockbuster films as True Grit (1969) and The Cowboys (1972) still ahead of him, Wayne was a big enough box office draw to play quite a few roles that were too young for him.