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.
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.
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!"
A burning oil well prompted the owner, present-day billionaire Phillip Anschutz, to call Red Adair, a famous firefighter who later put out the oil well fires during the Gulf War, to put out the blaze. To pay Adair, Anschutz persuaded Universal Studios to pay him $100,000 to film Adair putting out his well fire for "Hellfighters."