During filming an actual fire broke out on one of the sets and Steve McQueen found himself briefly helping real firemen put it out. One of the firemen, not recognizing McQueen, said to the actor, "My wife is not going to believe this", to which McQueen replied, "Neither is mine."
Both McQueen and Paul Newman did most of their own stunts, the former having 7,000 gallons of water dumped on him, the latter climbing up and down the bent stairwell railing. McQueen also performed the stunt where he leaps off a helicopter onto the top of the burning building against Irwin Allen's wishes.
One morning on the stage containing the party/dining room set, the special effects crew began turning on the water pressure to supply the set with fire hoses needed to put out any fires left burning after the ceiling explosions. The set was built on a platform about ten feet above the sound stage floor and the main four-inch-diameter fire hose had to make a bend up and over onto the set. As the film crew waited for everything to be set prior to filming, the high water pressure caused the water hose to suddenly burst, and the pressure forced the hose to twist and turn like a giant snake. One of the special effects crew members, Gary L. King, made a decision to try to contain the hose with a big plastic trash barrel located nearby. As his struggle was being watched by the rest of the film crew, he was trying to protect the cameras and powerful lights from being hit by the spraying water. After about a minute, someone finally jumped in to help him contain the wild fire hose until the water pressure was turned off. The film crew broke into yells and claps of appreciation. Gary turned around to see who had helped him—it was Steve McQueen.