The temperature necessary to melt structural steel ranges from 2000 degrees fahrenheit to 3000 degrees fahrenheit dependent on the specific alloy composition of the steel
The temperature of burning gasoline is about 500 degrees fahrenheit. The temperature of burning kerosine (jet fuel) is about 450 degrees Fahrenheit.
Structural steel begins to sag at about 1025 degrees fahrenheit
See PHYSICAL CONSTANTS for the information.
I was the construction superintendent on a project for the repair of a structural steel building damaged by fire. The fire was fueled by plastic and polystyrene packing of one thousand or so flourescent flight fixtures in storage. Such fixtures are of the kind often seen in commercial office spaces.
Polystyrene burns at a temperature of about 925 degrees Fahrenheit or at about the temperature when structural steel starts to distort and about twice the burning temperature of gasoline or jet fuel
The steel columns had 2 inch steel flanges and had become slightly distorted as the result of the polystyrene fire.
The steel columns were straightened by a specialist whose business card had the motto "Have Torch, Will Travel" Mr. Ray Stitt was the specialist that used heat treating with an acetylene torch to straighten structural steel. You can read about him on the web at STRAIGHTEN STEEL WITH HEAT It is a PDF file and you have to go pages 14-16.
The procedure that he used had to be certified by a structural steel engineer before the State Owner of the building would permit the process to be used
Mr. Stitt came to the basement of this 10 story structural steel and concrete building where the fire had caused the damage and set up his acetylene torch and its tanks to get to work.
Because of the New York City labor contracts, the steel workers claimed the work but as Mr Stitt set up to do his work they stayed by the exits to make a quick getaway. The procedure was simple. Mr. Stitt drew a triangle with a heat sensitive blue chalk that disappeared when the temperature of the steel reached 900 degrees Fahrenheit. The triangle was drawn with one of the apex at the opposite side of the distortion. At the temperature of 900 degrees Fahrenheit, MR. Stitt’s assistant flooded the heated section with cold water. The steel reacted by contracting and straightening out the distortion
Once the steel workers had watched the procedure for several times they quickly joined Mr. Stitt in working on the procedure at other columns under his supervision.