The maximum flame temperature increase for burning hydrocarbons (jet fuel) in air is, thus, about 1000 °C -- hardly sufficient to melt steel at 1500 °C." "But it is very difficult to reach [even] this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio... This is why the temperatures in a residential fire are usually in the 500 °C to 650 °C range [Cote, 1992]. It is known that the WTC fire was a fuel-rich, diffuse flame as evidenced by the copious black smoke.... It is known that structural steel begins to soften around 425 °C and loses about half of its strength at 650 °C [Cote, 1992]. This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse... The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable... Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650 °C fire." (Eagar and Musso, 2001; emphasis added.)
The maximum flame temperature increase for burning hydrocarbons (jet fuel) in air is, thus, about 1000 °C -- hardly sufficient to melt steel at 1500 °C." "But it is very difficult to reach [even] this maximum temperature with a diffuse flame. There is nothing to ensure that the fuel and air in a diffuse flame are mixed in the best ratio... This is why the temperatures in a residential fire are usually in the 500 °C to 650 °C range [Cote, 1992]. It is known that the WTC fire was a fuel-rich, diffuse flame as evidenced by the copious black smoke.... It is known that structural steel begins to soften around 425 °C and loses about half of its strength at 650 °C [Cote, 1992]. This is why steel is stress relieved in this temperature range. But even a 50% loss of strength is still insufficient, by itself, to explain the WTC collapse... The WTC, on this low-wind day, was likely not stressed more than a third of the design allowable... Even with its strength halved, the steel could still support two to three times the stresses imposed by a 650 °C fire." (Eagar and Musso, 2001; emphasis added.)