After any fire in which a building collapses, there often remain deep seated, pockets of fire deep within the rubble pile These pockets of fire sometimes cannot be reached by water streams because of their being covered by debris. Air is sometimes drawn up from the bottom of the pile and feeds these inaccessible fires with air. These fires can last for days and the heat can become intense and can heat any steel in proximity to the fire until the steel is glowing red, orange or yellow hot. These pockets of fire are common at burning building collapses and in no way evidence that that explosives or thermite were used to demolish the buildings. These fires are similar to blacksmith forge fires where air is blown into the charcoals by a bellows to raise the temperature of the fire to heat a piece of steel or iron. The blacksmith can tell how hot the steel or iron is by its color and can tell when the steel is soft enough to work it with a hammer The deep seated fires which occur in the rubble are supplied with air because natural convection currents. Heated air rises because of its bouyancy and is replaced by cool air drawn in from the bottom and sides of the fire. This air flow can become rapid because of the high temperatures developed. The more air drawn in the hotter the fire becomes and the increased temperature increases the convection currents which draws in more air. Like in a furnace the containment of heat by insulation provided by the impacted combustible material surrounding the fire allowes the gradual increase of temperature. I am convinced that temperatures of over 2000 deg F. can easily be developed in these deep seated pockets of fire in the rubble of a collapsed building.
These uancessible fires often have to be dug out by hand tools, back hoes or grapplers in order to expose the burning material for extinguishment. It is common to hold off hitting the fire with water until it is fully exposed in order to prevent the great amount of steam that would be created from obscuring the work area until the fire is fully exposed and can be quickly extinguished. This is what is happening in the picture of a grappler pulling out a piece of glowing hot steel from the debris pile so often described as molten steel. Such ordinary fires are incapable of melting steel unless they are supplied with enough oxygen.
Much has been made of the presence of molten metal in the debris pile after the collapse. Presumably this molten metal was somehow thought to be connected to explosions or thermite charges, but there were Uninterrupted Power Supply (UPS) battery rooms on some floors of the Towers and Building 7. These battery rooms supplied continuous battery power to computers if the electricity failed for any reason. These batteries contained tons of lead which melts at low temperatures [327 C (621 F)]. The heat from the fires in the debris pile could easily have melted this lead or the aluminum from the plane or aluminum from the tower’s cladding which were probably the metals that were seen flowing through the pile. NIST reported UPS in the 13th floor of Building 7 and the 81st floor of Tower 2. There were also quantities of lead, tin, silver and even gold used in the computer circuit boards.
Additionally the EPA reported over 400 different chemicals in the dust and debris. These chemicals could easily be assembled conceptually to propose any type of chemical reaction imaginable including thermite reactions. In addition thermite reactions are rapid and wouldn't last the hours or days at which times the molten metal was observed. As far as I know thermite has never been used to demolish buildings and the expertise probably doesn’t exist. Thermite is hard to control and can’t be held against the columns because it would burn down through any material used to support it against the columns.
Pure oxygen is used in oxyacetylene torches to actually ignite burn and melt the steel when cutting. These torches were used to help clear the debris pile during search and recovery operations. A slag of melted and re-solidified steel and Ferrous oxide is formed on the opposite side of the cut. This slag formation and the angle of the cuts were erroneously reported to be evidence of cutter charges having been used to sever the columns. Small molten pieces of glowing steel cool into spheres as they fly out from the cut. These steel microspheres could also have been produced during the construction of the building by welders and retained in the concrete or else ware only to be released during the collapse.