Qualifies· moderateSEP-E010
The unexplained sulfidation, and the study its authors asked for and never got
- what the source states
- "Evidence of a severe high temperature corrosion attack on the steel, including oxidation and sulfidation with subsequent intergranular melting, was readily visible in the near-surface microstructure. A liquid eutectic mixture containing primarily iron, oxygen, and sulfur formed during this hot corrosion attack on the steel." And, on the open question: "The severe corrosion and subsequent erosion of Samples 1 and 2 are a very unusual event. No clear explanation for the source of the sulfur has been identified. The rate of corrosion is also unknown. It is possible that this is the result of long-term heating in the ground following the collapse of the buildings. It is also possible that the phenomenon started prior to collapse and accelerated the weakening of the steel structure. A detailed study into the mechanisms of this phenomenon is needed to determine what risk, if any, is presented to existing steel structures exposed to severe and long-burning fires."
- what we infer
- A genuine documented anomaly that no one has resolved in either direction, because the study its own authors requested has never been performed. Note what the appendix does NOT do: it proposes no source for the sulfur at all. The frequently repeated attribution of a gypsum explanation to these authors is mistaken; their stated alternatives concern when the corrosion occurred, not where the sulfur came from.
- limitations
- Two members recovered opportunistically, with hedged identifications ('appeared to be', 'thought to be') rather than documented provenance.
- The appendix's own leading possibility is post-collapse heating in the debris pile, which would carry no implication for the collapse mechanism.