FEMA Appendix C: sulfidized / eutectic-attacked steel samples

Observation

FEMA published photomicrographs of WTC steel with unusual sulfidation/eutectic thinning and said the sulfur source was unidentified.

Interpretation

Open materials question. Frequently labelled a CT talking point; it is first an official appendix. Do not upgrade it to a thermate proof; do not drop it.

Source text

OBSERVATION (FEMA 403 Appendix C, Barnett/Biederman/Sisson, WPI): Recovered WTC steel showed intergranular melting / sulfidation and a eutectic that thinned plates. Authors called it a very unusual event and said the sulfur source was unidentified.

INTERPRETATION A (official later): contamination, or gypsum, or fire-related chemistry, not a demolition product. NIST did not treat Appendix C as evidence of explosives.

INTERPRETATION B (Jones/Harrit and others): high-temperature sulfur-bearing attack is consistent with thermate (thermite + sulfur).

The lab stores the materials observation and both interpretations. The steel itself was not retained as a public reference collection.

Hypothesis linkage

• H004weakly supportsseeded

  FEMA Appendix C unusual sulfidation; thermate-compatible, not unique.