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For now, this is a collection of notes about temperatures believed to have been achieved within the WTC fires, and temperatures at which various things happen to materials (especially structural steel) known to have been used in the WTC construction, for comparison purposes.

These figures are preliminary; sources need to be found, and these numbers need to be compared with figures found in other 9/11 literature (official and otherwise).

See also: Issuepedia:Archive/Corus Construction/fire/6. Steelwork Fire Resistance for some data on how steel's strength changes with temperature.


Critical temperature is the temperature at which a structural element cannot safely support its load. (Presumably the size of "load" is based on a rating for that particular material.) This temperature is often defined as the temperature at which the element's yield stress has been reduced to 60% of the room temperature yield stress.

Comparison Table

Numbers in italics have been converted from figures given in the other measure of temperature.

°C °F description source
452 hottest temperature achieved in samples metallurgically analyzed by NIST (the samples analyzed were those believed to have been closest to the hottest parts of the fire) somewhere in NIST
400 752 in Japan, the critical temperature is apparently considered to be below this from Wikipedia, no source
425 800 structural steel begins to soften Eagar 2001
538 1000 lower end of critical temperature in China, Europe and North America (e.g., ASTM E-119) Wikipedia citing offline source
650 1200 max temperature for typical residential fire (upper estimate) Eagar 2001
650 1200 structural steel loses half its strength Eagar 2001
700 1300 upper end of critical temperature in China, Europe and North America (e.g., ASTM E-119) Wikipedia citing offline source
800 "highly unlikely" that WTC steel experienced temperatures higher than this Eagar 2001
930 1700 maximum temperature of open flame ?
982 1800 hottest temperature claimed in NIST report (not supported by their own metallurgic analysis of actual samples) somewhere in NIST
1093 2000 fire-rating of steel used in WTC construction, good for 6 hours ?


There may be some additional information in Eagar 2001.