Bonsoir Wesson et merci beaucoup pour votre réponse.

En cherchant un peu j’ai trouvé le rapport de l’ USFA (US Fire Administration) de l’attentat de 1993. On y trouve une description détaillée de la puissance de l’explosif employé.
Pour faire court la valeur calorique (Joules/kg) du Nitrate est 34 pour cent plus élevée que celle du TNT.
La bombe contenait également de l’hydrogène pour répandre l’incendie (flame de 2000°C)

Extrait du rapport :
http://www.usfa.dhs.gov/downloads/pdf/publications/tr-076.pdf

The materials involved in the WTC Bomb,

As reported in news accounts of the WTC bombing, it appears nitrourea was used as the bomb’s base and cylinders of hydrogen were used to increase the magnitude of the explosion. The following is a brief description of the materials involved.
Nitrourea, a white, crystalline powder, is a Class A explosive. It also is known as m-nitrocarbamide, N-nitrocarbonide, 1-nitrourea, and N-nitrourea. It is a high explosive that presents a severe explosion
hazard and is stable until detonated. Although some references say nitrourea is sensitive to heat and shock, the greater likelihood is that it is stable ; otherwise, it might be too dangerous to transport by truck (or van).
The power of nitrourea is similar to that of trinitrotoluene (TNT) and picric acid. (TNT and picric acid are used as reference points because TNT is referred to as the “standard” explosive in the United States and picric acid the “standard” explosive in Great Britain.) Nitrourea produces about 90.5 percent
of the gas volume of TNT when detonated and has slightly more than three percent more relative
power than TNT. It produces about 97.7 percent of the gas volume of picric acid and has three percent less relative power. Its caloric value (power as described by the number of joules of energy per kilogram of weight) is 34 percent greater than TNT’s and 19 percent greater than picric acid’s.
When compared with ammonium nitrate, nitrourea has about 13 percent less gas volume, about 38 percent more relative power, and about 47 percent more caloric value.
Hydrogen is a highly flammable, nontoxic, colorless, odorless, and tasteless gas. Its flammable range is from four to 75 percent, the second widest range of any common flammable gas. With such a wide range, it is easily ignited. The flame from burning hydrogen has a very high heat content — its flame temperature is 3,700 degrees Fahrenheit. Hydrogen burns with an almost invisible flame, converting all energy into heat energy.

L’attentat de 1993 est une preuve supplémentaire sur la bonne résistance des structures du WTC.