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Strategies & Market Trends : Mish's Global Economic Trend Analysis

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To: Think4Yourself who wrote (51487)	5/18/2006 7:23:56 PM
From: Elroy Jetson	Read Replies (1) of 116555

The primary purpose of sprayed concrete on steel girders is to protect the steel from heat in a fire. It does not provide structural strength. This random website lists these possible problems. public-action.com lack of insulation Some have raised questions about the degree of fire protection available to guard the structural steel. According to press reports, the original asbestos cementitious fireproofing applied to the steel framework of the north tower and the lower 30 stories of the south were removed after the 1993 terrorist truck bombing. higher temperature than estimated due to exothermic destruction of aluminum Others have pointed out the possibility that the aviation fuel fires burned sufficiently hot to melt and ignite the airliners' aluminum airframe structures. Aluminum, a pyrophoric metal, could have added to the conflagrations. Hot molten aluminum, suggests one well-informed correspondent, could have seeped down into the floor systems, doing significant damage. "Aluminum melts into burning 'goblet puddles' that would pool around depressions, [such as] beam joints, service openings in the floor, stair wells and so forth...The goblets are white hot, burning at an estimated 1800 degrees Celsius. At this temperature, the water of hydration in the concrete is vaporized and consumed by the aluminum. This evolves hydrogen gas that burns. Aluminum burning in concrete produces a calcium oxide/silicate slag covered by a white aluminum oxide ash, all of which serve to insulate and contain the aluminum puddle. This keeps the metal hot and burning. If you look at pictures of Iraqi aircraft destroyed in their concrete shelters [during the Persian Gulf war], you will notice a deep imprint of the burned aircraft on the concrete floor. .

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