To: James Calladine who wrote (107637 ) 6/7/2007 1:37:31 PM From: cirrus Read Replies (4) | Respond to of 361346 The exhaustive fire engineering that goes into structural design calls for construction materials from steel to drywall to maintain structural integrity for a predetermined time at a certain temperature. The assumptions are that fires will be caused by careless smoking, electrical malfunctions or even arson - the usual methods. The objectives are to maintain structural integrity for a time sufficient for occupants to evacuate and the fire to be extinguished by the automatic fire systems and the fire department. The design specs did not intend for the structures to survive the impacts of fully loaded jumbo jets and fires fed by thousands of gallons of fuel. In these respects all the structures that collapsed after the 9/11 attacks performed to their design specifications. Building #7 was damaged by debris and held up for many hours before the heat of internal fires, fueled by diesel fuel and unable to be fully controlled because of equipment, water and manpower shortages, weakened the steel structural members to the point where collapse was inevitable. No laws of physics or engineering were defied. Heat steel to a certain point... it weakens and... boom! It gives way and thousands of tons comes crashing down. Conspiracy buffs don't appreciate the laws of thermodynamics. By way of example, the engine block in your car is designed to last thousands of hours, 150,000 miles or more, while containing millions of explosions over its lifetime caused by igniting gas and air - provided the engine's cooling system operates properly. If the cooling system fails the engine is scrap within ten minutes. Same with other steel products. Heat it sufficiently - to a third of the melting point - and it becomes soft enough for a blacksmith to adjust it to fit a horses hoof or cause a skyscraper to collapse. It's hard to believe that fire could cause a massive structure to collapse, or a 2 pound piece of foam to wreck a billion dollar space shuttle... but the laws of physics still apply - with spectacular consequences. NO planes hit WTC7, but it fell down anyway, defying all laws of physics, engineering...