Despite their extensive and every-day involvement with the processing of combustible, explosive, and toxic materials under conditions that include extreme temperatures and pressures, the chemical and petroleum industries (CPI) have a commendable, if occasionally scarred, record, with respect to safety. The practices and guidelines that have lead to this record evolved in part on the basis of scientific and technical principles, but perhaps in greater part from analysis of the accidents that did occur. The World Trade Center disaster on September 11, 2001 has perhaps evoked to more technological analysis and comment than any other such singular event. These analyses are epitomized and largely pre-empted by the investigation of the National Institute of Science and Technology (NIST) as summarized by Grosshandler. That analysis, which is based on direct observations and backed up by dedicated experimental work, is to be commended for its scope, focus, and objectivity. In consideration of the existence of that report, there might appear to be no need for a further study, but we found a few unresolved issues. The objective of our work has been to analyze, in the tradition of the CPI, a few of the latter issues as a guideline for the design and operation of future high-rise structures. Our analysis has differed from the prior ones primarily by virtue of a greater focus on chemical processes. The first and most important finding from our analysis is that the twin towers might not have collapsed had it not been for the further weakening of the steel trusses by the subsequent combustion of the flammable contents of the building, and in particular of the nylon carpeting. Secondly, that combustion of the building components may have heated the floor above to the point that the carpeting ignited. Thirdly, unburned jet fuel may have flowed to floors below the point of impact through the elevator shaft, thereby spreading the fire downward. Fourthly, the combustion of both the jet-fuel and the building contents undoubtedly occurred with less than the stoichiometric amount of air and thereby produced large quantities of CO as well as other toxic materials. Fifthly, not only were the wiring and piping in the annular space surrounding the buildings rendered inoperative by the impacts and primary explosions, that open space became a channel for upward buoyant flow at high velocity. The obvious recommendations for future high-rise buildings, whatever their purpose, are to avoid flammable floor coverings, to incorporate a barrier for the downflow of spilled liquids, to provide CO-masks and/or isolated and ventilated safe-rooms on each floor, to avoid the presence of open upward channels, and to avoid windows that are easily blown out and thereby provide openings into such vertical channels. The provision of escape routes and of shielded spaces for wiring and piping were addressed in the NIST report. The analyses that led to these findings and recommendations will be described in the oral presentation and will be presented in even more detail in the complete manuscript.