After the jets hit, stairwells became the sole means of escape for thousands of WTC occupants. But design choices hampered full evacuation -- and made the descent even more harrowing. The stairs in the twin towers were a product of their times. In 1968, as construction on the towers was beginning, New York City issued a brand-new building code, allowing for substantial reductions in egress capacity from the previous code dating to 1938. It appears that the buildings' owner, the New York Port Authority took advantage of this fact, providing only three stairwells in the center core of each tower, instead of the six that would have been required under the older code.