Anyway the seams between the plastic sheets sometimes intercepted the corner of an envelope. In a building as tall as the WTC mail would hit impressive speeds. So one jammed letter would quickly gather many letters, traveling near the speed of sound, into a densely packed arterial blockage ... Guess who found them?
Splunge recounts his adventures as an "ex-officio mail plumber" valiantly clearing clogs in the WTC mail chutes in Ragini's fun post, The mail chutes of New York City