"Please explain your understanding of pressure relief valves on high pressure systems and what they do. Please explain why they are vital to ensure that things that are not over pressurised do not damage the equipment."
Yes they do, but not in a SEALED enviroment (like the WTC). They have valves that allow the pressure to be reduced, the WTC was not a "valve" for pressure. The bulding was HERMETICALLY sealed. Therefore, the air would had to of gone through the path of LEAST resistance, which was the shafts. The elevator doors were closed. What blew them and then created a small pin point hole in only a few windows???? If there was that much pressure, a large portion would have blown. PHYSICS escapes you again??? The "air" would not have ended up 20 floors below, it would be in several floors below the collapse where the GREATEST pressure would be.
"You being an engineer will have no problem with this."
I have no problem with this, but you seem to have a problem understanding that with pressure, it would have blown out more windows rather than just a small pin hole for the air to escape.
"Ps Relief valves= windows (a clue)"
Apparently not for you.