I was working for a major insurance company at the time down in Southern England.
September tends to be a more quiet time in the Insurance trade (being on the other side of the spectrum from the hectic end of financial year, where activity becomes chaotic) so it was a rather slow paced day.
The first indication we had that something out of the ordinary was happening just after the lunch break.
They had a large communications centre on the top floor which passed financial information to all the different IFAs and department heads and in the middle of an uncharacteristic flurry of trading chaos they had briefly lost the feed to NY and the IT people were trying to figure out if this was an internal computer problem.
Our group manager who used to work on the IT team was one of the few people to have an external internet feed (dial up remember) and he was the one who passed on the news which he uncovered while trying to figure out the problem upstairs.
Initially there was some confusion as to if it was a bomb or an accidental fire because all we see was the smoke coming from the building (still pictures were all we were getting back then) and people couldn't make out any information about what had started it because we were not able to have the sound on (it had been disabled to reduce office noise). We all remembered the earlier bomb so many of us assumed this was a second attempt.
It then became a morbid game of Chinese whispers as the day progressed, as people clustered close to the internet machines would pass on updates via the internal message boards which sometimes got distorted.
By the time the Pentagon impact was announced stories of planes flying into buildings all over the world were being spread around the building.
Some of our office workers were sincerely expressing worry about being in an office building and many of our workers had friends and former colleagues who worked in the towers and were obviously distressed.
By the time I had got onto the train (filled with office workers passing information down the carriage from radio) and got home the scale of the attack became clear.
The towers became almost like a pair of prayer candles (a side effect of the abstract simplicity of the tower design), it went beyond any morbid fascination or rubber-necking.
It was more like people were willing those fire crews and office workers to safety which made the collapse of the towers all the more terrible.
I had been up to the top of South Tower in the early nineties and my memory of the height and sway of those majestic buildings and the shear scale of them (coupled with working in an office block myself) really brought the plight of the victims home to me.
We had been brought up with stories of the Blitz (the 70th anniversary of which is round the same time as this 9th) and we were very familiar through IRA attacks with acts of terrorism but the Blitz was almost mythical (being passed down from our grandparents) and the IRA attacks though frequent and horrific were not on the same scale. 9/11, was in terms of lives lost two IRA campaigns on one shocking day.