Read the book 102 Minutes, by Dwyer and Flynn. Here is a review:
This book doesn't romanticise the event - it tells the story, warts and all.
For example, I thought that the collapse of the South Tower would lead to firefighters and the police immediately evacuating the North Tower. The book reveals that many of the firefighters had no idea that the South Tower had fallen - the police knew (as the police helicopters relayed the information) but on the police frequency only. Firefighters and the police used different frequencies. Cooperation between the two was poor due to longstanding rivalry.
I write coincidentally on the 10th anniversary of 9/11 (I happened to finish the book today) so there are many TV programmes on at present. The book enables me to recognise untrue stories - for example a TV programme today stated that doors accessing the roofs were locked in order to prevent suicides. Well, the book states that the doors were locked due to longstanding FDNY (Fire Department, City of New York)/police rivalry. It explains that during the 1993 bombing, a police helicopter lifted people to safety off the roof. FDNY thought that it was a publicity stunt and was dangerous as it would cause confusion in a fire, with people heading in opposite directions. So the doors were locked.
Incidentally, years ago (immediately after 9/11?) I heard a third story - the doors were locked to prevent a helicopter assault by terrorists. These three different stories show how the truth gets warped and how we cannot necessarily believe what we read even in apparently respectable newpapers or hear in TV news reports from presenters who we trust. Of course, even the story in the book could be wrong but the explanation is so detailed that it seems believable. I can imagine a reporter assuming, for example, the perfectly reasonable 'suicide prevention' story or hearing it from a person he interviewed (who didn't actually know), therefore starting an urban legend. I wonder how many other historical 'facts' are untrue.
The book reveals that people who could have escaped (as they were below the impact zone) didn't (at least at first) as 911 told them to stay put and seal the doors to prevent smoke intrusion. That was official policy, and made sense as collapse was thought impossible. In addition, many people beneath the crash zone survived the impact and should have been unable to escape but couldn't because they could not open doors. They were the sort of people that the firefighters were (in some cases) able to rescue.
Many who started to evacuate the South Tower after the North Tower was hit were persuaded to return to their offices by an announcement that it was safe to do so.
It is not necessarily true that all those that jumped did so voluntarily. Some appear to have been nudged out by the crush to escape heat and smoke.
What is particularly shocking is that a group of people evacuating the North Tower after the South Tower collapsed reported that the 19th floor was 'carpeted with firefighters...'; '...they guessed there were at least 100...'. On telling them to evacuate, someone replied "We'll come down in a few minutes" (p. 226-227, 2005 edition). It appears that they were unaware that the South Tower had collapsed or that collapse of the North Tower was imminent. Many lives were apparently lost due to poor communication.
The book reports Giuliani stating that the firefighters had received the order to leave but interpreted it as an order to evacuate civilians, not to evacuate themselves. The book rebuffs this, stating that while some firefighters heroically remained despite knowing the danger, 'numerous firefighters recalled that they were unaware of how serious the situation had become in those final minutes' (p. 251-252). The book cautions against romanticising history.
The New York Police, FDNY and many civilians willingly walked into a patently dangerous situation. I have nothing but respect for them.