THE US: September 11th 2001 was like no other day in US history. The trauma of watching people die - in real time on television - following the attacks on the World Trade Centre in New York was deeply penetrating. Conor O'Clery, in New York, reports
In the aftermath, about 90 per cent of Americans reported some symptoms of stress, and 40 per cent severe stress, according to a survey conducted at the University of Chicago.
Now psychologists and scientists are worried that a flood of new television documentaries, relentless playing of horrific images of death and destruction, along with countless memorial services on Wednesday, planned to mark the first anniversary of the attacks, will again impact on those most affected by the tragedy.
A study of Manhattan residents by a group at the New York Academy of Medicine concluded that those directly affected by the attacks who frequently watched images of "people falling or jumping from the towers" were more likely to report symptoms associated with post traumatic stress disorder (PTSD).
The distress symptoms include loss of sleep and appetite, increased consumption of alcohol and tobacco and heightened feelings of anxiety.
They are most likely to be felt by those who lost a relative or friend or co-worker in the attacks, estimated at 10 million Americans by psychologists at the Research Triangle Institute in North Carolina.
"You have got about two million of those people in New York, another 500,000 in the Washington area and another seven million plus around the country," psychologist Mr William Schlenger of the institute told the Washington Post. Based on the survey, he estimates half a million people in the New York area may have developed the disorder.
The team found that the more often people who reported symptoms of PTSD in New York watched television images of the attacks, the more likely they were to suffer increased psychological impact.
On a positive note, psychologists hope the commemorations will help bring closure for many distressed Americans. But there will be no avoiding stark reminders of the day that profoundly shocked the country.
Ninety hours of new and repeat footage of the destruction of the twin towers are scheduled for television documentaries with titles such as "America Remembers". Up to 150 books about September 11th will flood the book stores.
Memorial services, concerts, requiems, exhibitions of photographs and art work, and candle-lit vigils are planned for every city, town and borough.
Last night a silent, one-mile procession of police officers, firefighters and rescue workers, each carrying a poster with a victim's name, walked to a service and vigil at Bay Ridge, Brooklyn.
Yesterday, second World War planes flew low in salute over Ground Zero, where preparations are being finalised for the main memorial ceremonies on Wednesday morning.
Mayor Michael Bloomberg will call four times for a moment of silence at the precise times the hijacked planes impacted the twin towers, and crashed into the Pentagon and in Pennsylvania. New York Governor Mr George Pataki will read the Gettysburg Address and former Mayor Rudolph Giuliani will begin reading the names of the dead. Relatives bearing flowers will then for the first time be allowed to descend the ramp into the pit from which debris has been cleared. Church bells will ring at 10.29 a.m. to mark the fall of the second tower.
The ceremonies will begin at 1.00 a.m. with bagpipe and drum processions from each of the five New York boroughs to the World Trade Centre site.
The number of victims at ground zero is currently put at 2,654 plus 87 on American Flight 11 and 60 on United Flight 175. There were 125 victims at the Pentagon and 59 on American Flight 77, which struck the building.
Over the weekend convoys of bikers flying the Stars and Stripes converged on the site in Pennsylvania where 40 passengers and crew died after a struggle with the hijackers.
An observation platform has been erected there to accommodate the number of people making pilgrimage to honour the victims.
Among hundreds of events in New York these will be a series of discussions at City University on "death, bereavement and mourning" for those seeking to understand the effect of the attacks on the national psyche.
A three-day marathon of 50 plays, monologues and songs called "Brave New World" will be performed by some 70 actors including Sigourney Weaver and Eli Wallach at Town Hall. Some of this week's commemorations have a real New York flavour. The Brooklyn Academy of Music will show Woody Allen's movie Manhattan at the Rose Cinema, without charge.
Among the memorial services yesterday was a special programme at the Islamic Centre of Long Island.