The footage was filmed by two French brothers, who coincidentally had been given permission to follow and film a firefighter in his first six months on the job at a fire station near the World Trade Centre. They began filming in June.
The documentary is said to contain no gruesome images, as the brothers said they practised self-censorship. However, shots of inside the North Tower, where the fire department set up a command centre, will be broadcast, as will the image of the aircraft crashing into the first tower.
The programme has been met with fierce opposition from some victims' groups and fire fighters who think the timing of the broadcast -- which will air on Sunday, the day before the six-month anniversary of the tragedy -- is insensitive.
CBS has defended the decision, saying it is newsworthy and historically important. The network has also gone to great lengths to show it is not profiting from the broadcast, with only public service announcements and no paid-for ads being shown during the breaks.
The brothers who filmed the documentary are said to be donating any proceeds from documentary to the Uniformed Firefighters' Association scholarship fund.
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