Using a cubicle based on the offices of insurance firm Marsh & McLennan - a north tower tenant that lost 295 employees - federal fire experts conclude it was more likely the heat of burning office materials brought down the tower, rather than jet-fuel-fed flames.

This test, conducted by National Institute of Standards and Technology last month, showed the fuel from the plane that crashed into the tower burned out quickly - but the fire it created grew in intensity by up to another 300 degrees as it consumed office products and structures.

The computers, cubicle walls, furniture, files and paper - recreated on detailed information supplied by the insurance company on the exact materials used in their offices - blazed at temperatures that reached 1,200 degrees, the NIST test found.

The test fire burned for 33 minutes before the 386 pounds of material were consumed and reduced mostly to ash and gases.