Office Fires Don't Burn Hot Enough?

Just caught this little aside in the book, 102 Minutes, the Untold Story of the Fight to Survive Inside the Twin Towers, on page 67:

"By that time, the Towers had already opened, and small fires set by an arsonist in February 1975 had caused parts of floors to buckle."

Well, that certainly attracted my attention and I did some web-checking. The 9-11 Timeline covers this with a little more detail:

Additionally, on February 14, 1975 a major fire occurred, the result of arson, which began on the 11th floor of the North Tower during the middle of the night. Spreading through floor openings in the utility closets, it caused damage from the 10th to 19th floors, though this was generally confined to the utility closets. However, on the 11th floor about 9,000 square feet was damaged. This was about 21 percent of the floor’s total area (43,200 square feet) and took weeks to repair. Some parts of the steel trusses (floor supports) buckled due to the heat.

Steel trusses buckled due to heat? You don't say!