The North Tower of the WTC suffers a fire on its 104th floor. This is the 15th and last of what the National Institute of Standards and Technology later describes as “significant fires,” which occurred in the Twin Towers from 1975 onwards, and prior to 9/11. These fires each activate up to three sprinklers but are confined to just one floor. [Kuligowski, Evans, and Peacock, 9/2005, pp. 7-11]