http://www.thewrap.com/kiefer-sutherland-reveals-origins-of-jack-bauers-24-catchphrase-damn-it-video/

“We never meant it to catch on like it did,” says Sutherland, noting that it was initially used as a quick way to move his character on to the next scene.
Read more at http://www.hitfix.com/tv-tattle#uzdAOlLQQOlGeU5p.99