The scale was devised by Richard Binzel a professor of Earth, Atmospheric and Planetary Sciences at MIT. After five years of work the Torino scale was officially endorsed by the IAU on Thursday July 22nd 1999 at the United Nations' UNISPACE III conference in Vienna, Austria. The first version of the scale was callled "A Near-Earth Object Hazard Index" and was presented at a United Nations conference in 1995; a revised version of the "Hazard Index" was then presented in June 1999 at an IAU worshop in the Italian city of Torino. The participants voted to adopt the revised version, naming it "The Torino Impact Hazard Scale" to recognise the international cooperation at the conference.
Asked by the BBC why he decided to create the scale Professor Binzel said:
"Scientists haven't done a very good job of communicating to the public the relative danger of collision with an asteroid," he said. "Scientist-astronomers who are going to be confronted with this should have some means of clearly communicating about it so as to clearly inform but not confuse or unnecessarily alarm the public."
As a side note no asteroid identified to date has ever made it out of the green zone by having a scale value greater than one.
Resources
Professor Binzel's Homepage : http://www-eaps.mit.edu/faculty/binzel.htm
The BBC's report on the Torino scale : http://news.bbc.co.uk/1/hi/sci/tech/401777.stm
An MIT page on Binzel's research : http://web.mit.edu/giving/spectrum/fall99/briefs.html
A NASA page reporting the scale : http://neo.jpl.nasa.gov/news/news042.html