It is a scale designed by IAU in 1999, that evaluates the risk of any potential asteroid impacts in near future (up to a 100 years) and signs them the specific number (on a scale of 0-10) and color code, relating to its intensity. Its primary focus is to facilitate government response to impending doom (Don’t worry nothing has gone beyond 2 in this scale) and to make people aware of the steps they have to take. Now we will briefly see what different levels mean on this scale along with their color codes.

Normal(0): Near 0 chance of collision or no notable effect in any such event. Also includes celestial objects that burn in atmosphere.

Meriting Attention

(1): Not a threat but has a chance to pass very close to the earth. In most cases further observations re-assign, them to level 0. Tunguska impact falls here.

(2 & 3): They have an impact chance of greater than 1%. They may account for localized and regional destruction respectively. However only one asteroid has been detected in this range and was later classified to level 0. Official attention is sought if collision is bound to happen in a decade.

Threatening

(4, 5 & 6): A close encounter with a large object is seriously possible, and may lead to regional or global devastation. Immediate action to discern the possibility of impact is required. Official attention is necessary to minimize the loss of life and property.

However scary may category 4,5,6 seem, it won’t be enough to end civilization on a whole. This category asteroids have a very slight chance of triggering an impact winter (Winter that happens when asteroid impact causes dust to block sunlight. The Chixclub impactor (the asteroid that killed dinosaurs) was a category 5 asteroid according to today’s scales.

Certain Collisions or catastrophic (We haven’t found or detected anything of this sort)

(8 & 9): A collision is imminent and the results would be catastrophic on a regional and global level repectively, including earthquake, tsunamis and impact winters. The chance for level 8 event is on average between once per 50 years and once per several 1000 years.

(10): It deserves a special mention of its own right. Irrespective of where it lands, it will trigger a global climatic emergency and may pose a threat to entire life on planet. These events occur once in 100,000 years or less, but there is no detected evidence of such events so we can relax for a while.

On a side note, there is an unofficial level that I personally would want to see in this scale, which I call level Z, and it would encompass the events like the one that led to the formation of our moon. But then they would, if we consider our theories about moon formation to be true, will be classified as on an inter-planetary collision hazard scale, which is a topic for future. Know more about the Torino Impact Hazard scale: https://cneos.jpl.nasa.gov/sentry/torino_scale.html

Another similar scale: Palermo Technical Impact Hazard Scale