| No hazard (white) |
| 0 | The likelihood of a collision is zero, or is so low as to be effectively zero. Also applies to small objects such as meteors and bodies that burn up in the atmosphere as well as infrequent meteorite falls that rarely cause damage. |
| Normal (green) |
| 1 | A routine discovery in which a pass near Earth is predicted that poses no unusual level of danger. Current calculations show a collision is extremely unlikely with no cause for public attention or public concern. New telescopic observations very likely will lead to reassignment to Level 0. |
| Meriting attention by astronomers (yellow) |
| 2 | A discovery, which may become routine with expanded searches, of an object making a somewhat close but not highly unusual pass near Earth. While meriting attention by astronomers, there is no cause for public attention or public concern as an actual collision is still very unlikely. New telescopic observations very likely will lead to reassignment to Level 0. |
| 3 | A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of localized destruction. Most likely, new telescopic observations will lead to reassignment to Level 0. Attention by public and by public officials is merited if the encounter is less than 10 years away. |
| 4 | A close encounter, meriting attention by astronomers. Current calculations give a 1% or greater chance of collision capable of regional devastation. Most likely, new telescopic observations will lead to reassignment to Level 0. Attention by public and by public officials is merited if the encounter is less than 10 years away. |
| Threatening (orange) |
| 5 | A close encounter posing a serious, but still uncertain threat of regional devastation. Even though most objects of this level will be lowered to Level 0, critical attention by astronomers is still needed to determine conclusively whether a collision will occur. If the encounter is less than 10 years away, governmental contingency planning may be warranted. |
| 6 | A close encounter by a large object posing a serious but still uncertain threat of a global catastrophe. Critical attention by astronomers is needed to determine conclusively whether a collision will occur. If the encounter is less than 30 years away, governmental contingency planning may be warranted. Some objects of this level may be lowered to Level 1 or 2, if the chances of collision decrease. |
| 7 | A very close encounter by a large object which, if occurring over the next 100 years, poses an unprecedented but still uncertain threat of a global catastrophe. For such a threat, international contingency planning is warranted, especially to determine urgently and conclusively whether a collision will occur. |
| Certain collisions (red) |
| 8 | A collision is certain, capable of causing localized destruction for an impact over land or possibly a tsunami if close offshore. Such events occur on average between once a century and once per 10,000 years. |
| 9 | A collision is certain, capable of causing unprecedented regional devastation for a land impact or the threat of a major tsunami for an ocean impact. Such events occur on average between once per 10,000 years and once per few hundred thousand years. |
| 10 | A collision is certain, capable of causing global catastrophes that may threaten the future of civilization and life as we know it. Oceanic impacts can cause tsunamis hundreds, or even thousands, of feet high while land impacts can cause major firestorms. Such events occur on average once every few hundred thousand years. Larger objects of this size may strike less often. |
