International Nuclear Event Scale

The **International Nuclear Event Scale** (INES) is a system introduced by the International Atomic Energy Agency (IAEA). It was introduced  to allow people to communicate how serious a nuclear accident is. Other people are then able to react faster  to take protection measures. For each level, there is a list of things that must be there, for the accident to be of that level.

There are 7 levels on the INES scale:

<div style="width: 17em; height: 5em; color: #000000; background-color: #FF0000;">**7**
Major accident
(maximum credible accident)</div>
   <div style="width: 18em; height: 3em; color: #000000; background-color: #FF6600;">**6**
Serious accident</div>
   <div style="width: 19em; height: 3em; color: #000000; background-color: #FF9900;">**5**
Accident with off-site risk</div>
   <div style="width: 21em; height: 3em; color: #000000; background-color: #FFCC33; border-bottom: 2px solid;">**4**
Accident without off-site risk</div>
   <div style="width: 25em; height: 3em; color: #000000; background-color: #FFFF00;">**3**
Serious incident</div>
   <div style="width: 27em; height: 3em; color: #000000; background-color: #33CC00;">**2**
Incident</div>
   <div style="width: 29em; height: 3em; color: #000000; background-color: #009900; border-bottom: 2px solid;">**1**
Anomaly</div>
   <div style="width: 33em; height: 3em; color: #FFFFFF; background-color: #006600;">**0**
Deviation, no safety relevance</div>

## Details

**Level 7** is the highest level. Accidents of this type have a large impact (pollution, radiation) outside the site where they occur. The health of many people is put in danger. There are big effects on the environment. Examples: Fukushima nuclear disaster - 2011, Chernobyl disaster (former Soviet Union) - 1986.

**Level 6** Accidents of this type have a large impact (pollution, radiation) outside the site where they occur. Several governments may need to do a lot to protect their population. Example: Mayak (former Soviet Union) 1957. Because of the levels of radioactive material<nowiki/>s released, the Mayak accident would probably be rated at level 7 today.

**Level 5** Accidents of this type release some radiation. Some groups of people which are at risk may need special countermeasures.  Examples: Windscale fire (United Kingdom) - 1957, Three Mile Island accident (United States) - 1979.

_The Levels 5-7 are related to severe damage of the reactor core and the radiological barrier<nowiki/>s._

**Level 4** is for significant damage of the reactor core / radiological barriers and/or a fatal exposure of a worker (or more), but the off-site impact is minor, resulting in public exposure of the order of the prescribed limit<nowiki/>s. Examples: Windscale (United Kingdom) - 1973, Saint-Laurent (France) - 1980, Buenos Aires (Argentina) - 1983.

**Level 3** is for very small off-site impact, although related to severe spread of contamination on-site / acute health effects to a worker (or more). It is a "near accident" event, when no safety layers are remaining. Example: Vandellos (Spain) - 1989, THORP plant Sellafield (United Kingdom) - 2005.

**Level 2** is an incident with no off-site impact, related to significant spread of contamination on-site / overexposure of a worker.

**Level 1** is an anomaly beyond the authorized operating regime.

**Level 0** is a "below-scale event" of no safety significance.

There are also events of no safety relevance, characterized as "out of scale".

## Other websites

- International Nuclear Event Scale , IAEA
- International Nuclear Event Scale, User's Manual , IAEA, 2001