Radiological and Nuclear Emergencies

A nuclear or radiological emergency is an event that has led, or could lead, to a radiological threat to public health and safety, property, or the environment.

Nuclear or radiological emergencies that could affect Canadians include:

  • an emergency at a nuclear facility, such as a nuclear power station, in Canada, in the United States, or abroad;
  • an emergency involving a nuclear-powered vessel in a Canadian port;
  • a transportation accident involving the shipment of radioactive material;
  • an emergency involving the loss, theft, or discovery of radioactive material;
  • a terrorist attack utilizing radioactive materials, such as a "dirty bomb"; or
  • other events involving the uncontrolled release of radioactivity or radioactive material, such as the 1978 crash in the Northwest Territories of COSMOS 954, a Soviet nuclear-powered satellite.

In Canada, every level of government has responsibility in the event of a nuclear or radiological emergency. Response begins at the local or municipal level, and progresses to the provincial and federal levels, depending upon the location, type, and size of the emergency. As a signatory country on two international emergency conventions under the International Atomic Energy Agency (IAEA), Canada also has a responsibility to notify other countries if it has had a nuclear emergency, and to assist other countries with their own emergency response to a nuclear emergency if requested to do so.

The International Nuclear Event Scale

The International Nuclear Event Scale (INES) was developed by the International Atomic Energy Agency (IAEA) and the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-Operation and Development (OECD) in order to communicate the magnitude and safety significance of nuclear emergencies between countries around the world, including Canada.

According to the INES system, a nuclear emergency is classified on the scale at one of seven levels. In general, the higher the classification level, the greater and more widespread is the safety significance. The categories are grouped as follows:

  • Level 0/below scale: emergencies with no safety significance (which means that the emergency has no actual, or potential for degradation of safety systems of the facility);
  • Levels 1 to 3: emergencies of significance for workers at the emergency site but not for the public; and
  • Levels 4 to 7: emergencies with significance for workers and the public.

Graphic of the International Nuclear Event Scale:

The International Nuclear Event Scale ranks the severity of a nuclear event by assigning a number between 0 and 7. Deviation level is assigned a 0 and is below scale / no safety significance. This means that the emergency has no actual, or potential for degradation of safety systems of the facility.

The Incident levels include

  • 1: Anomaly,
  • 2: Incident and
  • 3: Serious incident.

The Accident levels include

  • 4: Accident without significant off-site risk,
  • 5: Accident with off-site risk,
  • 6: Serious accident and
  • 7: major accident.

Nuclear Event Scale

The 1986 accident at the Chernobyl nuclear power plant is classified as level 7 on the INES scale. The 1979 accident at Three Mile Island is classified as level 5.

Classifying a Nuclear Emergency:

The Canadian Nuclear Safety Commission, in consultation with the company affected, sets the INES level for emergencies in Canada. The level will not be available immediately when the emergency occurs because it takes time to collect and review all of the necessary information. It is also possible that with further information, the emergency level may change. For example, while an emergency might initially be classified as low on the INES scale, subsequent complications may result in an INES classification to a higher level.

Emergencies are not classified on the INES scale if they are not of nuclear or radiological significance. For example, a fire at a nuclear power station is not classified if it does not involve radiological material. The INES classification should not be confused with emergency classification systems used at nuclear facilities to tell staff and local authorities what to do in response to an emergency.

Examples of Past Nuclear/Radiological Emergencies


On 24 January 1978, COSMOS 954, a Soviet nuclear-powered surveillance satellite, crashed in the Northwest Territories. The crash scattered an enormous amount of radioactivity over a 124,000 square kilometre area in Canada's north, stretching southward from Great Slave Lake into northern Alberta and Saskatchewan.

The clean-up operation was a coordinated event between the United States and Canada. Dubbed "Operation Morning Light", the clean-up effort continued into October 1978 and resulted, according to the Atomic Energy Control Board (now the Canadian Nuclear Safety Commission) , in the estimated recovery of about 0.1 percent of COSMOS 954's power source.

The crash of COSMOS 954 raised international policy questions. Soon after the satellite's crash, there was a call from the United States to prohibit satellites containing radioactive material from orbiting the earth. This was followed by similar calls from Canada and countries in Europe. In November 1978, the United Nations authorized its Committee on the Peaceful Uses of Outer Space to set up a working group to study nuclear-powered satellites.

Three Mile Island:

On 28 March 1979, there was an accident at the Three Mile Island nuclear power station near Harrisburg, Pennsylvania. There were no injuries or adverse health effects to the public from this accident. Although some radioactive gas was released a couple of days after the accident, it was not enough to cause any dose above regular background levels to local residents. However, conflicting information released during the event exacerbated the public's fears, highlighting the need for a consistent and coherent public information and emergency communication strategy.

The accident also highlighted the need for both national and international plans to handle a peacetime nuclear emergency.


On 26 April 1986 the world's most severe nuclear reactor accident occurred in Chernobyl, Ukraine (at that time part of the Soviet Union). An area of about 5 million hectares - almost the size of Nova Scotia - was contaminated and 160,000 people had to be permanently evacuated. Radioactive material affected not only the Ukraine but also neighbouring countries and parts of Western Europe.

The Chernobyl accident demonstrated the need to include the possibility of trans-boundary implications in national emergency plans. The concern that any country could be affected not only by nuclear accidents occurring within its own territory but also by the consequences of accidents happening abroad, stimulated the establishment of national emergency plans in several countries. Also, the trans-boundary nature of the contamination resulting from the Chernobyl accident prompted international organizations to promote international cooperation and communication, to harmonize actions, and to develop international emergency exercises such as the Nuclear Energy Agency's INEX series. The international community reached agreements on early notification in the event of a radiological accident and on assistance in radiological emergencies through international conventions developed by the International Atomic Energy Agency.


On March 11, 2011 a magnitude 9.0 earthquake struck off the coast of Japan. This triggered a tsunami which struck Japan’s east coast causing great damage to the Fukushima Daiichi nuclear power plant. The plant was severely affected by the tsunami and a nuclear emergency was declared by Japanese authorities. Residents were evacuated from the area surrounding the Fukushima Daiichi nuclear power plant. In the weeks and months following, Japanese authorities worked to bring the situation under control. In Canada, various federal and provincial departments and agencies worked to monitor the situation and offer assistance to Japan. Radiation levels resulting from this nuclear accident were, and continue to be, of no public health concern for Canadians. Internationally, an Action Plan on Nuclear Safety was developed under the IAEA to strengthen nuclear safety worldwide, including nuclear emergency preparedness and response.

Report a problem or mistake on this page
Please select all that apply:

Privacy statement

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: