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Ionising radiation

Environmental Radioactivity - Medicine - Occupational Radiation Protection - Nuclear Hazards Defence

Ionisierende Strahlung

Phases of an emergency

  • Each single phase of a radiological emergency requires different countermeasures to protect man and environment against its consequences.
  • Basically, one differentiates between urgent the response phase (during an accident or emergency) and the transitional phase (after radioactivity has been released).

5 Phases

A radiological emergency cannot only be divided into possible scenarios but also into the possible incident phases consisting of

  • Uncertain Situation
  • Hazardous Phase
  • Release / Exposure Phase
  • Transitional Phase (phase after the accident / incident)
  • Long-Term Transitional Phase.

Each single phase requires different countermeasures to protect man and environment against the consequences of the radiological emergency.

The five phases can be divided into 2 main phases: The Urgent Response Phase and the Transitional Phase.

Urgent Response Phase

All phases occurring during the accident or incident are allocated to the Urgent Response Phase. Generally they occur within few hours and days. If required, early protective measures are taken during this phase, such as the administration of iodine tablets, requesting the public to stay indoors (sheltering) or evacuation.

Phase 1: Uncertain Situationshow / hide

In the event of a radiological emergency, the phase "Uncertain Situation" is marked by the fact that the control of radioactive material or its safe handling cannot be guaranteed. The situation is uncertain: If the accident or incident develops in an unfavourable manner, mechanisms are lacking that can prevent exposure of man and environment to enhanced radiation. Emergency-response relevant radiation exposures do not occur during this phase – however, if the situation continues to develop in an unfavourable manner, it might not be possible to prevent an escalation effectively.

"Uncertain Situations" could be e.g. the failure of safety systems in a nuclear power plant (emergency scenario Accident in a Domestic Nuclear Power Plant) or damage to the outer packaging during the transport of a radioactive source (emergency scenario Transport Accident).

Phase 2: Hazardous Phaseshow / hide

During the Hazardous Phase man and environment are not exposed to enhanced radiation, either – no radiation exposure has occurred as yet. However, if no measures are taken, emergency-response relevant radiation exposures will occur during this phase. Already during this phase processes are effective that cause an impermissible radiation exposure unless countermeasures are taken.

Examples of a Hazardous Phase would be that the cooling of the reactor core in a nuclear power plant cannot be guaranteed (emergency scenario Accident in a Domestic Nuclear Power Plant) or that the transport container catches fire during the transport of a radioactive source (emergency scenario Transport Accident).

Phase 3: Release Phase (Exposure Phase)show / hide

During the Release Phase radioactivity is released into the environment. Persons potentially at risk can be protected against radiation exposure by different measures such as sheltering or administration of iodine tablets. During this phase of a radiological emergency, processes are effective that cause an enhanced radiation exposure to persons unless countermeasures ensure that they protect themselves by their own behaviour.

A Release Phase (Exposure Phase), for example, would be the release of radioactivity into the atmosphere after a core melt-down during an accident in a nuclear power plant (emergency scenario Accident in a Domestic Nuclear Power Plant) or the release of radioactivity from burning containers after a transport accident (emergency scenario Transport Accident).

Transitional Phase

All phases are allocated to the Transitional Phase that occur after radioactivity has been released. It comprises the review of earlier protective measures and the preparation of long-term measures and aims at rehabilitating the conditions of human life. This phase may last for several weeks up to several decades.

Phase 4: Transitional Phaseshow / hide

During the Transitional Phase, the exposure situation has already occurred. Persons have been exposed to enhanced radiation levels. Protective measures are now required to end or reduce the enhanced radiation exposure to the (potentially) affected persons to limit the number of persons affected by radiation exposure.

During the Transitional Phase the environment is radioactively contaminated after release of radioactivity has stopped, e.g. from a nuclear power plant (emergency scenario Accident in a Domestic Nuclear Power Plant) or from a transport container (emergency scenario Transport Accident). Depending on the emergency scenario, this phase may last for days, weeks or months.

Phase 5: Long-Term Transitional Phaseshow / hide


During the long-term transitional phase, an accurate picture of the exposure situation is available: It is known what radioactive nuclides have been released and to what extent they have been distributed where. It is now also known what areas are radioactively contaminated for the long term as a result of the release of radioactivity.

One example for the Long-Term Transitional Phase would be the long-term contamination of buildings after a serious accident in a nuclear power plant (emergency scenario Accident in a Domestic Nuclear Power Plant). Depending on the level of contamination, this phase may for some areas last for several years or decades after the accident.

State of 2018.07.23

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