This section provides information about the distribution, storage and effect of iodine tablets and about what you should do if a serious incident involving a nuclear power plant occurs.

You can download a PDF document containing all the questions and answers.

What to do if an incident occurs

If an incident occurs, the authorities alert the affected population by means of sirens sounding the general alarm signal. This alarm means that you must listen to the radio, follow the instructions issued by the authorities and inform your neighbours. The authorities use radio (and other media) to inform the population and issue instructions about what people should do.

It is not necessary to take iodine tablets immediately. Radioactivity is measured over a very wide area and the authorities only instruct the population to take iodine tablets in municipalities that are likely to be affected by radioactivity.

You can find further information about alarm situations here.

You should note that a siren test is carried out once a year – on the first Wednesday in February. This is a good time to check whether you have enough iodine tablets at home.

The authorities use radio and other media to order measures designed to protect the population as well as possible against potential radioactivity leaks.

The most important thing to do is to avoid being outdoors; you should go into a building, close the windows and doors and turn off all ventilation systems. This prevents air contaminated with radioactivity from entering the building. It is vital to follow the authorities’ instructions if such a situation occurs.

Another measure that may be ordered is to either ready or – in municipalities in which increased levels of radioactivity are likely – take iodine tablets.

The thyroid gland is protected by the administration of non-radioactive iodine if the tablets are taken within a few hours prior to the danger posed by radioactive iodine occurring or, if this is not possible, as soon as possible during the first few hours afterwards. If the tablets are taken too early they lose their protective effect. It is therefore very important to follow the authorities’ instructions and to take the tablets at the exact time the order is given. In addition, taking iodine tablets does not protect the body against the harmful effects of other radioactive elements (e.g. caesium, strontium) which may escape into the environment if a serious incident occurs at a nuclear power plant. The authorities will therefore always order other protective measures in addition to taking iodine tablets, e.g. staying at home or in the basement or evacuation of the affected population.

When radioactivity is leaked, the authorities use various parameters (radiation intensity, wind speed, wind direction, etc.) to determine exactly which municipalities will be put at risk by radioactivity. They order appropriate measures to protect the population in these municipalities. One of these measures may be the administration of iodine tablets.

If an incident occurs, the authorities will communicate the protective measures that must be taken. You should turn on the radio or consult other media in all cases and follow the instructions given by the authorities. The affected population will usually be ordered to go inside a building and to shut the windows and doors. The authorities will also say how long people must stay inside the building or for how long they should not leave the building under any circumstances.

No, that isn't necessary. Iodine tablets are also distributed to all workplaces and public facilities within 50 km of the nuclear power plants in Switzerland.