Dirty bomb

A dirty bomb is a conventional explosive that is set off to carry radioactive substance into the environment. A dirty bomb is not the same as a nuclear weapon or a nuclear explosion. The explosion itself and its consequences would be more dangerous to humans than the radioactivity contained in the bomb. However, radiation increases fear, which is why it can be considered, above all, as an instrument of terrorism.

A dirty bomb can contaminate an area over a radius of a few kilometres so that the area needs to be cleaned.

People closest to the explosion are the most susceptible to personal injuries in the same way as in any other explosion. The harmful effects of radiation on health are likely to be minimal.

They depend on:

• the size, power and spreading method of the explosive itself; and
• the quantity and characteristics of the radioactive material used (e.g. half-life).

The radioactive material spreading into the environment can be liquid, powder or solid material.

All of these factors, as well as weather conditions, affect possible protective measures and the aftercare of the situation.

Health and other effects

It is difficult to build a dirty bomb that would cause direct health effects through radiation exposure. Exposure to the radioactivity of a dirty bomb can endanger health in the same way as any other source of radiation.

The health effects of radiation are proportional to the radiation dose received. Radiation exposure is significantly affected by the following:

• Exposure time: a shorter exposure time reduces the radiation dose.
• Method of exposure: External exposure to a dirty bomb is unlikely to cause a significant radiation dose. However, the direct handling of the radiating parts of a radioactive bomb, or the introduction of such a part into the body, can quickly cause a significant radiation dose. It can also be dangerous for a dirty bomb's radioactive substance to enter the body by ingestion or inhalation.
• Type of radiation (gamma, beta, alpha): Gamma radiation is penetrating and causes radiation exposure even farther away from the radiating material. Beta and alpha radiation stops after a short journey through the air. Alpha and beta emitters cause radiation exposure, especially when the emitting substance is on the skin or inside the body.
• The person's distance from the radiation source: the intensity of the radiation decreases when moving away from the radiation source.

A radiation dose indicates the health detriment caused by radiation. The unit of dose is the sievert (Sv). Any radiation exposure and radiation dose can increase the statistical risk of developing cancer, although there are many other factors that affect the development of cancer in addition to radiation. Examples of radiation doses can be found on the Preventing health effects of radiation page of the Radiation and Nuclear Safety Authority.

Harmful effects of radiation can occur after a long period of time. Radiation exposure caused by a dirty bomb is unlikely to increase the risk of cancer in exposed people to such an extent that this would be statistically detectable.

The detonation of a dirty bomb would have significant social and economic consequences in addition to health risks. If the contaminated area had to be closed for cleaning and the people living there evacuated, it could be costly and time-consuming to making the environment habitable.

Protective measures

If an explosive has proven to be a dirty bomb, the police and rescue authorities are responsible for the actual rescue measures, and the Radiation and Nuclear Safety Authority will issue recommendations related to radiation safety. The protective measures after a dirty bomb has exploded are guided by three basic radiation safety factors:

• Minimize the duration of exposure to radiation.
• Stay at a sufficient distance from the radiation source.
• Ensuring physical protection, which can also prevent the entry of radioactive substances into the body by inhalation.

Since the shrapnel from the bomb in the vicinity of the explosion site may contain radioactive substances, it should not be picked up. In practice, the affected population is advised to follow the instructions of the authorities and to act accordingly.

A dirty bomb is difficult to build

A dirty bomb is an “ordinary explosive” to which a radioactive substance with suitable radiation properties and half-life is added. For example, if the half-life is short, the activity level of the radiation produced by a dirty bomb decreases rapidly and the radiation effects remain minor. If, on the other hand, the radioactive substance used is highly radiative and the half-life is long, the effects are correspondingly larger and longer-lasting.

In practice, however, it is difficult to build a dirty bomb. It requires not only explosives but also the acquisition of radioactive substances. Although radioactive substances are widely used in medical care and industry, for example, the use of radiation sources and radioactive materials is strictly controlled. The Radiation and Nuclear Safety Authority supervises their use in Finland and carries out regular inspections at places where radiation is used.

The handling of a radioactive substance to make a bomb may expose the person who built the bomb to radiation.

Illegal import of a radioactive substance requires planning and information in order to avoid being caught.

Protection in case of an explosion

In the event of an explosion, it may not be immediately known that radioactive substances were involved in the explosion. Instructions on how to act when radioactive exposure is suspected or known to have occurred are listed below.

If you are outside and near the accident site:

• Cover your nose and mouth with a cloth to reduce the risk of breathing in radioactive dust or smoke.
• Do not touch anything in the explosion area.
• Immediately go inside a building with intact walls and windows. This protects you against radiation.
• When indoors, do not wear the piece of clothing that you used as a respiration protector, and remove the outer layer of your clothes. Put these potentially radioactive clothes and shoes in a plastic bag or isolate them by other means, if possible. In this way, you will get rid of most of the radioactive dust.
• Put the plastic bag in a place where others can't touch it, and wait until the authorities tell you what to do with it.
• If possible, take a shower or wash yourself with soap and water. Also wash your hair. This removes the remaining dust.
• Follow the media and wait calmly for instructions.

If you are inside a building near the accident site:

• If the windows and walls are intact, do not leave and stay inside.
• To prevent radioactive dust from entering the interior, close all windows and exterior doors – including fireplaces and possible air conditioning. There is no need to tape the windows and doors.
• If windows or doors are broken, go inside a room with intact walls and windows, and stay inside.
• If the building is badly damaged, immediately move inside a nearby building that is intact. If you have to go outside, cover your nose and mouth with a piece of clothing. When indoors, do not wear the piece of clothing that you used as a respiration protector, and remove the outer layer of your clothes. Put these potentially radioactive clothes and shoes in a plastic bag and in a place where others can't touch them, and wait until the authorities tell you what to do with them. If possible, take a shower or wash yourself with soap and water. Also wash your hair.
• Follow the media and wait calmly for instructions.

If you are in a vehicle or other means of transport in the event of an accident:

• Close the windows, air conditioning and any ventilation valves. Cover your nose and mouth with a piece of clothing to prevent radioactivity from entering your body by inhalation.
• If you are near your home, office or a public building and the building is intact, safely move inside.
• If you cannot safely enter a building, drive to the side of the road and, if possible, into shadow or under shelter. Turn off the engine, listen to the media, and wait calmly for instructions. Stay in the car until you are instructed to move on.

Using your phone:

• Avoid using the phone during a potential radiation hazard. An excessive load on call connections can prevent all calls from reaching their destination, which may make rescue operations more difficult.

Protecting your pet:

• If you have pets outside, bring them inside as soon as possible, where you can remove any dust before it spreads, and where you can wash them thoroughly with soap and water.

After the explosion:

• Do not try to return or go to the explosion site. Keep following the media.
• The authorities will advise on any additional protective measures, evacuations, and so on.