What is a dirty bomb and how do you protect yourself?

Short answer. A dirty bomb, or radiological dispersal device (RDD), is a conventional explosive combined with radioactive material. It cannot create an atomic blast ¹. The U.S. Nuclear Regulatory Commission says most would not release enough radiation to kill people or cause severe illness, and that the explosion itself is more harmful than the radioactive material ². The official advice is to get inside, stay inside and stay tuned ¹⁴.

What exactly is a dirty bomb?

The CDC describes a dirty bomb as a mix of explosives and radioactive powder or pellets. When it goes off, the blast spreads radioactive material into the surrounding area ¹. The terms "dirty bomb" and "RDD" are often used interchangeably ². Strictly speaking, an RDD is any device that spreads radioactive material on purpose without a nuclear detonation, and an explosive is only one way to do it ³.

The NRC notes that radioactive materials are used routinely in hospitals, research facilities, industry and construction, for example to treat illness, sterilize equipment or inspect welds. It adds that the vast majority of these materials would not be useful in an RDD ².

A related threat is a hidden sealed source, called a radiological exposure device (RED). It exposes people nearby to radiation but does not contaminate them ³.

How is a dirty bomb different from a nuclear weapon?

They work in completely different ways. A nuclear weapon releases energy through a nuclear chain reaction. A dirty bomb is an ordinary explosion that carries radioactive material with it ³.

The NRC sums it up: a dirty bomb is not a "weapon of mass destruction" but a "weapon of mass disruption", where contamination and anxiety are the main objectives ². If you are preparing for a nuclear detonation instead, the guidance is different; see the radioactive fallout guide.

What is the actual health risk?

The CDC says the main danger comes from the explosion, not the radiation. The blast and flying fragments, some of them radioactive, can injure people nearby ¹. Only people very close to the blast would receive enough radiation to become seriously ill right away ¹.

Further away, the risk comes from radioactive dust and smoke, which can travel and harm health if it is inhaled or if people eat or drink contaminated food or water ¹. The NRC adds that radioactive material becomes less concentrated and less harmful as it spreads, and that immediate health effects from the low radiation levels expected from an RDD would likely be minimal ². Health effects rise with the dose: the amount absorbed, the type of radiation, the distance from the source, whether exposure is external or internal, and how long it lasts ².

The U.S. medical guidance used by hospitals says that while large numbers of people near a detonation might need decontamination, few if any would be contaminated enough to need medical treatment ³. Fire, smoke, shrapnel, industrial chemicals or a second device may also be present ³.

Has anything like this happened before?

An accident in Brazil, not an attack, shows what dispersed radioactive material can do. In September 1987 in Goiânia, a caesium-137 source was taken from an abandoned radiotherapy clinic, sold for scrap and broken open ⁷. According to the IAEA, about 112,000 people were monitored and 249 were found to be contaminated ⁷. Twenty were hospitalized and four of them died ⁷. More than 3,000 cubic metres of waste were removed ⁷.

This was not a bomb. The source was removed on 13 September and passed from hand to hand, and people handled the caesium powder, until a doctor recognized the symptoms of radiation overexposure on 28 September ⁷. That is very different from a dirty bomb, where emergency responders can detect radiation with equipment many of them already carry ².

What should you do if a dirty bomb goes off?

The three steps from the CDC and Ready.gov are get inside, stay inside, stay tuned ¹⁴.

1. Get inside. Move to the nearest sturdy building. Ready.gov says the safest buildings have brick or concrete walls, and underground parking garages and subways can also provide good shelter ⁴. Go to a basement or the center of the building, away from windows ⁴.
2. Stay inside. Ready.gov advises staying in the most protective location for the first 24 hours unless there is an immediate hazard such as fire or building collapse, or officials say it is safe to leave ⁴. Canada advises being prepared to shelter in place for at least 24 hours, closing doors, windows and fireplace dampers, and turning off fans and air systems that draw in outside air ⁸.
3. Stay tuned. Follow radio, TV or official alerts. Leave only when officials tell you to, and do not return to an evacuated area until they say it is safe ⁴.

If you are outside or in a damaged or smoky building, the U.S. medical response guidance (REMM) says to move immediately to the nearest robust, intact structure and stay there until officials direct you to a clean evacuation route ³. For planning, it recommends an initial hazard boundary of 250 metres around the site, and a shelter zone of 500 metres in all directions and 2,000 metres downwind ³. These are initial planning distances for responders, not boundaries for the public to measure; follow the perimeter your local authorities announce.

The NRC's general rule applies throughout: minimize time near the material, maximize distance from it, and use shielding against external exposure and inhalation ².

How do you decontaminate yourself?

Once you are inside, taking off your outer layer of clothing can remove up to 90% of radioactive material ⁴⁵. Put the clothing in a plastic bag or sealable container and place it away from people and pets ⁵. Wash your hands, face and uncovered skin with soap and water, or use a moist wipe or damp cloth if there is no sink ⁵. If you can, take a warm shower and wash your hair with shampoo or soap, without scrubbing or scratching the skin ⁵. Ready.gov adds: do not use household cleaning wipes on skin, and hand sanitizer does not protect against radioactive material ⁴.

The full steps, including for pets, are in our decontamination guide.

Should you take potassium iodide?

Usually not. The CDC says potassium iodide (KI) protects only against radioactive iodine, does not protect against other types of radioactive material, and protects only the thyroid ⁶. The material in a dirty bomb may not be radioactive iodine at all: the source in Goiânia, for example, was caesium-137 ⁷. Take KI only if public health or emergency response officials, or a healthcare provider, tell you to ⁶. Our potassium iodide guide explains when it helps.

What official agencies recommend

• CDC (United States): get inside, stay inside, stay tuned; anyone injured by fragments or contaminated with dust needs medical care ¹.
• NRC (United States): limit time, increase distance, use shielding; authorities will advise either sheltering in place or leaving the immediate area once the material is identified ².
• Ready.gov / FEMA (United States): shelter in the most protective location for the first 24 hours; remove outer clothing and wash ⁴.
• Government of Canada: shelter for at least 24 hours with doors, windows and air systems closed. Canada differs on one point: it says to remove contaminated clothing and wash if instructed to do so, following officials' advice ⁸, while the CDC presents self-decontamination as a step to take once you are inside ⁵.
• HHS REMM (medical guidance): move to an intact building and stay there until officials direct you to an uncontaminated evacuation route ³.

Frequently asked questions

Can a dirty bomb cause a nuclear explosion?

No. The CDC states that a dirty bomb cannot create an atomic blast ¹. It is an ordinary explosion; the radioactive material only adds contamination ³.

How far does the contamination spread?

It depends on the size of the explosive, the amount and type of material, how it is dispersed and the weather ². The NRC says radiation could be dispersed within a few blocks or miles of the explosion ²; U.S. medical guidance gives a range from a single street or building up to several square miles ³.

Am I in danger if I was a few streets away?

The CDC says only people very close to the blast would receive enough radiation to become seriously ill right away ¹. Further away, the precaution is to avoid breathing dust and smoke by getting inside, then to remove outer clothing and wash ¹⁵.

How long should I stay indoors?

Ready.gov says sheltering usually lasts at least 24 hours, and Canada says to be prepared to shelter for at least 24 hours ⁴⁸. Leave only when officials say it is safe ⁴.

Will a dirty bomb make my home uninhabitable?

Not necessarily. The NRC warns that cleanup of an affected area may take considerable time and expense ². In Goiânia, 42 of 159 houses monitored needed decontamination ⁷. Officials decide which areas are restricted, based on measurements.

Make it part of your plan

A dirty bomb calls for the same first moves as other radiation emergencies: know where the nearest sturdy building is, where to undress and wash, and how you will receive official alerts. The Phaenyx personal plan brings the official guidance for your country together in one written household plan. Build your Phaenyx plan.

Sources

1. U.S. Centers for Disease Control and Prevention (CDC) — Radiological Dispersal Device (RDD) — https://www.cdc.gov/radiation-emergencies/infographic/radiological-dispersal-device.html (accessed 2026-10-20)
2. U.S. Nuclear Regulatory Commission (NRC) — Backgrounder on Dirty Bombs (February 2022) — https://www.nrc.gov/reading-rm/doc-collections/fact-sheets/fs-dirty-bombs.html (accessed 2026-10-20)
3. Radiation Emergency Medical Management (REMM), U.S. Department of Health and Human Services — Radiological Dispersal Devices (RDDs) — https://remm.hhs.gov/rdd.htm (accessed 2026-10-20)
4. Ready.gov (FEMA) — Radiation Emergencies — https://www.ready.gov/radiation (accessed 2026-10-20)
5. U.S. Centers for Disease Control and Prevention (CDC) — How to Self-Decontaminate after a Radiation Emergency — https://www.cdc.gov/radiation-emergencies/prevention/self-decontaminate.html (accessed 2026-10-20)
6. U.S. Centers for Disease Control and Prevention (CDC) — Potassium Iodide (KI) — https://www.cdc.gov/radiation-emergencies/treatment/potassium-iodide.html (accessed 2026-10-20)
7. International Atomic Energy Agency (IAEA) — Radiation sources: Lessons from Goiânia, IAEA Bulletin 4/1988 — https://www.iaea.org/sites/default/files/publications/magazines/bulletin/bull30-4/30402781017.pdf (accessed 2026-10-20)
8. Government of Canada — Radiological and nuclear emergencies – Get prepared — https://www.canada.ca/en/services/policing/emergencies/preparedness/get-prepared/hazards-emergencies/radiological/how-prepare.html (accessed 2026-10-20)