A dirty bomb is a device that combines radioactive materials with conventional explosives. Global terrorist organizations are believed to be interested in and capable of constructing dirty bombs and launching attacks with them. There are only two documented cases of terrorist use of dirty bombs in the world today. Both incidents occurred in Russia. In 1995 Chechen insurgents buried a cesium-137 dirty bomb in a park in Moscow and alerted the media before its detonation. In 1998 a container of radioactive materials was found attached to an explosive mine near a railroad line in Chechnya. Dirty bombs are attractive to terrorists because they are relatively easy to acquire and have the potential for causing casualties, contamination of widespread areas, adverse psychological effects, and economic disruption. A dirty bomb threat potentially poses a medical and public health disaster.
A dirty bomb can be made from traditional dynamite, trinitrotoluene (TNT), ammonium nitrate, or a variety of other explosive materials. When detonated it kills or injures by the initial blast, which causes damage from the expansion of hot gases, and by dispersing radioactive materials that are highly toxic over a wide geographic area without a nuclear explosion. The dispersal effects of a dirty bomb depend on the amount of explosives used, the physical form of the radioactive source, and the atmospheric conditions. A dirty bomb is also known technically as a radiological dispersal device (RDD).
Many different radioactive sources can be used to fabricate a dirty bomb. Radioactive sources can be obtained illicitly from hospitals and medical clinics, industrial radiography and gauging devices, food sterilizers, power sources, communication devices, navigator beacons, oil well logging, and scientific research laboratories. Some common radioactive sources that have a high probability of being used as a dirty bomb based on their availability include cobalt-60, strontium-90, cesium-137, iridium-192, radium-226, plutonium-238, americium-241, and californium-252. Alpha-emitting radiation sources pose serious health hazards if they are inhaled, ingested, or deposited in an open wound. Beta-emitting sources can cause deep beta burns on the skin. Gamma rays may penetrate body tissues and cause deep tissue injury.
The most likely dirty bomb scenarios would involve the use of either a few small low-level radioactive sources or a large amount of highly radioactive sources combined with high explosives. The first scenario considers use of a dirty bomb containing a few curies of a gamma-ray source, such as cesium-137, combined with a few kilograms of high explosive. In this case the dirty bomb may be used with the primary intent of causing fear or panic among people and disrupting their community. Because the amount of radioactivity is small, the radiation exposure to individuals would be low and no immediate effects on health would be expected. The probability of long-term health effects would be small.
The second scenario considers use of a dirty bomb containing large sources of penetrating radiation coupled with sophisticated high explosives. The detonation would disperse considerable amounts of radioactive material over a large area. Persons injured by the blast are likely to be contaminated with radioactivity and may receive life-threatening doses of radiation. Such a device is intended to kill tens or hundreds of persons, injure and sicken hundreds or thousands, and cause widespread panic.
Recognizing that a conventional explosive device has been detonated may be simple because of the associated blast. However, it may take considerable time before the radioactive component of the dirty bomb attack is recognized. Therefore it is important that first responders use radiation-detection equipment to identify a radioactive component after any explosion.
Recognition of acute radiation injury is based on the patient’s medical history and clinical findings. The extent of radiation injury depends on three factors: depth of penetration of the radiation, dose of radiation absorbed, and volume of tissue irradiated. For localized radiation exposure the initial signs of injury might be a radiation burn, including erythema, blistering, or desquamation. With a low whole-body dose of 0 to 100 cGy from a dirty bomb, a patient would generally have no symptoms. With a moderate whole-body dose of 100 to 200 cGy, the patient may exhibit the prodromal phase (nausea and vomiting) of acute radiation syndrome. At doses exceeding 300 cGy, patients would experience nausea, vomiting, diarrhea, erythema, and fever. A useful method of predicting the clinical severity of radiation injury is the time to onset of vomiting. If the time to vomiting is less than 4 hours, the patient has received a high dose of radiation.
Laboratory data show that early changes in lymphocyte counts are associated with the severity of radiation injury. Absolute lymphocyte counts less than 1000 mm 3 and greater than 500 mm 3 indicate moderate and severe levels of radiation exposure, respectively. Complete blood counts can be repeated every 4 to 6 hours to evaluate lymphocyte depletion kinetics. The appearance of dicentric chromosomes in peripheral blood lymphocytes is also useful in the calculating exposure dose. In patients who have developed acute radiation syndrome, within 2 to 3 weeks bone marrow suppression may occur with associated neutropenia, lymphopenia, and thrombocytopenia.
Pre-Incident Actions
One of the most important preemptive actions that emergency medical service agencies, hospital-based emergency departments, and outpatient facilities should do is to determine whether their community is a possible target for a terrorist dirty bomb attack. Coordinating with local and state law enforcement and response agencies should provide a framework in which to assess the dirty bomb threat and develop a medical radiation incident or injury protocol. The protocol should be incorporated into the overall disaster plan. The radiation disaster plan should address decontamination, security, radiation monitoring, and decorporation of radioactive materials. The hospital radiation safety officer should be included in the medical radiation response team. Hospital staff should understand the hazards of radioactive contamination and be trained in radiation-monitoring techniques. Staff would need access to dosimeters, Geiger-Mueller counters, and personal protective equipment. Radiation-detection capabilities are critical to an effective medical response. Hospitals should have a realistic decontamination plan for patients, a lockdown plan to control access, and evacuation plans. A radiation risk communication program is required for the public. As has been shown by the Fukushima Nuclear Plant accident in 2011 the most important task for scientists is to make available to the public scientific knowledge of the level of radiation risk resulting in more understanding of their potential health risks.
Post-Incident Actions
Emergency medical first responders arriving on the scene of a dirty bomb incident should initiate actions to treat or evacuate casualties. All response personnel should be advised of the explosive and radiological hazards that may be present. Health care providers should advise others regarding safety measures to be taken to protect the public and to mitigate the radiation health effects. Patients evacuated from the scene and arriving at hospitals or medical clinics should be routinely monitored for radiation and decontaminated, as needed. Health care providers should control any exposure of hospital personnel to contamination. Moreover effective decontamination procedures are available to reduce the radiation contamination and to avoid an uncontrolled spread of the contamination. Clinicians should seek the assistance and cooperation of state and local authorities and inform them of casualties and possible hazards. Hospital radiation safety staff should periodically monitor the emergency department for radioactive contamination.
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