By Dr. Carlos Rojas Palma, Nuclear Emergency Preparedness R&D, Belgian Nuclear Research Center (SCK CEN), Belgium
Perhaps one of the most publicized terrorist attack scenarios involving the dispersion of radioactive material by means of conventional explosives is the so-called dirty bomb or, in fancy terms: a radiological dispersal device (RDD). In this context, the idea is to make use of a conventional radioactive source, which may consist of a fine powder such as those used in blood-irradiation facilities or for industrial applications in gammagraphy applications to study the welding conditions in pipelines. In the former case, the dispersion of radioactive material is possible, whereas in the latter case, there is a need to produce fine particles from a solid piece of metal, which is by no means easy.
A number of scientific works have studied the physical properties of both powder and solid materials after being exposed to the high temperature and pressure resulting from an explosion, and this, as a function of the device design (geometry) and type and charge of explosive used. The details of these studies have been classified. Other studies have focused on the fate of the dispersed material after the explosion, which is a function of the weather conditions and location. Once again, outdoor consequence assessments associated with the dispersion of radioactive materials are a sensitive issue, and therefore the information is not readily available; however, the results can be useful to those with security clearance, such as policymakers and emergency planners.
Under the 7th Framework Program – Security, the CBRN crisis management, Architectures, Technologies, and Operational procedures (CATO) proposal was submitted to the European Commission. Among the many objectives set out for the project, the consortium had to develop a CBRN consequence assessment and decision support system and derive guidelines for first responders based on a set of field experiments involving the dispersion of materials.
The establishment of a clean-dirty line is essential as to ensure contaminated equipment does not leave the area prior to being decontaminated.
After a long legal and ethical scrutiny, the European Commission awarded the proposal with a grant; however, the work package associated with the design, development, deployment and consequence assessment of field experiments had to be classified, and the appropriate rules to dealing with classified information had to be put in place. The discussion below is based on the unclassified results, which have been published in 20201.
Conducting studies on an Improvised Explosive Device (IED) and Vehicle-Borne Improvised Explosive Device (VBIED) with a radioactive payload is no easy task in Europe. Indeed, the amount of radioactive material allowed is pretty low, which means that most of the radioactivity will be deposited at-or near ground zero.
To avoid this problem, the team designing the experiments opted for the use of Cesium Chloride (CsCl) stable, which has the same physicochemical properties of the CsCl used in blood-irradiators but is not radioactive. Some of the experiments used FeO (Iron oxide) instead to better visualize the spreading of the plume or the contaminated area, in particular during VBIED tests.
Figure 1 shows the experimental setup, which consisted of dummies wearing regular clothes, with cellulose filters placed on the chest and shoulder to collect fallout and a set of high-volume air and particle segregated samplers. The former collects airborne particles while the latter separates particles according to their aerodynamic diameter, i.e., size in µm (0.000001 meter). Deposition samples were collected on plates covered with adhesive tape, which would then be removed and sent to the laboratory for analysis. All samples were collected by the counter-terrorism unit of the UK Police. This way, all environmental samples were treated as forensic evidence. Dummies and detection equipment were surrounded by two walls, which would resemble a street canyon, adding turbulence to the dispersion conditions. Each experiment was captured using hig- speed cameras and a drone also equipped with a high-resolution camera.
Figure 2 shows a typical deposition collection plate showing the evidence labeling.
The field experiments were carried out in an area equivalent to a football pitch, surrounded by trees and which could be similar in terms of dispersion conditions to a park in an urban area. The explosives used were built using Internet know-how. Again, details on the exact venue as well as sample collection and analysis can be found in1.
DOs and DON’Ts
Although I cannot elaborate on the specifics of the IEDs and VBIEDs consequence assessment as the information is classified, we one could safely assume that the affected area will have a diameter of about 50 m around ground zero. This, of course, will depend on the atmospheric conditions. However, this generic perimeter could be useful when developing response plans as to where to set the various perimeters outlining the red, orange and green zones. Police officers regulating access to these zones are to wear face respirators and gloves.
Even 15 min after detonation, non-negligible air concentrations were found, and this implies that the victim triage and their subsequent extraction would have to be carried out by firefighters wearing full personal protective equipment including self-contained breathing apparatus. The establishment of a clean-dirty line is essential as to ensure contaminated equipment does not leave the area prior to being decontaminated.
The observed particle size distribution is bimodal, which means that high concentrations were found in the large particle size around 10 µm aerodynamic diameter equivalent region. This is a well-documented phenomenon attributed to the effect of the fireball and high temperatures associated with the explosion. Given their high deposition velocity, these particles are likely to deposit near ground zero. On the other hand, a high concentration of particles was found in the micrometer size range and this size fraction, which is inhalable, therefore, the use of face respirators is mandatory as well as proper procedures to avoid cross-contamination when removing the face respirators and gloves are to be properly taught and trained. Appropriate waste management protocols are also to be put in place.
Since 9/11, countries around the world have introduced radiation detection equipment as a standard-issue among first responders. However, these devices may induce a false sense of protection as they will only indicate the presence of radiation and/or levels of radiation exceeding a predetermined safety threshold. The first responders who need to enter the red zone should carry a radiation detector and communicate the radiation levels to a properly trained radiological expert/hazmat specialist via the radio. The expert will then determine the duration of the operation, depending on the radiation levels reported. The best protection they will have will be provided by minimizing the time in the red zone, maximizing the distance between the hotspot and them, and using any piece of material to create an improvised radiation shield while performing their life-saving activities. Medics must wear protective gear and treat trauma injuries first regardless of the presence of radioactive contamination. Detailed guidelines on the management of mass casualties after a malevolent use of ionizing radiation can be found in Carlos Rojas-Palma et al. (2009) www.tmthandbook.org
In terms of impact, a VBIED yields 1000-fold less concentrations as compared to an IED as most of the material will remain inside the vehicle. This can pose serious difficulties to forensic experts as the retrieval of evidence will be hard or even impossible due to the high-levels of radiation. The assistance of specialized personnel in handling high level radioactive waste will be necessary.
I am grateful to the European Commission for supporting this project through grant 261693 to all my colleagues who participated in these experiments and who are listed in the above-mentioned reference, as well as to the UK Police Counter Terrorism Unit for their invaluable support during the field operations.
1Carlos ROJAS-PALMA et al. J. Radiol. Prot. 40 (2020) 1205–1216 (12pp)
About the Author
Carlos Rojas-Palma obtained his Ph.D. (Magna Cum Laude) in Physics from the University of Antwerp, Belgium. Since 1994 works at the Belgian Nuclear Research Centre (SCK CEN), and spent more than a decade working on nuclear safety and radiation protection program under Euratom. He has coordinated a number of research projects for the European Commission’s Euratom 5th, 6th and 7th framework programmes. From 2004 to 2007 Carlos lead an expert group tasked to improving the International Action Plan of the International Atomic energy Agency for Strengthening International Assistance in case of a radiological or nuclear incident. In the past 6th Framework Program, Carlos coordinated the specific targeted research project TMT Handbook: Triage, Monitoring and Treatment of the public exposed to the malevolent use of ionizing radiation. He is currently engaged in European CBRN preparedness and resilience activities as well as countering RN terrorism. He is currently security expert to the Research Executive Agency of the EC as well as to DG HOME and lectures at the CBRN Master’s program of the University of Rome, Tor Vergata.
