ANR URB(EX)3 Project:
URBAN EXPLOSIONS: EXPERTISE AND EXPERIMENTS
Experiments and quick modeling for explosions in urban environments.
Beyrouth, one year later
The international community is currently commemorating the first anniversary of the tragic accident that left Beirut in mourning. This disaster (one of the largest non-nuclear explosions in history) left an impressive toll: 218 dead, almost 6,500 injured and an estimated 4 billion euros worth of damage [1].
Authors: Naeblys and inception-D
This accident demonstrates that explosions in urban or peri-urban environments are still a major risk for people and infrastructure, whatever the origin of the explosion: a gas leak (Trévise street explosion in Paris on January 12, 2019), an industrial accident (AZF on September 21, 2001, Beirut, etc.) or a terrorist attack (Oslo on July 22, 2011).
Evaluate risks
There are three kinds of explosion effects:
- an airborne blast wave that generates overpressure, leading to structural and human impact (“primary” injuries due to direct effects, and “tertiary” injuries due to the impact of the body thrown by the blast wave),
- projectile damage caused by fragments (from the immediate surroundings of the explosion or propelled by the blast wave), resulting in “secondary” blast-related injuries,
- thermal effects caused by the “fireball”, the effects on human beings being part of “quaternary” injuries.
Direct fragments are quickly stopped by buildings in urban areas and thermal effects are generally very localized. On the other hand, suppressive effects can cause damage over long distances: 80% of injuries are caused by broken glass, which is vulnerable to very low overpressure and can therefore shatter at a great distance from the explosion site.
Assessing the risks associated with explosions presents a key challenge: quickly identifying danger zones requires calculating isodamage circles “on bare, flat ground”, which do not factor in the influence of the urban environment:
- urban canyons (streets surrounded by buildings) channel the effects of the airborne shockwave, leading to danger zones that are significantly larger than those predicted for open conditions,
- the wave is reflected multiple times by the walls of buildings, which also increases danger zones,
- the wave passes around buildings from the sides or from above, inducing diffractions that reduce its damaging effects.
In any case, using a simplified isodamage circle approach (also used to determine overpressure effect zones for Technological Risk Prevention Plans) in an urban environment is not the safest solution…
The most commonly used solution to precisely assess the effect of explosions in complex environments is 3D numerical calculation codes. However, these tools have several drawbacks, which make them only suitable to study the near field of an explosion:
- they require substantial resources (supercomputers) and specific technical skills,
- calculations can take days or weeks, even if they are performed on clusters of several hundred processors,
- the intrinsic limitations of numerical codes make it impossible to calculate precise long-distance overpressures and danger zones.
Another, more complex (and more risky!) route is to develop fast but reasonably accurate analytical models that can handle urban fabric characteristics (derived, for example, from IGN or OpenStreetMap data)… This approach was used by the author, then at CEA/DAM/Gramat, in collaboration with Richard Soulié (currently at CETID [2]) when developing the FLASH code [3] (cf. FLASH: Fast Lethality Assessment for Structures and Humans, 24th MABS conference, 2016), as part of the ANR [4] DEMOCRITE project. This code contains several flaws, the most significant being the calculation of a single wave, ruling out any ability to render a complex pressure signal combining different reflected and diffracted waves…
The ANR URB(EX)3 Project
The URB(EX)3 project is a simplified version of the much more comprehensive SIRENE project [5], which has not yet secured funding.
URB(EX)3 focuses on studying explosions in urban areas, and includes:
- an experimental component at INSA Centre-Val de Loire, Bourges site (PRISME laboratory), under the supervision of Isabelle Sochet. Isabelle’s team is recognized internationally for the quality of its small-scale experiments using hemispherical or spherical propane/oxygen charges.
- a modeling component led by APEX solutions (which also coordinates the project as a whole), using a totally different approach to FLASH, and, to our knowledge, one that has never been used before in the literature. This innovative approach was partially validated by preliminary work done with our own funds.
The project has an ambitious goal: the URB(EX)3 model will calculate the consequences of an explosion in an urban area in about one minute (for a study area with a radius of 300 m), using a standard PC, and dealing with both the direct wave and any number of reflected and diffracted waves. The model will be integrated into a version of the DEMOCRITE platform by IT Link, which has already produced the first version. The experiments at Bourges will quantify the uncertainties of the model, both for single phenomena (diffraction, regular reflection, Mach reflection) and on the scale of an entire district. The results will also be compared with 3D numerical simulations during the project (VIPER ::Blast code and DALPHADT code).
The final software will be used for pre-crisis (training, scenario evaluation, etc.), crisis (rapid calculation of danger zones to help evacuate people) and post-crisis purposes (assessment of the quantity of explosive responsible for the damage observed after an explosion).
The project was submitted as part of the ANR’s 2021 generic call, and was selected after two evaluation phases. It will receive co-funding of 316 k€. It will run for 24 months. We will start work at the beginning of January 2022, and will use the end of 2021 to draft the consortium agreement, draw up the detailed program of experiments to run, recruit as planned and build a community around the project.
The ecosystem of an “explosion in a complex environment”
The URB(EX)3 project has been accredited by the SafeCluster competitiveness cluster. It also received letters of support from leading organizations in the field, who will participate in the project’s monitoring committee and have access to the detailed research results and the tools developed:
- IRCGN (National Gendarmerie Criminal Research Institute),
- LCPP (Central Laboratory of the Paris Police Prefecture),
- EURENCO (European leader in energetic materials ),
- IRSN (Institute for Radioprotection and Nuclear Safety),
- CETID (Center for Expertise in Defense Infrastructure Techniques),
- INERIS (National Institute for Industrial Environment and Risks),
- CEA, Gramat center (Atomic Energy and Alternative Energies Commission).
We are also working with EOD-NEDEX groups [6] and the Swiss laboratory Spiez, well known for its work on explosions in tunnel networks.
Isabelle Sochet is also coordinating the international SATURN project funded by “Le Studium” (The Institute for Advanced Studies of the Loire Valley ), which APEX solutions is also involved in. SATURN aims to gather detailed experimental data at different scales on explosions in urban environments to validate numerical codes and simplified tools. The other participants are leading researchers in this field: Samuel Rigby (UK), Oren Sadot (Israel), Alex Remnikov (Australia) and Ernst Rottenkolber (Germany). SATURN will thus be the perfect complement to URB(EX)3, and we have high hopes for the synergies between both projects.
This doesn’t mean we’re abandoning the other projects scheduled for SIRENE. The topic of explosions in tunnel networks is being explored by Valentin Guernion, from IMT Alès, during his internship at APEX solutions, in collaboration with the Spiez laboratory. The other companies involved in SIRENE: IT Link is working on various technologies, including the Unity video game engine and Google Glass Enterprise Edition 2; RS2N is continuing its work on the numerical calculation of explosions (detonation and post-combustion) and Wisebim has extended its range of tools to convert 2D plans into BIM format… We’re keeping up the good work!
These projects, which focus on explosions in complex environments, will allow us to build up a dynamic community with a wealth of experience and an openness to external exchanges.
See you in January 2022!
We’ll be putting the project summary, task details and projected Gantt chart online in January, along with a bibliography on explosions in urban environments.
We’ll be posting regular updates and detailed articles about URB(EX)3 on the APEX solutions website, as well as scientific papers and presentations at major conferences in the field: MABS, ISIEMS, SUSI [7]…
Like the ANR, we are committed to an “Open Science” approach, the only limit being the protection of intellectual property rights: “as open as possible, as closed as necessary”. Most of our results will therefore be available to the international community on the HAL platform.
Please feel free to share your datasets, articles and results the same way, and see you soon for the next part of the adventure!
References
[1] Source: https://fr.wikipedia.org/
[2] Center for Expertise in Defense Infrastructure Techniques
[3] Flash Lethality Assessment for Structures and Humans
[4] National Research Agency
[5] SIRENE covered explosions in urban environments, in buildings and in tunnel networks (as well as any coupling between these environments), and dealt with blast effects, projections, thermal effects (including BLEVE-type industrial accidents) and quasi-static pressure propagation. The recovery of geometric data (cities and buildings) using innovative methodologies was also included in the project, as well as full validation using reduced-scale experiments and 3D numerical simulation.
[6] Explosive Ordnance ; Neutralization, Removal and Destruction of Explosives.
[7] Military Aspects of Blast and Shock, International Symposium for the Interaction of Munitions with Structures, Structures Under Shock and Impact.
