Dr Jack Denny, Lecturer at the University of Southampton, talks to AOAV about his and his partners’ research into blast wave propagation in urban environments, and how engineering and data-driven approaches can both inform response strategies and complement ongoing advocacy campaigns to reduce harm from blast injuries.
Just to start, can you introduce yourself, and give a brief overview of your personal research interests and the broader IBRN mission?
I’m Dr Jack Denny, Lecturer in Structural Engineering in the Civil Engineering Department at the University of Southampton, and I investigate the devastating effects of explosions using experimentation and computational modelling. I want to improve our understanding of blast wave propagation in urban environments, specifically, how shock wave interaction with structures modifies loading effects (i.e. the effects caused by loads applied to a structure from a blast wave that comes immediately after an explosion) and the consequences this has for blast injury risk and protective design.
The vision of the International Blast Injury Research Network (IBRN) is to drive innovative research to reduce harm from blast injuries. We launched the IBRN in 2019 because we identified that leading blast research was often focused on military, not civilian, situations and perspectives. As an example, our research has shown that in the last two decades, more than 80% of funding for blast injury-related research came from the US Department of Defense [2]. Addressing this gap, we brought together individuals from multiple disciplines and established the IBRN to improve research within the civilian context and at a holistic level. The IBRN has catalysed dialogue between different disciplines ranging from blast engineering, public health, medicine, modelling, simulation and many more. This has fostered collaboration among academia, clinicians, humanitarian organisations, research charities such as AOAV, and others – facilitating ongoing multidisciplinary research into the humanitarian consequences of blast injury. The IBRN has hosted two workshops in Cape Town and we plan to hold a third one in 2023. We have developed an ambitious and far-reaching research agenda and begun to deliver on our goals, some of which you can read about in peer-reviewed joint publications [1-4] and our online reports [5,6].
Can you discuss the causes and patterns of harm when explosive weapons are used in urban rather than rural or less built-up environments? What specific injuries from explosions become more likely in urban areas when blast waves reflect off walls and buildings?
Following an explosion, blast injuries are caused by multiple injury mechanisms, and urban settings present additional hazards in comparison to less built-up areas. The presence of buildings, structures, vehicles and other objects present fragmentation hazards (e.g. high velocity projectiles of debris, glass fragments etc.), which are responsible for so-called ‘secondary’ blast injuries. Penetrating wounds and lacerations caused by glass fragments from windows subjected to high explosive pressures (glazing or window failure) are common injuries from urban explosions, presenting a significant challenge for protection engineers and architects. Buildings also present a hazard from ‘tertiary’ or crush-type blast injuries caused by complete or partial structural collapse, or from being thrown against objects or surfaces due to the powerful blast winds.
‘Primary’ blast injuries are caused by exposure to high pressures from the blast wave itself. Depending on the magnitude (and duration) of these blast pressures, a range of primary blast injuries can be caused, with common examples including ear drum rupture, pulmonary (lung) injury and traumatic brain injury. In built-up environments, the blast pressures responsible for these injuries can be significantly modified due to reflections, shielding and channelling effects caused by the blast wave interacting with different structural obstacles and buildings.
Collaborative research between the University of Southampton (Dr Jack Denny), University of Sheffield (Prof Genevieve Langdon, Dr Sam Rigby, Prof Andy Tyas) and University of Cape Town (Prof Steeve Chung Kim Yuen, Dr Sherlyn Gabriel) aims to improve understanding of explosions in urban settings to better protect people and infrastructure. Our early studies have shown that certain primary blast injuries become more likely in urban areas when blast waves reflect off walls and buildings. Our work has shown that channelling effects, where a blast wave is reflected and ‘squeezed’ between two buildings, can amplify and extend the loading effect at certain locations. In these situations, the likelihood and severity of primary blast injuries such as ear drum rupture and blast lung injury can be significantly increased. So far, we have modelled relatively simple geometries and explored methods to ‘scale-down’ models (an incomplete representation of a more complicated system) representing simple urban environments for blast testing. As the work progresses, we aim to increase the complexity of models with accompanying experiments until it is possible to produce a high-fidelity, validated cityscape model.
How do blast and blast injury research complement ongoing civilian casualty tracking work, advocacy campaigns, and policy impact with regards to EWIPA?
The use of explosive weapons in populated areas (EWIPA) is becoming more common due to the shifting nature of conflict into urban areas, as seen in Ukraine, and terrorist attacks using improvised explosive devices (IEDs). As your research at AOAV shows, when explosive weapons were used in populated areas, civilians made up more than 90% of those killed or injured.
EWIPA is a priority issue for the United Nations (UN), where the Irish Government has recently championed a Political Declaration to protect civilians from EWIPA. The International Committee of the Red Cross (ICRC) designated EWIPA as a key priority and is advocating avoidance policies. The UN Institute for Disarmament Research (UNIDIR) has produced a framework for analysing immediate and long-term impacts, aligned with the UN Sustainable Development Goals.
While such advocacy is critical, the UN has also acknowledged that action needs to be supported by scientific research, to understand and evidence the consequences of EWIPA on health and wellbeing. In the absence of high-quality data, this is where we believe that a blast engineering perspective can offer useful insight and evidence to support and prioritise these efforts in reducing harm.
Further research (into blast effects and blast injury modelling) would help to investigate and quantify why the use of EWIPA is particularly harmful, including specific scenarios, through exploring the underlying physics of blast interaction in urban environments. Engineering-driven approaches could be used to examine blast injury risk maps for different scale weapons systems in different urban scenarios. This would generate new quantifiable evidence of the risk and potential harm caused by different examples of EWIPA, which would complement ongoing advocacy campaigns, facilitate evidence-led decision-making and policy work to reduce harm.
How does blast research help inform prevention and response strategies when it comes to EWIPA?
In order to better protect people and infrastructure from the devastating effects of EWIPA, we must develop comprehensive understanding of, and the ability to predict, blast loading in urban environments. Through new and continued blast engineering research, we believe that new knowledge and modelling capability will help to inform both prevention and response strategies to EWIPA.
Improved knowledge of blast effects in built up areas could help to inform urban planning, risk assessments and strategies to prevent or mitigate harm from future explosive events. This could involve further research into blast protection, leading to novel materials and structural protection systems for more resilient infrastructure and increased protection for their occupants.
Combining advances in urban blast modelling with injury risk predictions, we can expect new and more accurate capabilities to model the consequences from increasingly complex and varied blast scenarios. Working with health stakeholders, these models could help to inform and assist with health system response and preparedness to potential attacks. For example, models could predict expected injury patterns and realistic casualty estimates, which would help health systems develop disaster management plans. Optimised response strategies will help to enhance health system resilience and better health outcomes for affected populations.
IBRN has identified loading “zones of relevance” equivalent to real-world events such as truck bombs, landmine detonations and backpack IEDs. Can you tell me more about that process, and the implications of the findings?
Pre-clinical blast injury studies often involve generating loading conditions in the laboratory to investigate blast injury mechanisms or testing therapeutics. We found that some injury studies demonstrated limited rationale for the explosive testing conditions they applied, with conditions primarily influenced by facility and equipment capabilities.
Last year we published two studies which took an engineering analytical approach to review loading conditions used primary blast injury studies and developed guidelines to improve the real-world relevance of the loading conditions adopted. In this work, we identified “zones of relevant” loading conditions (which effectively map combinations of blast pressures and durations) that are equivalent to real-world events such as truck bombs, landmine detonations and backpack IEDs. While the proposed guidelines are not definitive, the analysis presents ‘zones of interest’ to guide and inform the generation of blast loading conditions that are clinically relevant (to the primary blast injury type of concern), realistic (corresponding to real-world threats) and practical from a testing perspective. We hope that this work will help the community to generate valid, clinically-relevant loading conditions to ensure more meaningful outcomes, which in the long term could translate into improved therapeutics and better health outcomes.
These ‘zones’ were derived on the assumption of idealised explosion scenarios. Through further work, we hope to be able to extend the applicability to different complex environments. While the primary motivation of this work was to establish guidelines for pre-clinical blast injury studies, the methodology could support modelling injury risk for real-world blast threats. For example, for a known blast threat, blast injury risk can be calculated at different distances away from the detonation, which if overlaid with population data, could be used to derive potential casualty estimates. Such information could be useful for informing and prioritising disaster management, health system preparedness and response.
According to data collected by AOAV, improvised explosive devices (IEDs) caused 51% of civilian casualties between 2011 and 2021, and 91% of civilian casualties of IEDs in that time occurred in populated areas. How can blast injury research improve efforts to protect civilians outside of periods of open armed conflicts between states?
Improvised explosive devices (IEDs) are challenging to characterise from a blast engineering perspective due to the high number of variables concerning the design, explosive material(s), construction and method of deployment, which often involve added fragments to increase their lethality.
The Universities of Cape Town and Sheffield have worked together to develop an academic version of an “idealised IED” for small scale testing [7-8]. Prof Genevieve Langdon proposed using a cylinder of PE4 plastic explosive and a half-embedded ball bearing. The ball bearing is a simple representation of objects embedded in IEDs, and understanding what happens to those embedded objects is important for predicting the injuries that IEDs cause. Through novel experiments combined with computational modelling, they were able to gain insight into the flight and damage of the ball bearing. They were able to predict the effects of changing the object mass, the influence of blast wave reflections on its path, and that under certain conditions the embedded objects may break apart making their velocity and mass distribution much harder to predict. Their experimental work was used by BlastFoam, a computer code for simulating blast events, to validate their models.
Blast effects from an IED can be investigated by approximation to an equivalent mass of TNT. As an example, in the ‘zones of relevance’ work described previously, different ‘zones’ of loading parameters were calculated for different IED threats based on TNT equivalences reported in available literature. Understanding how explosions from IEDs interact with the built environment is key for determining loading distributions and corresponding injury risk in different urban scenarios.
Increased understanding and abilities to model IEDs can help to inform protection strategies, including infrastructure protection, protective design requirements, and safety distances upon detection of an imminent threat. Working with other disciplines and stakeholders, additional modelling can be undertaken to determine casualty estimates and health system response, supporting hazard management planning for health systems.
Can you tell me a little more about the use of social media to estimate the size of an explosion in near real-time, and how this can assist emergency responders and disaster management agencies?
After the devastating explosion in Beirut in 2020, IBRN colleagues at the University of Sheffield (including Dr Sam Rigby, Prof Andy Tyas and Prof Genevieve Langdon) developed a novel way of using social media footage to rapidly estimate the size of the explosion.
In many of these videos, the moment of detonation was clearly discernible, as was the arrival of the blast wave at the filming location (typically showing up as a large increase in the audio signal). Google Street view was used to establish exactly where each video was filmed, which enabled the radius of the blast wave to be tracked as a function of time. This radius-time relationship was compared against existing semi-empirical approaches to find a “best fit” explosive yield, which was found to be 0.5 kt TNT. In context, this is around 1/30th the energy of the atomic bomb dropped on Hiroshima at the end of WW2. Crucially, this study came up with a first-estimate of the yield of the explosion within less than 24 hours of the event, and such use of “citizen sensors” has great potential to be automated in the future.
Information about loads can be related to injury likelihoods in near real-time using automated tools, making emergency responders and disaster management agencies able to anticipate damage and casualty locations. Emergency responders can be directed to regions of the city with high concentrations of casualties more efficiently, and hospitals could be better prepared for the types of injuries that people are likely to arrive with.
What are some of the limitations of blast and blast injury research at the moment? How can we best move forwards in impactful and meaningful ways?
In the blast injury and explosive violence research domain, data and data collection are frequently raised as a critical limitation. Understandably, mass casualty events strain health systems and national responses often abandon data collection. This is regularly raised as a critical issue: data disaggregated by gender, disability, age, and weapon type is often missing. This prevents deeper analysis of how different contextual and environmental factors (e.g., weapon systems, urban settings, and population dynamics) contribute to the numbers and severity of casualties or the demographics affected. Today, there is still limited understanding of the patterns of harm caused by EWIPA in different scenarios (e.g. distinguishing the health impacts caused by a rocket attack in residential areas vs. terrorist attack in a market), making it difficult to anticipate the direct and long-term pressure placed on health systems.
From a research perspective, there is limited understanding of the loading conditions that occur in urban blast scenarios or ability to predict these complex physical processes. This is exacerbated by a huge number of variables such as different explosive threat types and urban configurations. Furthermore, while injury epidemiology is relatively well described from the standpoint of military personnel, it is vastly less so for civilians, who sustain injuries unprotected by body armour. Collectively, this limits our understanding of the link between a victim’s actual blast exposure and injury outcome, and therefore our ability to prepare for future threats.
Moving forward, improved data and data collection methodologies are clearly needed. Enhanced data would help to better evidence the problems caused by EWIPA, helping to prioritise humanitarian responses and inform policy to reduce harm. Higher quality data will also benefit research by improving the accuracy of modelling efforts, inform blast protection strategies and injury sciences to increase preparedness and response. Ultimately, these efforts will require multidisciplinary working and close collaboration between different stakeholders.
Who should be paying more attention to blast injury research?
In an ideal world, the occurrence and threat of blast injury could be eliminated. In the meantime, however, there is an urgent need for further research to advance understanding to improve treatments, increase preparedness, protection and response to attacks and inform policy to reduce harm.
As a complex, global challenge, solutions inevitably require a collaborative and multidisciplinary effort from multiple stakeholders. As such, it should be the collective responsibility for defence, humanitarian organisations, advocacy groups, charities, scientists and funders to work collaboratively to share best practice, prioritise and drive (blast-related) research that can reduce suffering.
Is there anything else you’d like to share on the topic of blast injury research, civilian casualty tracking, or advocacy?
We are pleased to announce that our third IBRN event will be taking place in Beirut, Lebanon in March 2023. We are organising a hybrid workshop (in-person and online), which will focus on building understanding of the consequences and response to the devastating 2020 Beirut explosion. The event will also cover the broader research challenges of explosions in urban settings including blast injury, civilian casualty tracking and data collection. If you are interested in participating in this event, please see our website page to keep up to date and for registration.
1: Denny JW, Dickinson AS, Langdon GS. Defining blast loading “zones of relevance” for primary blast injury research: A consensus of injury criteria for idealised explosive scenarios. (2021). Med Eng Phys [Internet]. 93:83–92. Available from: http://dx.doi.org/10.1016/j.medengphy.2021.05.014
2: Denny JW, Dickinson AS, Langdon GS. (2021). Guidelines to inform the generation of clinically relevant and realistic blast loading conditions for primary blast injury research. BMJ Mil Health [Internet]. Available from: http://dx.doi.org/10.1136/bmjmilitary-2021-001796
3: Denny JW, Brown RJ, Head MG, Batchelor J, Dickinson AS. (2020). Allocation of funding into blast injury-related research and blast traumatic brain injury between 2000 and 2019: analysis of global investments from public and philanthropic funders. BMJ Mil Health [Internet]. Available from: http://dx.doi.org/10.1136/bmjmilitary-2020-001655
4: Denny J, Langdon G, Rigby S, Dickinson A, Batchelor J. (2022) A numerical investigation of blast-structure interaction effects on primary blast injury risk and the suitability of existing injury prediction methods. International Journal of Protective Structures. Available from: https://doi.org/10.1177/20414196221136157
5: Denny J, Brown R, Batchelor J, Langdon G. (2019). Examining the state of research: Defining the challenges and opportunities for blast injury research: Workshop Report. March 2019, Cape Town, South Africa [Internet]. United Kingdom: University of Southampton; Available from: https://www.southampton.ac.uk/news/2019/03/blast-injury-network.page
6: Denny J, Dickinson A, Brown R, Batchelor J, Jenssen G. (2019). Sizing up blast injury research – transforming the effectiveness and relevance of blast injury research [Internet]. United Kingdom: University of Southampton; Available from: http://dx.doi.org/10.6084/m9.figshare.7624148.v1
7: Qi R, Langdon GS, Cloete T & Yuen SCK (2020) Behaviour of a blast-driven ball bearing embedded in rear detonated cylindrical explosive. International Journal of Impact Engineering, 146. https://www.sciencedirect.com/science/article/pii/S0734743X20307685
8: Langdon GS, Qi R, Cloete TJ & Chung Kim Yuen S (2022) Influence of ball bearing size on the flight and damage characteristics of blast-driven ball bearings. Applied Sciences, 12(3).
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