Gas! Gas! Gas! Attack of the hazardous cloud (and how to deal with it)
When a nasty material is released in to the air, whether accidentally or from a deliberate attack, there is potential for severe harm and disruption. How does the UK military deal with such scenarios? We explain how using novel scientific techniques minimises the impact and keeps troops and civilians safe.
Introduction
Anyone who has picked-up a newspaper or watched the news will be aware of the growing threats from non-state actors, like terrorist groups, which now sit alongside the more "traditional" threats from hostile states. In this new world, innovation and appropriate adaptation of current defence capabilities is needed. Specifically, many rogue nations and terror groups use asymmetric warfare and Chemical, Biological, Radiological or Nuclear (CBRN) weapons to achieve major impact. As a consequence, preparation and vigilance, rapid detection, and early response to a release of a hazardous agent could dramatically reduce the extent of human exposure, inform appropriate medical counter-measures and minimise the disruption. Furthermore, accurate reconnaissance and survey of the release location will both cut-down the necessary use of finite capability and the cost of the forensic investigation. How can we best prepare for such events? How can we make sure we’re alerted as soon as possible? How can we decide how to respond in the best possible way?
This article gives a succinct review of some of the steps within the UK MoD Warning and Reporting (WaR) process to deal with these challenges. These will be divided into three (potentially overlapping) phases for the purpose of this article: Pre-event, during-event and post-event. Although much of what is detailed here covers all CBRN doctrine, we shall specifically consider chemical releases.
Although we focus on the WaR process in a military context, equivalent ideas may also be appropriate for a homeland security setting, like the recent London Olympic Games, where the official terror threat was at “substantial”. For example, some pre-event preparations included the vaccination of hundreds of frontline health workers against smallpox in case of a biological terror attack by extremists turning to germ warfare, or, more widely publicised, the main Olympic Park in east London was protected by one of the biggest peace-time security operation ever seen, including the possible deployment of missile batteries to protect the capital from air attack.
Chemical weapons can be categorized by their physical characteristics, such as lethality, persistency and physical state (i.e. gas, liquid, or solid) when being delivered. This delivery can also be done in several different ways, as aerosols, mortars, artillery shells, missile warheads, mines, or aerial bombs.
There are several well known examples of chemical weapon use or occasions of severe threat. In a civilian context, liquid sarin, transported in plastic bags, was used in a terrorist attack on the Tokyo subway in March 1995, killing 8 and harming many more. Nerve agents such as sarin can paralyze and cause death in minutes just from a few droplets absorbed directly through the skin. By contrast, the military threat of a chemical attack during the Iraq war was well publicised but thankfully not realised. This hightened threat level followed the mass genocide of the Kurdish people in the closing days of the Iran-Iraq war in 1988. It’s believed multiple chemical were used, including mustard gas, sarin, tabin and VX.
Pre-Event
The pre-event phase is any time up to an affirmative detection. The old adage “failing to prepare is preparing to fail” is particularly pertinent in a CBRN WaR context. So this phase focuses on on-going monitoring and what’s called the Intelligent Preparation of the Battlespace (IPB), including detailed contingency planning (CONPLANs). Various ‘what if’ scenarios are considered using the process known as the 7 Questions1. These break down the procedure by which plans are made and actions taken. The questions help to summarise the activities and outcomes of the different stages. They are as follows:
1. What is the enemy doing and why?
2. What have I been told to do and why?
3. What effects do I want to have on the enemy and what direction must I give to develop my plan?
4. Where can I best accomplish each action/effect?
5. What resources do I need to accomplish each action/effect?
6. When and where do the actions take place in relation to each other?
7. What control measures do I need to impose?
Operational Analysis (OA)
This is a relatively slow time analysis, using operational research methods to determine the implications of potential chemical release scenarios and response strategies. Predictions are made of the hazard area and the physiological effects on the people inside it. OA can also help with medical planning and logistics.
Computer simulation models show how chemical agents spread using information about meteorology, terrain and agent properties. The models give a picture of how a cloud would disperse and move through urban and rural area. They can also be used for training as well as mission preparation- see box on dispersion modelling. Although OA is mainly employed pre-event, it can be used post-event to compare and analyse the planned scenario and the actual course of events. These lessons are valuable to future operations.
Sensor Placement
To respond effectively, we first need to reliably detect the agent’s presence as soon as possible. This may be achieved with sensor measurements. There are many types of available sensors, but whatever the specific characteristics, the decision must be made as to where to place them. Thus, an optimal sensor placement tool may be used to provide guidance. This will enable the best detection capability from the available kit, taking into account things like terrain, areas of high importance, sensitivity to false alarms and sensor networking.
Monitoring and Surveillance
On detection, the agent may be identified and in some cases quantified. In general, the sensors can be categorised into one of three types: generic point detectors- the cloud must pass over the sensor to alarm, stand-off area detectors- the sensor scans an area remotely, or specific detectors- these will only alarm for particular agents. Example detectors include the Lightweight Chemical Agent Detector (LCAD) (see Figure 1) and the Manportable Chemical Agent Detector (MCAD). However, important information about a release can also come from other sources like Intelligence, Surveillance, Target Acquisition and Reconnaissance (ISTAR) or the occurrence of casualties.
Figure 1: An instructor at the Defence CBRN Centre operates a Lightweight Chemical Agent Detector (LCAD).
During Event
This phase begins immediately after the detection of a chemical release. The emphasis needs to be on speed relative to accuracy. However, the decision maker should be aware of the uncertainty attached to the outcome of any action.
Source Term Estimation
To provide estimates of risk from a release, dispersion models, which predict downwind hazard areas, are used. This requires a source term describing the characteristics of the attack, such as the release location (where), time (when) and mass (how much). Unfortunately, especially during the initial phase of a release, we are usually in the dark about the true source characteristics and associated hazard areas. Thus, some form of source term estimation must be carried-out.
A number of different techniques have been developed for source term estimation. In particular, current NATO doctrine prescribes the use of, what’s known as, an ATP-45 template for rapidly producing a hazard area template from geometric rules. This means it can be generated using just pen and paper. A drawback is that this approach may significantly over-estimate the size of the hazard area and restrict the use of military capability. The subject of on-going research, more sophisticated methods are being developed which can potentially characterise the hazard more accurately and in real-time.
The necessary accuracy and timeliness of source term and hazard area estimates depend on the types of decisions to be made from them. For example, rapidly produced, over-estimates may be used to inform immediate evacuation and masking-up strategies and then more accurate estimates may be used to inform alternative route planning and the administering of medical countermeasures. The decision on which approach is most appropriate can roughly be matched to how close to a CBRN cell on the front-line, where there is likely to be less powerful computing available and greater urgency. Ultimately, the purpose of all these techniques is to improve the commander’s decision process- see box about source term estimation.
Figure 2: ATP-45 hazard template and an estimated plume from a dispersion model
Identifying the Special Source: A Brief Source Term Estimation Review
The field of source term estimation has been a focus of increased research interest in recent years. There are numerous innovative approaches proposed to address variants of this problem, including applications to volcanic emissions, oil spills and nuclear plant disasters. These methods include the use of a random search algorithm, simulated annealing and genetic algorithms. However, by-and-large, the emphasis of the research has been on two contrasting approaches: direct-inversion procedures and Bayesian inference.
In direct-inversion procedures an inverse solution is obtained using an adjoint advection-diffusion equation2. A specific application considers the reconstruction of the Chernobyl accident source term3.
Many of the Bayesian developments have focused on the use of Markov Chain Monte Carlo (MCMC) algorithms and a Reversible jump-MCMC algorithm for multiple source reconstruction. On-line Bayesian methods, such as Sequential Monte Carlo (SMC) allow the updating of belief given new information in near real-time4.
First Response
Any response, both in the short and longer term, must be considered in the context of the overall aims since every action will have numerous direct and indirect consequences. The initial action is to cordon-off the potential hazard area and make a decision about masking and other physical protection strategies, like the use of suits and gloves. Especially in the chemical release scenarios, first response will also include the immediate decontamination of personnel.
Figure 3: Troops practice masking-up drills during a CBRN drill.
Post Event
This phase begins after the initial response when more considered actions are possible.
Updated decisions must be made about what level of physical protection to adopt. This must consider the balance between CBRN protection and physiological and logistic burden. Wearing heavy, cumbersome protective gear can seriously affect the ability to effectively do even simple tasks. Command decisions must also be made about the decontamination of platforms, terrain, critical infrastructure and sensitive equipment including tanks and aircraft.
Forensic investigation of the release location would also be carried-out. This helps to obtain more detailed information about the release type and delivery method, which is useful for future incidents. In the British armed forces, the detection and decontamination within CBRN release scenarios is carried-out by the specialist unit, the Joint CBRN Regiment (see Figure 4 below).
Figure 4: Soldiers from the Joint NBC unit perform decontamination procedures during a logistical exercise
Clouded Thinking: A Brief Dispersion Modelling Review
When an agent is released into the atmosphere, it goes through various processes that result in a concentration distribution downwind of the source. An idealized picture of the concentration distribution is a plume. The relatively simple and computationally fast plume models give a “statistical plume”, i.e. a concentration distribution that represents an ensemble average over a number of individual instantaneous puffs5. For most of the early twentieth century, dispersion modelling was essentially plume modelling.
A more sophisticated method is given by a puff model, where a series of puffs are emitted from the source and their downwind growth, splitting and combining is modelled6. In the simplest case, the sequence of puffs will simply make up the plume.
Finally, an advanced dispersion methodology is the Lagrangian particle dispersion model. Thousands of individual particles are traced and their distribution gives an estimate for the concentration field. This is the most computationally demanding method. The Gaussian puff model is the most common since it is a good compromise between computational efficiency and accuracy.
Figure 5: An example puff dispersion model run in an urban environment
Conclusions
It’s impossible to give a full description of all the elements of UK CBRN WaR in this brief article. However, we have aimed to give an outline, with emphasis on areas of particular interest, to give a flavour of the current process and thinking behind this. CBRN defence is an area of on-going research, which will improve capability and ultimately help keep troops and civilians safe.
Some of the elements talked about above are clearly more appropriate for a battlefield context but many of the ideas, like OA and sensor placement, are just as applicable to a non-military environment, such as urban landscapes, sporting events like the Olympic games, transport hubs like underground stations or other areas of high population density. Of course, ideally the prevention of any hazardous release will always be a better option. For accidental releases this may be achieved through, for example, proper safety procedures and maintenance and in a military context, through diplomatic, information and economic means.
Comment on this article
Skip to Main Site Navigation / Login
