Hostile Vehicle Mitigation is the umbrella term to cover a range of technologies, such as bollards and barriers, for stopping vehicles and the design and procedural changes that influence the speed and direction of potential attacks to make them less effective.
A lot of the existing technology, procedures and guidance for Hostile Vehicle Mitigation (HVM) was put in place to prevent Vehicle Borne Improvised Explosive Devices (VBIEDs) from getting too close to a target of perceived value to the perpetrators. The VBIED is a well established tactic and if large enough, effective perimeter control might not be enough. This was the case with the bombing of the Marriott in Islamabad in 2008. Although the damage was extensive, principally from the resulting fire, the effects would have been more serious in the immediate short term if the device had been able to breach the perimeter and get close to the building. Blast overpressure decays quickly with distance, so any and all efforts to maintain stand-off from explosive devices should be encouraged
More recently there has been a development in the use of vehicles by terrorists and that is making the vehicle itself the weapon. This is a ‘low tech’ approach, much easier to organise and much harder to detect during the planning phase. It has however, proved to be effective with very high profile attacks on the Nice Waterfront, a Berlin Christmas market and Borough Market in London to name a few. In these attacks the targets were not fairly obvious, high profile, Government or military installations, but congregated groups of people. This has caused the authorities to think much wider on how to apply HVM measures in general and specifically for planned events where crowds are anticipated
Some Physics
Everyone has an inherent understanding that a large, heavy vehicle moving at speed is a danger. What would increase that danger more, a heavier vehicle or greater speed?
Looking at Kinetic Energy and starting with a 2 tonne vehicle at 10 metres per second:-
KE=1/2 x 2000 x 102 = 100,000 J (100kJ)
Twice as heavy?
KE=1/2 x 4000 x 102 = 200,000 J (200kJ)
Or twice as fast?
KE=1/2 x 2000 x 202 = 400,000 J (400kJ)
This demonstrates the importance in stopping or radically slowing the speed of any given vehicle. The clip below is from an old UK Government safety campaign, but we when we consider ‘Vehicle as a Weapon’ attacks its message on survivability is most appropriate.
Defining the Threat
The commercially available HVM equipment, be it blockers, gates or fences is rated to certain level (more of which later). To purchase and install the appropriate level of equipment it is important to establish the threat. This is achieved through a Vehicle Dynamics Assessment (VDA). A lot of good work has been performed by various national authorities, which has been combined with open source information to map out the performance of different vehicle classes in terms of acceleration, cornering speeds, maximum speeds etc. This information can be used to be set against the road layout, terrain and constrictions such as kerb heights and street furniture on the possible approaches to your perimeter. The most effective VDA uses a combination of plans and actual site survey where possible. For new builds this might be constrained to a paperwork exercise but does give the chance to influence the control over vehicles at a much earlier stage.
It is also the case, that despite the comprehensive efforts so far, there will factors such as specific gradients that are not covered. In such cases it is possible to carry our practical tests with the perceived threat vehicle at the correct mass and see what speed is achievable.
It is important to remember that when undertaking a VDA, the normal rules of the road do not apply. Traffic lights, lane markings, correct side of the road, pedestrian zones, pavements and one way systems are to be ignored. Events have ably demonstrated that the driver of such a vehicle is not worried about his wellbeing or mid to long-term life expectancy. The driver is certainly not worried about preserving the paintwork on his vehicle or any other damage that will affect its future resale value.
Tools of the Trade
To create your vehicle resistant perimeter and fit it with capable entry points, there is a wide range of commercial offerings available. Rather than just purchasing equipment piecemeal, it is most important that you are working to create a joined up, mutually supportive system with consideration for a carefully defined threat, capital and ongoing costs, the practicalities of installation, and the skills and personnel required for operation and maintenance.
The earlier bollards, blockers and barriers were based on heavy structures, deeply anchored. They were effective, but the scale of the engineering and depths required were expensive and created issues with other buried infrastructure. In city centres and other complex environments, there are often active or legacy underground services and cables that have not been accurately mapped. Countering this issue has been a major design driver towards shallow or even surface mount systems that disperse energy more laterally.
The examples below illustrate the many ways in which the same objective can be achieved. Each has their own particular advantages and drawbacks.
Gates:
Blockers:
Bollards:
Barriers:
Fences:
Walls:
Street Furniture:
The Existing Terrain:
Vegetation:
Temporary and Surface Mount Solutions:
Standards and Testing
It is of huge benefit to the authorities, manufacturers and customers to have a common language with which to define and compare the performance of different protection measures. In the same way that such a process has been used for body armour or blast resistant glazing, it has been applied to HVM equipment. Initially, and after much thorough research work, the performance and test standards were encompassed in PAS68/69.
This shared a lot in common with work performed in the USA and it was therefore logical that there would come a harmonisation to the benefit of all concerned.This was achieved through IWA-14 and all new equipment is tested against this standard. Older, and still viable designs, tested against the earlier documents do not need to be retested.
Understanding Test Results
A vehicle impact test gathers a lot of information and the user needs a means to readily understand these results and compare the various options. To assist in this process a performance summary format has been defined which captures the key points.
The table on the right covers the performance summaries for a range of shallow mount bollards – all of which might be candidates for the same customer requirement.
Bespoke Solutions
There are times when it is not possible to create a perimeter that gives you any stand-off for an IED or vehicle impact. In this instance your front wall or façade becomes your first, last and only line of defence. For this situation a bespoke design is required so that the outer wall stops the vehicle whilst carefully balancing the distance the vehicle penetrates and the amount of energy transferred into building through such a rapid deceleration of a large mass.
One case study in which we were involved required a low wall and a 7.2 tonne vehicle moving at 40mph. We worked with established partners to use Finite Element Analysis (FEA) to examine the effects of different combinations of steel rebar reinforcement. Adjusting the permutations of steel rod diameters and the spacing between them allowed for fine tuning of the design.
The first step was to look in general terms at the energy involved in decelerating the vehicle within a distance acceptable to the customer.
This information was then employed to produce the first iteration of an internal reinforcement pattern of steel rods that could be manufactured as a sub-assembly and in the future tested according to IWA-14
The internal reinforcement structure was tuned to so that the transmitted force into the floor slab was constrained to the acceptable limit, whilst intrusion through deflection was limited. This had to be achieved with steel bar sizes and distribution that could actually be manufactured and installed.
Success – but now what?
The day an attack is stopped at a perimeter is a win for the security team and the company or organisation concerned. From that point onward it is a race to reset the situation and overcome any of the disruption caused by the event. The longer the disruption continues, the less of a win it actually was. Before very long at all, questions will be asked from above as to why this was not anticipated and accounted for in the planning process. The questions below should be considered during the design phase to help manage the actual attack and just as importantly, the aftermath.
- Do you have another working entrance?
- Does it provide the same degree of protection?
- Does your barrier system still work?
- What is the repair/ replacement time?
- Do you have a plan for clearing the debris?
- Do you an evacuation/ invacuation plan?
- Do you have a security staff retention/motivation plan?
- CCTV capture/ witnesses/ photographs?
- Think – Business Continuity!
Owning your Hostile Vehicle Mitigation System
You have a high value item of critical equipment – it needs to work first time and every time. It may use electrics, pneumatics, hydraulics and have complex controls – will it last the course? Do you carry the right spares, have staff with the correct level of training and a suitably responsive service and maintenance contract? The equipment might not have been designed with your particular environment and climate in mind.
At SJH Projects, we and our associates would be happy to assist in your Hostile Vehicle Mitigation issues, including Vehicle Dynamics Assessments and impartial advice on equipment selection and options. Contact us Here
