Blast Mitigating Seating
Land Mines and IEDs are Dangerous For the Damage They Cause with Fragmentation but the More Critical Element is the Ability to Mitigate the Energy to Transfer of the Blast to the Seat Occupant.
by Marty Kauchak
SOTECH Correspondent
Methods of providing this mechanical isolation include things like allowing for adequate seat stroke/seat displacement relative to the vehicle and/or by incorporating other appropriate shock isolation devices between them.
Driven in large part by ongoing operational exigencies, the last half-decade has witnessed the emergence of a range of new seat designs intended to minimize of blast impulse on operators and crew of tactical vehicles around the world.
In many cases, the impulse attenuating challenges in enhancing the safety of helicopter crew during crash situations as well as high performance aircraft ejection. In some cases this overlap of challenges has allowed designers to draw on years or even decades of prior development expertise.
One example can be found in the November 2005, announcement by ArmorWorks that it had received a Small Business Innovation Research (SBIR) award from the U.S. Army Tank and Automotive Command (TACOM) “to develop a vehicle mine blast attenuating crew seat system that prevents spinal compression injuries to U.S. troops caused by landmine detonations.”
“ArmorWorks recognizes that this award only strengthens our efforts to achieve our ultimate objective, saving lives,” said Bill Perciballi, president of ArmorWorks.
“Our approach builds on existing aerospace energy attenuation designs where extensive research has been conducted on human tolerance to acceleration, particularly in the area of helicopter crashes where occupants encounter similar acceleration conditions to those of ground combat vehicles,” added the company’s chief scientist, Dr. Ken-An Lou.
In February 2007, the company introduced its ShockRide energy absorbing seating, designed to protect troops exposed to mine blast effects from spinal injuries. Seven months later, the company announced the initial order from BAE Systems to place the new seat designs into one of the company’s mine resistant ambush protected (MRAP) vehicles.
At the time of the September award, Perciballi explained, “The explosion of a mine or IED beneath a vehicle can create shock waves that are more destructive than the impact of the vehicle dropping 100 feet. We saw a critical need to develop a product that could save our soldiers, not only from ballistic fragments, but also from the extreme shock from a mine blast. Energy attenuating seats are a natural and needed addition to our line-up of life protecting products.”
The seats were installed on the BAE Systems’ RG-33, an MRAP family that includes a special operations variant.
A BAE Systems program participant recently observed that “The Armorworks squad seats, after design enhancements in the seat pan and seat frame, have proven to be extremely durable and the RG33s have had no issues to date. With the addition of the integrated footrest, Armorworks continues to deliver an extremely reliable and durable product.”
In April of 2007, Canada’s DEW Engineering and Development Limited announced that it had formed a strategic partnership with ArmorWorks “for the production and distribution of ArmorWorks proven line of proprietary vehicle survivability products in Canada, for sale to the Department of National Defence and to major prime contractors for export sales as part of Canadian Industrial Regional Benefits.”
“DEW has always believed in strategic partnering with world class firms and we are proud to team with ArmorWorks” said Timothy Dear, president DEW Engineering. “The first of many projects we are focusing on is mine blast attenuating seats. They are not in themselves a panacea against improvised explosive devices, but when installed in the right vehicle with ballistic, fragment and blast overpressure protection, they are the final link to save lives. With ArmorWorks, DEW can now offer the complete survivability package.”
But ArmorWorks is definitely not alone in the field of blast attenuating seating. Ironically, another significant player in the arena is BAE Systems itself. BAE Systems expertise is derived from its 1 August 2007 acquisition of Armor Holdings, which had previously acquired survivability specialists Simula and Schroth Safety Products.
“Simula was founded about 30 years ago,” explained Don Dutton, vice president and general manager of occupant protection systems, a business area within BAE Systems Mobility & Protection Systems (M&PS) “In an environment similar to what’s going on in the ground vehicle market, it was founded by a lot of researchers doing good work on how they could mitigate injuries and fatalities based on helicopter crashes in Vietnam. Our founder focused on seating technologies and how he could mitigate spinal and flail injuries in helicopters. So he developed some technologies that led to product development for the Black Hawk, and ultimately we became—and continue to be—the leader in energy absorbing seating for helicopters: the Army; across DoD; and in some cases commercial markets.”
“Through that time there have been some core competencies that have driven product development in a couple of different directions, he continued. “Lightweight armor, for example, because that’s a necessity in lightweight seating for helicopters. Another core competency was energy management in other types of products. We also had an evolution towards ‘system capabilities,’ where we developed, introduced, and fielded airbags for helicopters, including the Black Hawk and the Kiowa Warrior. And in nextgeneration work, we also do external airbags for the Navy’s trainer. It’s kind of a wholesale approach to energy management and crash worthiness on an aircraft that requires a stepchange in capability.”
“In terms of the ground vehicle market we have been working toward the ‘more severe environments, introducing the first blast mitigating capability into the Humvee, over 10 years ago. And we’ve done some other things with TARDEC and other OEMs relative to where they are looking for more than just a robust truck seat; where they’re looking to solve a tougher and more challenging problem. And that’s really where this market has evolved today,” he said. “
On the ground vehicle market, we’re onboard the [BAE Systems] Caiman [MRAP],” he noted. “And from a seating and / or restraint perspective, we are also on a lot of the other OEM platforms. That being said, I’m not really allowed to get into that because of disclosure agreements we have in place.”
Dutton continued, “Based on this heritage, and specific to the ground vehicle market, we really focus on how we mitigate the problem of spinal injuries due to the blast. And if you look at the problem it really is the same physics, related to a helicopter as it would to a ground vehicle. You’ve got energy coming up that potentially can be imposed on the occupant’s spine. And that is really the weakest part of the human body and the most likely injury mechanism during a vertical event helicopter crash or mine blast. So the seats are designed to basically absorb that energy through that event. Now, that being said, there’s also a lot of focus on leg injuries following the mine blast event and also the potential of impact, rollover, and other types of events that can happen subsequent to or independent of the mine blast. We also need to worry about protecting them from flailtype injuries, like you might in an automobile with head impact to the steering column, as an example.”
He continued, “At the core [of the “survivability onion”], where we are protecting the warfighter and the vehicle hasn’t been penetrated, we’ve done a good job of keeping the bad stuff outside. That being said, the internal environment is less than ideal. And you need to mitigate certain aspects of that environment for the occupant.
“The inside of the vehicle is a very severe environment and potentially very injurious or fatal without the right components and systems,” he said. “That being said, just like in aviation, we’re also looking for the right solution for the warfighter relative to human factors, comfort, and mission effectiveness. So it can’t all be about just providing that survivability package. We’re talking about part of the vehicle that they rely on to perform their mission. So those are other attributes that we need to be aware of as we do our best to address their needs.”
In terms of future company developments, Dutton avoided specifics, but offered, “If you look at the market, and it is extremely dynamic with threats increasing, we do see a convergence of technologies and products from the aviation and commercial automotive side, in terms of ‘it’s not only about seats and restraints and those components, but we’re seeing an evolution towards balance of the overall system, an advanced system potentially including airbags or ‘pretensioners,’ and the problems addressed from an integration of the vehicle capability and these internal capabilities. So it is moving fairly rapidly and we are seeing the customer interested in collaborative investment to continue to push it forward.”
He concluded, “From our perspective, it is all about the warfighters—how we can protect and safe those guys in those vehicles. The environment has been moving extremely rapidly and I think that industry is doing a pretty admirable job, given the evolution of threats. We’ve seen TACOM put out guidance and working towards requirements for these types of threats. I think that’s a great thing. And I think we’re working towards an industry understanding on how we can continue to develop the best products and set requirements for these products. Where it is done at a vehicle level today, I think it will evolve—on the aviation side there are actually specific requirements set for seating and restraints at a component level. I think [the ground side] will evolve towards that. And that’s a good thing, both from the customer and industry sides.”
Reflecting in part that “convergence of technologies and products from the aviation and commercial automotive side” noted above, Global Seating Systems LLC came into the blast mitigating seating market with a background of 20 years commercial experience.
“This has really been an offshoot or growth from some of our commercial technology,” observed Christian Hammarskjold, president of Global Seating Systems LLC. “We are the leading seat supplier in commercial extreme duty markets. When you look at things like off-road vehicles, which bounce high off boulders, or even things like a transit bus, which people kind of ignore. But take issues like potholes, combined with vehicles that are driven 20-24 hours a day by 4-6 people a day, 7 days a week, 52 weeks a year, for a 12 year life. So we have a lot of experience with severe environments; with heavy drivers—we are trying to accommodate one driver who is almost 600 pounds— and then dealing with the vertical forces of potholes or off-road conditions. So we built upon that technology, as well as developing new technologies for blast forces from IEDs and mines.”
“We got our first order in 2000 or 2001, and then we really started focusing on the military side in 2005,” he added. “Our first big order was a call from the Army, saying they were having a big problem with one of their truck platforms (M939 series 5-ton trucks) and couldn’t find a solution. They called us up. Using some of our commercial technologies we tweaked the design and fit it into a vehicle. We were successful in finding a solution for that and they retrofitted the fleet in Iraq. And that was how we really got started on a big scale with the military.”
“When we talk about blast and shock mitigating seats, we need to look at the broad considerations revolving around that,” he explained. “After all, seats are just part of an overall survival package. The seat, by itself, doesn’t do it. It’s the armor—active or passive, V-hull, exploding floors, and seats. And often we get stuck at the very tail end of a project, given a space constraint and told to put our seat into a particular envelope, which limits the technologies and designs that can be put in there. For example, if we have to put a seat on top of a battery box, there’s no room for a stroking system, and we have to have a very low-profile mitigating design. On other vehicle platforms, take the M939 for example, we have a flat floor and we have lots of room to have a stroking system. So we can put a different type of technology into that application. We also have other applications where the seats need to be wall-mounted or roofmounted. And again that requires a different kind of technology. So, having one technology is never going to work for every application. We have several different technologies that are best used in specific places on specific vehicles.”
Based on this need for design and installation flexibility, Hammarskjold said, “With our technology and experience we really consider ourselves design integrators and s u r v i v a b i l i t y experts more than seat manufacturers. We try to look at the total package: what are the envelope considerations; when so the h-points have to be; are there and vision considerations for seeing outside the vehicle; do you have to reach and pedals or electronic equipment? So it’s really designing a total solution, not just giving someone a seat and telling them to figure it out.”
Hammarskjold also highlighted the importance of addressing impulse forces from multiple quadrants.
“Seats need to address more than just shock and blast mitigation,” he said. “And we see such an emphasis on the Z-axis, which is the vertical axis. But the fact is, take a Humvee for example, with the increased weight of a Humvee and all the rollover problems they’re having right now, seats need to be part of the solution for rollovers. The MRAPs are much more effective than the Humvee at mitigating blast but they have a very high center of gravity, so rollover issues with MRAPs need to be addressed by seats. With convoys, we have long supply lines between Kuwait and Baghdad, and we’ve seen a lot of convoy accidents, which mean frontal as well as rear impacts. So seats need to be tested to accommodate what we call X-axis, or front to back impacts. IEDs often deliver a lateral impact so we need to test our seats to lateral forces, which we cal the Y-axis.”
He continued, “Then, it’s very important too when we talk about blast to remember that it is really a two-phase event. It’s the blast followed by the ‘slamdown’ event. So testing to just one specific pulse is not reflective of what actually happens. So we think there’s a lot of opportunity with the current deigns and current technology. We think we’re doing better on it and we’re focusing our company on improving further. Some of our technologies right now are actually a ‘recoverable’ design, so after the vehicle has a blast event, the seat will stroke down and then reset itself to protect the occupant from the ‘slamdown’ event. So that’s a big focus of all of our technology—not a single phase event or a single stage technology but a dual phase recoverable, variable energy attenuator.”
Hammarskjold also highlighted the importance of warfighter body profile in reducing blast injuries.
“Most current technology is focused on the technologies of the blast mitigation system,” he said. “It is very, very important to understand that seats need to be designed with the occupant and the environment in mind.
“Soldiers wear body armor. They’re wearing ammo. They have Camelbacks. They have radios. They’re wearing 100-plus pounds of equipment and that radically changes the body profile. And once you have a Camelback on, for example, you actually get pushed forward on the seat. So any support that seat has been designed to give you is lost, because you’ve lost the contact of the seat to the occupant.”
The significance of that warfighter posture issue was highlighted in a 2007 report from U.S. Army Research Laboratory [“Shock Isolation Parameters Based on a Damped Harmonic Oscillator Model for Mine Blast Protected Seating,” by Brendan McAndrew, ARL-TR-4236, September 2007]. In describing how the Dynamic Response Index (DRI) model can be used to explore the implications of blast mitigation for potential spinal injuries, the ARL report stated, “It should be emphasized that this model only considers vertical accelerations, and that injury rates rise when the acceleration vector is more than 5 degrees from vertical.”
Hammarskjold took a similar track, noting, “We are unique, with the removable Camelback, removable side pouches, and removable side bolsters. People sometimes think that it’s a gimmick but it’s actually hugely important to survivability. Because body posture and correct spinal alignment is directly correlated with maximizing injury thresholds. The minute we lose body posture and good alignment our injury thresholds are actually dropped. So our seats are designed for the soldier; to fit his equipment. You can remove the Camelback pouch and move your back further in. You can take the bolsters off so you can get your body properly seated and get good geometry between the seat and the occupant. And with the proper posture and proper alignment, not only is the soldier more comfortable but he is also now well coupled to the seat and can maximize his injury threshold. And we’ve got a bunch of patent pending designs on our seats right now with the ‘Cobra’ [seat system] serving as the epitome of that design philosophy.”
Further highlighting Cobra as “a modular seating system.” he acknowledged, “As much as I want to say that one seat will fit into every single vehicle, the reality is that each vehicle has a unique space profile and constraints. So we have a very modular system that can be configured in different ways to fit into different positions within the vehicle. Think about a driver / commander’s seat. They need to adjust front to back. They need to adjust up and down. We need to concern ourselves with reaching pedals and steering wheels. We need to accommodate 5th percentile females as well as the very large males. We need to provide access to dashboards and controls. And that’s a very different type of seat than we would potentially need on the back of the vehicle, where it may be a wall-mounted or ceiling-mounted seat or it may be laterally facing. So we have designed a product line that really can be put anywhere in the vehicle.”
Israel’s Plasan is another company currently fielding blast mitigating seat designs.
According to company representatives, the Plasan seat designs lack specific marketing/trade names, “since the seats were developed to increase our systems performance in terms of survivability and were not promoted as standalone items.”
Two versions of the seats are currently available: suspended seats and blast mitigation seats.
The suspended seats are described as “fully floating, supported by a high strength, high tension fiber rope anchored to multiple points on the roof and floor—or sides—of the vehicle. The seat is equipped with a foot rest and a head rest that extends from the seat. This design fully isolates the seat from the floor and hull, thus protecting the occupant from the extreme vertical accelerations caused by the blast effect. The seat design is flexible, and customizable to any given vehicle, for example, the placement of the anchoring points is dependent upon vehicle specifications.”
Highlighting the fully suspended system as “The best protection against mine blasts,” developers pointed to features like: flexibility of attachment (allowing simple customization—seats are vehicle independent); ease of installation and usage; a continuous rope system controlled by easy ratchets, enabling simple and fast adjustment of tension and seat stability; and a variety of seat designs available to provide for a variety of customer needs.
“Plasan seats were developed as a survivability item to complete our 3 level blast mitigation concept,” the spokesperson said. “It is all about survivability—we have test reports showing outstanding performance in respect of lowering the accelerations that affect the occupant in a blast event. In addition, comfort is another aspect that represents our approach in design—human engineering. The seats include cushions that not only assist in reducing the acceleration but also provide great comfort for the user. The seats can be folded and easily attached and removed.”
In describing the blast mitigation seat options, company representatives noted, “In this method the original OEM seat is kept and a box is actually assembled beneath it. The box has a collapsing mechanism that absorbs the energy in the event of blast. The collapsible seat base is designed to absorb the vertical accelerations experienced in a mine blast and thus reduce both the explosive forces and after-blast effects inflicted on the passenger. The collapsible seat base is a rigid box, which remains stable under normal driving conditions, including off-road, and can only become active under extreme circumstances, such as an explosion. The base is activated by the use of shear pins, which respond only to violent vertical forces, and utilizes aluminum foam and stainless steel springs as energyabsorbing elements. The absorption of the vertical accelerations experienced in a mine blast and the reduction of both the explosive forces and after-blast effects is accomplished by a downward motion of the seat base during the collapse stage.”
The design allows the upgrade of existing vehicle seats to blast resistant seats while retaining their original features (e.g. movement up, down, forward backward).
Plasan is currently fielding its suspended seats on the Navistar MaxxPro and the recent MaxxPro Dash, and its blast mitigation seats on the Oshkosh MTVR [Medium Tactical Vehicle Replacement] and LVSR [Logistics Vehicle System Replacement] vehicles.
Summarizing warfighter benefits, a company representative offered, “The Plasan suspended seats demonstrate significant advantages over any known seat fixed to the floor with or without a collapsible base. Additionally, compared to other suspended seat solutions, the Plasan continuous rope system allows multiple attachment points to the vehicle roof, sides or floor, thus providing ease of adjustment and tension. The seat was designed to comply with ergonomic requirements as described in MIL1472-F tables.”
When asked about new designs in the future, they acknowledged, “Since we have feedback from the warfighter on our seats from theater, we can create a concept that will include all lessons learned— easy access to storage behind the seat, head and foot rest design and functionality, enhance egress capability and of course there is always room to increase survivability.
“One of our major guidelines is commonality,” they added. “We wish to create a solution that will be relevant to an MRAP version and to a HMMWV.”
Other companies are involved in blast mitigating seat designs. Autoflug, for example, offers safety seats for land craft “based on more than 10 years of experience gained from safety seats for helicopters.”
Allen-Vanguard, provides another recent example, offering a bolt-in blast protection seat design that “increases human survivability to the driver and passengers by isolating the occupant, thereby protecting the brain, neck, spine and lower legs.”
Other seating examples can be found from companies like Australia’s Stratos, whose BattleSafe Range seating designs offer multiple options for mine blast resistant seating configurations.
As noted by several participants in the field, one of the most significant emerging trends in blast mitigation seating involves the benefits derived from government participation and seating considerations much earlier in the design process. This totality of systems approach enhances the multiple benefits derived from the survivability onion.
Meanwhile, the Jankel Group of the United Kingdom has announced that it is establishing an assembly and manufacturing facility, Jankel Tactical Systems (JTS), in South Carolina. Working with local industry, JTS will be capable of low-rate initial production of its life-saving mine blast attenuation system. The Jankel Blast Attenuation Seat (J-BAS) and Pulse Attenuation Device (J-PAD) were developed in response to a requirement from the UK Ministry of Defence (MoD) to enhance the survivability of personnel operating on light wheeled vehicles in an environment where there was a high risk of attack by mines and IEDs.
The equipment recently entered service with the UK MoD on the Jackel patrol vehicle and already is credited with saving lives and reducing the severity and incidence of injuries.
The U.S. facility will create employment and enable the on-shore supply of this innovative technology to the U.S. military with the company objective of becoming the preferred supplier of choice for mine blast attenuation seating systems for use by the U.S. home market.
The Jankel Group currently is investing significant engineering effort and resources into developing a range of blast mitigating seats and survivability systems based on the core components of the J-BAS and J-PAD. It now has available a ‘heavy’ variant optimised for armoured personnel carriers, such as the British Army Bulldog (uparmoured FV432 (armored personnel carrier), the M113 and the LAV. Earlier this month Jankel were advised that J-BAS has been selected by UK MoD for the JCB high mobility engineering excavator and the modified vehicle will enter service in early 2009. This version of J-BAS has integral suspension and so is suitable for trucks as well as engineering equipment.
Perhaps the best recent examples of this trend can be found in the currently open solicitation for the Joint Light Tactical Vehicle (JLTV) [Solicitation W56HZV-08-R-0210].
In addition to specifying contractor modeling parameters for the armored structures themselves, the solicitation mandates, “The contractor shall perform mine blast analysis for each deliverable subconfiguration at each contractor defined protection level. The contractor shall model the vehicle system comprising the wheel/tire assembly, chassis, suspension, engine, transmission, and internal components of the seat, restraint system, steering wheel/column, and interior cab area that may interact with an occupant in a blast event. The contractor shall provide model inputs comprising the material properties, assumptions used to model event, models/simulation, and model results for the driver, passenger, crew acceleration data as identified in ITOP 4-2-508. The contractor shall provide model results for system performance by identifying cab/hull deformations or breaches located at the crew feet/pedal location, center of the cab, passenger feet location points, and seat connection points. The contractor shall provide acceleration profile for the vehicle system from the blast event location through the center of vehicle to the passenger area…” ♦