R&D: Blast Seats

Sep 15, 2008

Combat vehicles operating in theatre face a variety of threats, including blasts from roadside bombs, mines and weapons. Historically, protection was focused on protecting the vehicle itself. Current research and resources have expanded to a field known as “Survivability Systems,” ensuring the occupants are properly protected from these and other threats, such as heat stress.

Vehicle manufacturers strive for the greatest protection possible through design and armour. However, studies have shown that the use of blast attenuation seats is ­critical to occupant survivability by reducing blast effects on the human body.

In developing these seats, research engineers have considered the major causes of human injury from a blast: acceleration, shrapnel, internal collisions and flailing. The effectiveness of a blast attenuation seat is then measured using STANAG 4569, which defines the critical injury criteria for the neck, spine and legs.

Using this data, blast mitigation seats can be validated through computer model­ing, lab and full scale blast testing, using instrumented crash test mannequins. The Flight Impact Simulation (FIS) facility of the National Research Council of Canada has been modified to simulate blast trials for these purposes. The FIS Air Cannon is used to accelerate horizontally-mounted blast mitigation seats to predetermined peak velocities and acceleration profiles.

Mounted soldiers must be protected from both phases of a blast event: the initial acceleration upward until the vehicle reaches its apex, followed by a ‘slam’ back down to the ground, potentially into a crater and without its suspension. Both phases can seriously injure the occupants.

Conventional vehicles have typically not provided a blast attenuation seat, while initial seat solutions were premised on isolating the occupant from the floor of the vehicle. These ‘isolation seats’ rely upon the design and mass of the vehicle to protect the occupant from local accelerations, but are less effective against larger blasts with substantial gross vehicle acceleration.

To deal with higher level blasts, an ‘attenuation seat’ is required, based on its ability to absorb energy. The energy load reduction is accomplished through either a one-time-use or recoverable system. A one-time-use Energy Absorbing (EA) system relies on a plastically deforming element to dissipate energy. A Recoverable Attenuation System (RAS) dissipates energy while compressing and then rebounding to the original length, ready to deal with the ‘slam down.’

With sufficient space, the one-time-use system may be able to deal with both phases of the blast. However, in most cases and especially in a retrofit ­application, space is at a premium. In these situations, the RAS-based system will provide equivalent energy dissipation but with only half the space claim.

Seating platforms that mitigate injury threats must balance with design engineering factors such as ergonomics, function and integration into tracked and wheeled vehicles – each with a unique interior. The result is that mounted soldiers, whether seated individually or on benches, now have access to highly advanced ceiling, wall and floor mounted systems.

As part of an overall design, it is imperative that the seat utilize a four or five-point harness to constrain the occupant to the blast seat. Further, the seat belts must adhere to an ‘all belts to seat’ principle, so the occupant remains safely secured as the seat moves during the blast phases.

The most effective seat solutions, as proven by military research establishments and currently deployed in Afghanistan, also offer foot pads to protect the occupant’s legs from the vehicle floor during a blast.

As vehicles reach their maximum load capacity in terms of protective enhancements, blast attenuation seats represent the next step in future survivability programs.

Todd Bosik, P. Eng., Director of Blast Attenuation Seats at Allen Vanguard, has been developing seat solutions since 1998. He can be reached at 1-613-739-9646 or todd.bosik@allenvanguard.com
© Frontline Defence 2008