Analysis of Spinal Compression and Energy-Absorbing Seats in Blast Environments

Combat vehicle designers have made great progress in improving crew survivability against large blast mines and improvised explosive devices. Current vehicles are very resistant to hull failure from large blasts, protecting the crew from overpressure and behind armor debris. However, the crew is still vulnerable to shock injuries arising from the blast and its after-effects. One of these injury modes is spinal compression resulting from the shock loading of the crew seat. This can be ameliorated by installing energy-absorbing seats which reduce the intensity of the spinal loading, while spreading it out over a longer time.

The key question associated with energy-absorbing seats has to do with the effect of various factors associated with the design on spinal compression and injury. These include the stiffness and stroking distance of the seat’s energy absorption mechanism, the size of the blast, the vehicle shape and mass, and the weight of the seat occupant. All of these affect the spinal compression, as measured by the Dynamic Response Index. This paper presents a simple analytical model which ties together all of these variables, showing the effect of different energy-absorbing designs on crew survivability over a range of blast conditions. The analysis shows that the most important factor in determining the capability of the system to prevent injury is the stroking distance available to the energy-absorption mechanism. In addition, the analysis shows the limits of performance available to any seating system, and also how to optimize the seat design to produce minimum spinal compression for any given set of design parameters.