Tensile Force Limits of the Sheep Spine: Comparison to Forces Required to Extricate Grain Entrapped Victims

Grain storage facility entrapments continue to be of concern in the agricultural industry, with nearly 1,500 documented incidents recorded over the last 45 years. Previous research studies have shown that attempting to extricate a full-size pulling test dummy from a grain mass requires a substantial amount of tensile or pull force - e.g. up to 1.32 kN if "buried" at waist depth, 2.77 kN at chest depth, and 4.01 kN at head depth. There is, however, a paucity of studies on the amount of distraction the human lumbar spine region can endure. The objective of this research study was to test the maximum tensile force that could be exerted on a sheep's spine (comparable to the human spine) before the intervertebral discs and surrounding ligament would show signs of failure.

Eight lumbar-region sheep spine segments were axially distracted using an MTS Criterion tensile testing machine, and the maximum forces were recorded.

The average maximum force that the spinal discs and ligament withstood before showing signs of failure was 2.14 kN (standard deviation of 0.31 kN). This is comparable to the force required to extricate an individual entrapped in a grain mass at chest depth.

The authors recommend that grain entrapment victims should not be forcefully pulled out if buried to waist level or above due to two primary reasons: (1) the large variation in failure load observed in our experiment with sheep spines and (2) the lack of knowledge regarding the victim's pre-existing medical condition. The extractive forces required to remove a victim of entrapment in grain overlaps with the force needed to cause potential damage to the sheep spine, as the 1.7-3.0 kN range is comparable to the 1.65-2.48 kN force range that causes axial failure in the spine.