Estimating Passive Stress Acting on a Grain Entrapment Victim's Chest

Grain entrapments remain a major concern in the grain industry, with 1,100 incidents documented since the 1970s. One particular concern is the ability of a victim to breathe while entrapped in grain. Anecdotal reports suggest that victims struggle to breathe when entrapped in grain to a depth that covers their chests, yet some evidence indicates that victims should be able to breathe normally as long as their airways are not blocked regardless of depth. The hypothesis for this discrepancy is that previously published experiments measured an active stress state in the grain, while a person breathing also experiences a passive stress state during inhalation. The passive stress is significantly larger than the active stress. The objective of this study was to measure the passive stress when pushing against grain, such as during inhalation, and compare it to active stress state measurements. An MTS Criterion testing machine, which is a force deformation testing device, was used to push a block horizontally against a column of grain and record the force and displacement during the movement. The measured passive stress was calculated from the force and displacement values and ranged from 9.4 to 11.0 kPa at a depth of 20 to 30 cm. These values are three to four times larger than previously published measurements of stresses at similar depths. This result indicates that the discrepancy between experimental results and anecdotal reports is most likely due to the type of stress state experienced in grain entrapment. Findings imply that the pressures on the victim's chest during entrapment are sufficient to cause breathing difficulties or crush/positional asphyxiation in some cases. A full-scale study is recommended.