A Reassessment of Ballistic Helmet Performance Metrics Ballistic helmets have long been a cornerstone of officer protection in both military and law enforcement settings. However, the criteria used to evaluate helmet performance may be due for a significant update. This bulletin suggests the industry challenge the traditional emphasis on Backface Deformation (BFD) and advocate for a shift toward metrics that better reflect real-world survivability—namely, penetration resistance and V50 ballistic thresholds.
Backface Deformation (BFD): A Useful but Limited Indicator
BFD measures the depth of helmet deformation on the interior surface when struck by a non-penetrating projectile. Historically, this metric has been used to estimate the risk of blunt trauma to the skull and brain. The commonly accepted threshold is 25.4 mm (1 inch), based on the assumption that deeper deformation increases the risk of injury.
While BFD remains a relevant factor in helmet design—particularly for reducing concussive injuries—it is not the most critical determinant of survival. We have seen no documented case of a law enforcement officer dying from BFD-related trauma when the helmet successfully prevented penetration. This suggests that while BFD can inform TBI prevention, helmet ergonomics and comfort, it should not be the primary benchmark for ballistic protection and ultimately, survivability.
Penetration Resistance: The Primary Survival Factor
The most compelling data comes from a 2018 Department of Defense study that examined 77 combat helmets struck by small arms fire. The results were unequivocal:
This finding underscores a fundamental truth: penetration resistance is the most critical factor in helmet survivability. Helmets that stop bullets—even if they exhibit higher BFD—are far more effective at saving lives than those that merely minimize deformation.
There are also countless real-world examples, such as a U.S. soldier who survived a 7.62 mm round to the head thanks to a helmet that prevented penetration. He returned to duty with only minor injuries, reinforcing the life-saving value of robust ballistic resistance.
V50 Ballistic Threshold: A More Comprehensive Metric
The V50 rating represents the velocity at which a projectile has a 50% chance of penetrating the helmet. It is a statistical measure that reflects the helmet’s ability to resist a range of ballistic threats, including handgun rounds, rifle fire, and fragmentation.
Unlike BFD, which is a single-point measurement, V50 provides a broader picture of ballistic performance. Helmets with higher V50 ratings are more likely to stop high-velocity projectiles, making them more suitable for modern tactical environments.
However, the articles note that V50 standards vary across testing protocols:
This lack of standardization can make it difficult for agencies to compare helmets across manufacturers. Still, V50 remains a more predictive and practical metric for evaluating helmet effectiveness in real-world scenarios.
Conclusion
The traditional focus on Backface Deformation as a primary safety metric is increasingly being questioned. While BFD remains a useful design consideration and is important, it is penetration resistance—and by extension, V50 performance—that most directly correlates with officer survival in ballistic incidents.
As law enforcement agencies continue to modernize their equipment, it is essential to align helmet evaluation criteria with the realities of the field. The evidence is clear: helmets that stop bullets save lives.
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