NIJ Standard 0106.01: This is the primary standard for testing ballistic helmets. It defines protection levels based on the ammunition threat:
Level II: Designed to stop 9mm FMJ RN and .357 Magnum JSP bullets.
Level IIIA: A higher level, designed to stop .44 Magnum, .357 SIG FMJ FN, and 9mm FMJ rounds. This is the most common level for combat helmets.
"One Hit" Certification: It's crucial to understand that certification is based on the helmet's ability to stop one round from a specified threat at a specific velocity. It does not guarantee performance against multiple hits in the same location or against threats beyond its rating.
V50 Testing: Beyond the pass/fail NIJ test, helmets undergo V50 testing. This measures the velocity at which 50% of projectiles will penetrate the helmet and 50% will not. A higher V50 score indicates a greater safety margin above the minimum standard.
Backface Deformation (BFD): Even if a bullet doesn't penetrate, the helmet material can deform inward, causing serious injury. NIJ standards set a strict limit on this inward dent (typically ≤ 25.4mm). This BFD measurement is as important as preventing penetration.
