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FAQs > Zylon®-based Body Armor

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Has the cause of the Forest Hills (PA) vest failure been determined?

NIJ has performed a statistic-based series of ballistic tests on artificially-aged armors in an effort to determine the cause of the Forest Hills, Pennsylvania, incident in which a unit of NIJ-compliant body armor failed to prevent penetration from a bullet it was designed to defeat. These armors were artificially weakened to match the condition of the rear panel of the Forest Hills officer's armor. No penetrations occurred during this testing, so NIJ cannot draw any definitive conclusions at this time regarding the cause of the failure.

Through tests and research conducted to-date, several factors have been identified that may have contributed to the failure:

  1. The front panel of the officer's armor-not available for analysis because it was needed as evidence for the criminal prosecution-may have been significantly weaker than the rear panel. Thus, the aged armors may not have been accurately representative of the panel that failed.
  2. NIJ relied on tensile strength as an indicator of ballistic strength.other mechanical properties might also influence ballistic strength.
  3. Bullets might be more likely to penetrate regions of mechanical damage caused by folding, flexing, abrasion, etc.
  4. The moisture content in the interior of the officer's panel at the time of the incident is unknown. The presence of moisture in an armor panel can influence ballistic resistance.

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