Methodologies for Blunt Trauma Assessment in Military Helmets

Since World War II, U.S. military combat helmets have provided various degrees of protection against ballistic threats, including fragments and bullets. Only recently, however, have combat helmets been specified to provide blunt impact protection. This study assesses the current generation of combat helmets and four commercial off the shelf (COTS) pad suspension systems (denoted A, B, C, and D) for blunt impact protection against realistic blunt impact threats including falls, parachute drops, and motor vehicle crashes using a drop test methodology based upon the Advanced Combat Helmet (ACH) Purchase Description (CO/PD-05-04) and the U.S. Department of Transportation (DOT) Laboratory Test Procedure for Motorcycle Helmets (TP-218-06). Three variant headforms (DOT, NOCSAE, and ISO) and three independent testing laboratories were used to examine 549 helmet samples with a total of 7,686 impacts. A single ballistic shell manufacturer was used to reduce potential variability. All five fielded helmet sizes (S, M, L, XL, and XXL) were included in the study, and impacts were conducted at three temperature conditions (263±5°K, 295±4°K, and 327±5°K) as well as at three impact velocities (3.0±0.1m/s, 4.3±0.1m/s, and 5.3±0.2m/s). For the DOT headform tests, hot temperature conditions showed substantially greater peak acceleration than the cold or ambient conditions (~60g across all tests). Peak acceleration values from the first DOT headform impact averaged 30g less than those measured during a repeat impact. On average, the peak impact accelerations measured in the NOCSAE headform were 48g less than those measured in the DOT headform and 74g less than those measured in the ISO headform, across all velocities. As the impact velocities increased, this effect became more pronounced. Careful consideration should be given to advantages and disadvantages of each test headform for future testing. Detailed headform anthropometry may be an issue for assessment of higher performance helmets and should be further evaluated.