How Do Bulletproof Helmets Protect Against Blast Waves?

Understanding Traumatic Brain Injury (TBI) from Blast Waves

Traumatic brain injury (TBI) on the battlefield is mostly caused by exposure to shrapnel impact and blast waves.
In recent years, the frequency of the use of flammable and explosive materials has increased, which has also increased the frequency of blast traumatic brain injury (bTBI) among soldiers and the public.

To explore the impact of bulletproof helmets and liner systems on the biomechanical response of the brain under dynamic shrapnel and blast loads, we need to have a deep understanding of the mechanism of TBI and the brain damage threshold.

How Bulletproof Helmets Absorb Impact and Blast Waves

During shooting, part of the kinetic energy of the penetrating bullet is consumed in the helmet rupture process. Part of the blast wave is reflected when it reaches the head, while other parts penetrate the skull and enter the brain.

If equipped with a liner, a large part of the impact energy will be dispersed. This is because when shrapnel hits, it will form stress waves, pressure, and movement in the helmet, skull, and brain, which may damage brain tissue.

The Role of the Liner System in Bulletproof Helmets

The liner system is a key component of the combat helmet. The use of helmet liners made of energy-absorbing materials can significantly reduce the amount of load transmitted. Among them, foam is often used to make helmet pads as an energy-absorbing material.

Foam materials can withstand significant compression deformation to absorb a lot of energy and reduce energy by bending, buckling, or breaking foam units. The padding actually depends largely on the shape, structure, and system configuration of the material.

Structural Characteristics of the Padding System

The padding system must meet the following structural characteristics:

• It must contain multiple components and be easy to install and remove so that the wearer can adjust it properly.

• Typically, one circular pad, two trapezoidal pads, and four oval pads are used, designed in two thicknesses: ¾ inch and 1 inch.

• The padding must meet three key functions:

1. The inner fabric in direct contact with the wearer's head for moisture absorption.

2. The padding layer that provides comfort and protection.

3. The outer fabric adhered to the helmet.

The padding system is designed to provide spacing, comfort, safety, and stability.

The hook plate is fixed to the inside of the safety helmet by adhesive to provide an attachment point for the outer fabric. A sufficient number of hook plates are required to support the movement of the pad, and at least ½ of the area inside the helmet shell should be covered with hook plates. Each liner system has a label indicating the liner thickness and other production details.

Performance Requirements of the Liner System

The liner system must meet the following performance requirements:

1. The outer fabric should be made of a material that can adhere to the inside of the helmet shell and have a specified peel strength (3.5 pounds per inch of width).

2. The liner material must be able to be compressed repeatedly without failure and be vibration resistant.

3. The hook plate must be strong enough to resist falling off the inside of the helmet shell and have sufficient peel strength (3.5 pounds per inch of width).

4. The liner must not fall off the helmet during buoyancy testing.

5. The color of the inner and outer liners should meet the specified standards.

6. The liner should remain intact in a temperature range of -60°F to 130°F and at an air pressure of 15,000 feet above sea level.

By integrating these structural and performance characteristics, bulletproof helmets enhance protection against blast waves and reduce the risk of traumatic brain injuries.

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