Head protection in PPE terms is considered as protection against impact injury and some burn injuries. It generally protects the scalp area, and sometimes the jaw. The face is generally not included, except for some sports helmets. Eye and face protection, noise protection and respiratory protection are separate types of PPE. Protective clothing standards include protecting the head from chemical, biological and radioactive hazards.
Head injuries
Head injuries can be very complicated – some are obvious when the accident happens but others appear hours or days after the accident. A head injury involves different kinds of damage to the skull and its contents. This may also include neck injuries. Different types of head injury often happen in one accident.
Put very simply, the brain does not fill the skull – rather than being fixed firmly in place it “floats” inside the skull. Also, the brain and its blood vessels are soft, and can be damaged by contact with the inside of the skull and by being compressed or twisted. Obviously, if the skull is broken then the brain can be damaged by direct contact – an open head injury. But the brain can also be damaged without direct contact if it hits the inside of the skull, or is twisted on the top of the spinal cord – a closed head injury. For example, in a severe whiplash car accident there can be damage to the brain from being shaken against the skull, as well as neck injuries.
Medical research has provided a lot of useful information on the types of head injuries occurring in accidents, and how these injuries are caused. However, because head injuries can be so complicated, the exact mechanisms that cause these injuries are still not clearly understood.
When there is an impact to the head, there are accelerations and rotations of both the head and the brain inside the head. Research studies have defined the impact forces and accelerations which cause some types of head injury. These data come from a combination of accident and casualty data, and tests on cadavers, animals and volunteers. Because we are all different, our individual “head injury tolerances” are different. So, the forces and/or accelerations that are likely to cause head injuries are given as a range, and not as single values. As an example, the force to fracture the skull causing serious injury (and maybe death) is in the range 600 to 20000 N, with the typical force for a healthy 25 year old male likely to be around 3500 to 5000 N. Similarly, moderate or more severe concussion has been found to occur around 3000 N upward.
The general aims of head protection are then very simple:
- To reduce the level of the force/acceleration on the head to an “acceptable” level
- To prevent objects cutting or penetrating the head
Clearly, the important question here is what is an “acceptable” level of injury? I will return to this later.