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July 13, 2019
In a time of rapid technological development it is easy to forget that you have a very powerful portable computer with you all the time - your brain
Unfortunately, just like a portable computer, your brain is fragile and its packaging is not strong enough to protect it from all shocks or impacts. So, you need to choose appropriate protection for your brain and head.
Head injury is still one of the most common causes of fatal injury in accidents. Choosing the right head protection, and then using it correctly, is not that difficult and will protect both your health and your wallet.
This article gives an overview, including some of the aspects of head protection that are not so well known. The same principles of head protection apply wherever you are in the world, but I have used examples of European standards. As with any PPE, you can get detailed advice from manufacturers, suppliers and safety organizations and regulators; HSE in the UK 1 .
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 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.
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.
There are two key mechanisms:
Some of the energy of an impact is absorbed by the head protection which reduces the force/acceleration sustained by the head
The duration of the impact is increased so that, for the same energy, the maximum force/acceleration on the head is lower
In simple terms, head protection will act like the crumple zone on your car. It absorbs some of the energy and spreads out the time of the impact. High speed video of a hard hat during impact shows the helmet looking very like a jelly - it wobbles and deforms, which absorbs energy. Of course, head protection must also be strong enough to protect the head from penetration. And, just like the crumple zone on your car, head protection should be replaced after an accident!
Head protection generally falls under the same regulations as other PPE - in the UK this is The PPE at Work Regulations 1992 2 and The PPE Regulations 2002 3 . Some key points of these regulations are:
Head protection should only be used after a risk assessment has been made
Head protection should be selected, used and maintained correctly
Head protection should be CE marked (to show that it meets the essential safety requirements of the PPE Directive 89/686/EEC)
Correct selection, use, care and maintenance is essential for you to get the best performance from your head protection. All head protection should come with full instructions, and the manufacturer or supplier can provide more information. You should always follow the manufacturer’s instructions.
There may be other specific national regulations that require head protection. In the UK the Construction (Head Protection) Regulations 1989 and Docks Regulations 1988 both require suitable safety helmets to be worn where there is a foreseeable risk of injury to the head.
As for all sensible risk management, you need to assess the hazards and risks and take steps to reduce the risks until they are “as low as is reasonably practicable” (ALARP). Because head protection only protects the wearer and does not remove the hazard it is the last line of defence. Before choosing PPE you should try to remove the hazard or make the hazard less severe. For example:
Try to avoid having walkways underneath work areas where something might be dropped
Try to close off work areas above the ground so that nothing can drop from them
Create exclusion areas where there is heavy lifting overhead Most importantly, remember that head protection does not offer 100% protection against all hazards - it only protects against defined hazards and only reduces injuries to an acceptable level.
You may often see standards referred to, but do you know what they do?
Just like other PPE, most head protection is CE marked against the requirements of a harmonized CEN standard. Meeting the requirements of a harmonized standard means that the essential requirements of the PPE Directive (89/686/EEC) have also been met, and the CE mark will be accompanied by the relevant standard number. Standards also offer the advantages of:
Setting a specification that manufacturers, regulators and consumers can use
Giving a defined minimum protection performance so that products can be easily compared
Head protection standards set performance requirements for the:
Resistance to penetration (by a sharp object)
Shock absorption during impact
Retention on the head
Markings and information for the user
Specific requirements for each type of head protection
Comfort and wearability issues are not very well addressed in current standards. One of the major reasons for this is that it is very difficult to devise objective tests to measure such subjective factors. However, work continues to improve head protection standards ability to address comfort. For example, tests that would measure the ventilation of the head when wearing head protection are being researched, as this could be used as an indicator of likely thermal comfort for comparing head protection.
As I said before, head injuries can be complicated, and the exact mechanisms that cause injuries are not understood. So, how do standards writers define test methods and performance requirements?
All tests are conducted with the head protection mounted on an artificial test head.
Penetration tests are easy - a sharp object hitting the head protection with a given energy must not touch the test head.
Shock absorption tests are more difficult. A blunt object hits the head protection (on a test head) with a given energy. Different shapes of blunt object are used according to the likely hazard e.g. a kerbstone shape is used in some motorcycle helmet standards. For standards where a falling object is the main hazard, the object falls onto the head protection. For standards where the wearer falling over is the main hazard the head protection plus test head falls on the object. Either way, a limit needs to be set on the force/acceleration transmitted to the test head when the helmet is worn: this limit is intended to correspond to an acceptable level of injury. Setting this limit which is difficult, and requires the standards writers to use existing medical knowledge and experience of how head protection performs in use. At the moment, limits on the linear force or acceleration transmitted to the test head are used for shock absorption performance.
This depends on what the injury would be without head protection.
If the injury without head protection is a bump on the head or a cut, then acceptable injury is probably no more than a mild headache (e.g. the industrial bump cap)
If the injury without head protection is a skull fracture and/or moderate brain injury, then acceptable injury is probably no more than concussion and bruising (e.g. the industrial safety helmet)
If the injury without head protection is a major skull fracture and/or serious brain injury which could be fatal, then acceptable injury might be as high as minor fractures and mild brain injury (e.g. the motorcycle helmet)
Head protection standards have an introduction including words like “the protection given by a helmet depends on the circumstances of the accident and wearing a helmet cannot always prevent death or long-term disability.”
This emphasizes again that head protection does not offer 100% protection. And, for head protection just as for other PPE, increasing the level of protection means heavier and bulkier equipment which may make working difficult and introduce its own hazards such as thermal discomfort or musculo-skeletal problems.
A brick drops from the second floor and hits a worker wearing an industrial safety helmet. If the brick weighs 1 kg and drops 5 m before impact then it has an energy of roughly 50 J. The helmet standard uses a 50 J impact for shock absorption, so the helmet should protect the worker from no worse than concussion and bruising - the intended acceptable injury. Replace the brick with a pallet of 50 bricks dropping from the same height. The impact energy is now about 2500 J.
This is well above the energy used to test for shock absorption, so the helmet is no longer in its tested performance zone. The helmet will reduce the severity of the impact and the level of injury, but by an uncertain amount. If a 2500 J impact lasts 0.1 s then the force is roughly 5000 N. Without a helmet this is enough to fracture the skull causing severe injury or death. Even with the helmet this is likely to be a major injury, maybe still fatal.
This is why you should create exclusion areas where there is heavy lifting overhead - head protection is not designed to protect against very heavy falling objects.
Unfortunately, just like a portable computer, your brain is fragile and its packaging is not strong enough to protect it from all shocks or impacts. So, you need to choose appropriate protection for your brain and head.
Head injury is still one of the most common causes of fatal injury in accidents. Choosing the right head protection, and then using it correctly, is not that difficult and will protect both your health and your wallet.
This article gives an overview, including some of the aspects of head protection that are not so well known. The same principles of head protection apply wherever you are in the world, but I have used examples of European standards. As with any PPE, you can get detailed advice from manufacturers, suppliers and safety organizations and regulators; HSE in the UK 1 .
Why is head protection important?
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:
Clearly, the important question here is what is an “acceptable” level of injury? I will return to this later.
How does head protection reduce the level of the force/acceleration on the head?
There are two key mechanisms:
In simple terms, head protection will act like the crumple zone on your car. It absorbs some of the energy and spreads out the time of the impact. High speed video of a hard hat during impact shows the helmet looking very like a jelly - it wobbles and deforms, which absorbs energy. Of course, head protection must also be strong enough to protect the head from penetration. And, just like the crumple zone on your car, head protection should be replaced after an accident!
Regulations and sensible risk management
Head protection generally falls under the same regulations as other PPE - in the UK this is The PPE at Work Regulations 1992 2 and The PPE Regulations 2002 3 . Some key points of these regulations are:
Correct selection, use, care and maintenance is essential for you to get the best performance from your head protection. All head protection should come with full instructions, and the manufacturer or supplier can provide more information. You should always follow the manufacturer’s instructions.
There may be other specific national regulations that require head protection. In the UK the Construction (Head Protection) Regulations 1989 and Docks Regulations 1988 both require suitable safety helmets to be worn where there is a foreseeable risk of injury to the head.
As for all sensible risk management, you need to assess the hazards and risks and take steps to reduce the risks until they are “as low as is reasonably practicable” (ALARP). Because head protection only protects the wearer and does not remove the hazard it is the last line of defence. Before choosing PPE you should try to remove the hazard or make the hazard less severe. For example:
Head protection standards
You may often see standards referred to, but do you know what they do?
Just like other PPE, most head protection is CE marked against the requirements of a harmonized CEN standard. Meeting the requirements of a harmonized standard means that the essential requirements of the PPE Directive (89/686/EEC) have also been met, and the CE mark will be accompanied by the relevant standard number. Standards also offer the advantages of:
Head protection standards set performance requirements for the:
Comfort and wearability issues are not very well addressed in current standards. One of the major reasons for this is that it is very difficult to devise objective tests to measure such subjective factors. However, work continues to improve head protection standards ability to address comfort. For example, tests that would measure the ventilation of the head when wearing head protection are being researched, as this could be used as an indicator of likely thermal comfort for comparing head protection.
Standards test methods
As I said before, head injuries can be complicated, and the exact mechanisms that cause injuries are not understood. So, how do standards writers define test methods and performance requirements?
All tests are conducted with the head protection mounted on an artificial test head.
Penetration tests are easy - a sharp object hitting the head protection with a given energy must not touch the test head.
Shock absorption tests are more difficult. A blunt object hits the head protection (on a test head) with a given energy. Different shapes of blunt object are used according to the likely hazard e.g. a kerbstone shape is used in some motorcycle helmet standards. For standards where a falling object is the main hazard, the object falls onto the head protection. For standards where the wearer falling over is the main hazard the head protection plus test head falls on the object. Either way, a limit needs to be set on the force/acceleration transmitted to the test head when the helmet is worn: this limit is intended to correspond to an acceptable level of injury. Setting this limit which is difficult, and requires the standards writers to use existing medical knowledge and experience of how head protection performs in use. At the moment, limits on the linear force or acceleration transmitted to the test head are used for shock absorption performance.
What is an “acceptable” level of injury?
This depends on what the injury would be without head protection.
Head protection standards have an introduction including words like “the protection given by a helmet depends on the circumstances of the accident and wearing a helmet cannot always prevent death or long-term disability.”
This emphasizes again that head protection does not offer 100% protection. And, for head protection just as for other PPE, increasing the level of protection means heavier and bulkier equipment which may make working difficult and introduce its own hazards such as thermal discomfort or musculo-skeletal problems.
Construction accidents
A brick drops from the second floor and hits a worker wearing an industrial safety helmet. If the brick weighs 1 kg and drops 5 m before impact then it has an energy of roughly 50 J. The helmet standard uses a 50 J impact for shock absorption, so the helmet should protect the worker from no worse than concussion and bruising - the intended acceptable injury. Replace the brick with a pallet of 50 bricks dropping from the same height. The impact energy is now about 2500 J.
This is well above the energy used to test for shock absorption, so the helmet is no longer in its tested performance zone. The helmet will reduce the severity of the impact and the level of injury, but by an uncertain amount. If a 2500 J impact lasts 0.1 s then the force is roughly 5000 N. Without a helmet this is enough to fracture the skull causing severe injury or death. Even with the helmet this is likely to be a major injury, maybe still fatal.
This is why you should create exclusion areas where there is heavy lifting overhead - head protection is not designed to protect against very heavy falling objects.
SOURCE:
https://www.hsimagazine.com/article/protect-your-head-496
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