HELMET DROP!!
Ultimate HDF Member
Joined: Apr 2006
Posts: 5,230
Likes: 4
From: Amherst, VA
RE: HELMET DROP!!
I use my helmet like "Xena Warrior Princess" I wip that puppy off my head and wing at cars turing in front of me and on the sides, knocking them back into reality. Then I throw it back on my over inflated head and ride on!
Now according to the experts I am not allowed to do this. Shoot
[align=left] [/align]
Now according to the experts I am not allowed to do this. Shoot
[align=left] [/align]
RE: HELMET DROP!!
Helmets are meant to crush on impact and absorb the shock instead of your head doing the absorbing. As one who has also been involved with racing, (Drags, motocross, trials and Baja) I can assure you the 3 foot fall can destroy a helmet's ability to properly do its job. Whether or not any individual wants to gamble that their helmet survived such a drop is strictly up to that person.
The science is what it is in any case.
The science is what it is in any case.
Banned
Joined: Mar 2007
Posts: 857
Likes: 2
From:
RE: HELMET DROP!!
ORIGINAL: lawhd
I disagree with their logic & hypothesis.
Given:
The mass of a body determines the momentum P of the body at given velocity v; it is a proportionality factor in the formula:
P = mv
The factor m is referred to as inertial mass.
But mass as related to 'inertia' of a body can be defined also by the formula:
F = ma
By this formula, the greater its mass, the less a body accelerates under given force. Masses m defined by the formula (1) and (2) are equal because the formula (2) is a consequence of the formula (1) if mass does not depend on time and speed. Thus, "mass is the quantitative or numerical measure of bodyâs inertia, that is of its resistance to being accelerated".
Assume:
1) The mass and density are the greatest for the shell. (they better be, or it's REALLY gonna hurt if you fall)
2) The shell impacts first
3) The impact is not perpendicular, but tangential...even minimally
4) The impact is not felt as a single point, but some force is displaced rotationally (curve of helmet)
5) There is no "head" or any other object in the helmet)
6)This is important...no stress or micro fractures occur to the outer shell (since Snell does not mention this, I will assume it to be true for the given proof.)
Given and assuming these parameters, it does not take a mathmatical wizard to see that the contents of the shell (i.e., the foam cushion layers) "see" very little of the impact of an empty helmet stricking the ground.
Well...THAT was OBVIOUS!!!
ORIGINAL: mark1957222
From the Snell website:
"Helmets are normally comprised of four elements; a rigid outer shell, a crushable liner, chin straps or a retaining system and fit or comfort padding. The rigid outer shell when present adds a load-spreading capability, and prevents objects from penetrating the helmet. It's kind of like an additional skull. The liner, usually made of EPS (expanded polystyrene) or similar types of materials absorbs the energy of an impact by crushing. The chin strap when properly buckled and adjusted along with the fit padding helps the helmet remain in position during a crash. Helmets work kind of like a brake or shock absorber. During a fall or crash a head is traveling at a certain speed. Since the head has weight, and is moving there is a certain amount of energy associated with the moving head. When the helmet along with the accompanying head impact an unyielding object; a rock, a wall, a curb or the ground the hard shell starts by taking the energy generated by the falling helmet (head) and spreads it over a larger portion of the helmet, specifically the internal foam liner. The foam liner then starts to crush and break which uses up a lot of the energy, keeping it from reaching the head inside. Depending on how fast the head is traveling, and how big, heavy and immovable the object is the faster the head slows down, and the more energy is present. In short everything slows down really quickly. A helmet will effectively reduce the speed of the head by breaking and crushing which reduces the amount of energy transferred to the brain. The whole process take only milliseconds to turn a potentially lethal blow into a survivable one."
Because of the different layers involved in how a helmet reduces the impact of an accident, coupled with the fact that the part that absorbs most of the impact is not even visible, a drop of anything higher than 1 - 2 feet onto a hard surface can, effectively, render a helmet useless as protection in an accident - even if there is no visible damage. [/align]
From the Snell website:
"Helmets are normally comprised of four elements; a rigid outer shell, a crushable liner, chin straps or a retaining system and fit or comfort padding. The rigid outer shell when present adds a load-spreading capability, and prevents objects from penetrating the helmet. It's kind of like an additional skull. The liner, usually made of EPS (expanded polystyrene) or similar types of materials absorbs the energy of an impact by crushing. The chin strap when properly buckled and adjusted along with the fit padding helps the helmet remain in position during a crash. Helmets work kind of like a brake or shock absorber. During a fall or crash a head is traveling at a certain speed. Since the head has weight, and is moving there is a certain amount of energy associated with the moving head. When the helmet along with the accompanying head impact an unyielding object; a rock, a wall, a curb or the ground the hard shell starts by taking the energy generated by the falling helmet (head) and spreads it over a larger portion of the helmet, specifically the internal foam liner. The foam liner then starts to crush and break which uses up a lot of the energy, keeping it from reaching the head inside. Depending on how fast the head is traveling, and how big, heavy and immovable the object is the faster the head slows down, and the more energy is present. In short everything slows down really quickly. A helmet will effectively reduce the speed of the head by breaking and crushing which reduces the amount of energy transferred to the brain. The whole process take only milliseconds to turn a potentially lethal blow into a survivable one."
Because of the different layers involved in how a helmet reduces the impact of an accident, coupled with the fact that the part that absorbs most of the impact is not even visible, a drop of anything higher than 1 - 2 feet onto a hard surface can, effectively, render a helmet useless as protection in an accident - even if there is no visible damage. [/align]
I disagree with their logic & hypothesis.
Given:
The mass of a body determines the momentum P of the body at given velocity v; it is a proportionality factor in the formula:
P = mv
The factor m is referred to as inertial mass.
But mass as related to 'inertia' of a body can be defined also by the formula:
F = ma
By this formula, the greater its mass, the less a body accelerates under given force. Masses m defined by the formula (1) and (2) are equal because the formula (2) is a consequence of the formula (1) if mass does not depend on time and speed. Thus, "mass is the quantitative or numerical measure of bodyâs inertia, that is of its resistance to being accelerated".
Assume:
1) The mass and density are the greatest for the shell. (they better be, or it's REALLY gonna hurt if you fall)
2) The shell impacts first
3) The impact is not perpendicular, but tangential...even minimally
4) The impact is not felt as a single point, but some force is displaced rotationally (curve of helmet)
5) There is no "head" or any other object in the helmet)
6)This is important...no stress or micro fractures occur to the outer shell (since Snell does not mention this, I will assume it to be true for the given proof.)
Given and assuming these parameters, it does not take a mathmatical wizard to see that the contents of the shell (i.e., the foam cushion layers) "see" very little of the impact of an empty helmet stricking the ground.
Well...THAT was OBVIOUS!!!
Are you saying you think a helmet dropped 3 feet is still OK to wear? The drop will cause no damage to the helmet?
Intermediate
Joined: May 2006
Posts: 48
Likes: 0
From:
RE: HELMET DROP!!
If anyone is interested in the real story as to what Snell says, go to their website. They have a frequently asked question section. The following is cut and pasted from the Snell FAQ:
I dropped my helmet! Do I have to go buy a new one?Generally the answer is probably not. Helmets are one use items, but are quite durable otherwise, at least the ones we certify. Frequent dropping or spiking a helmet on the ground, or other hard surfaces may eventually degrade the helmet's performance. Similarly if the helmet falls to the ground at highway speeds unoccupied the owner must be aware that some degradation may have occurred. In general the real damage comes when the helmet contacts an object with a head inside. The Foundation recommends that if you are participating in an activity that requires that you wear a helmet, that you avoid hitting stuff with your head. It can be difficult to readily determine if a helmet has been damaged, and the protective capabilities compromised without a thorough inspection by a trained professional. Some manufacturers may provide this service or direct you to these others that can perform these inspections. The Foundation recommends that if you suspect your helmet may be compromised, then replace it. If the helmet has been involved in an impact while in use, replace it.
I dropped my helmet! Do I have to go buy a new one?Generally the answer is probably not. Helmets are one use items, but are quite durable otherwise, at least the ones we certify. Frequent dropping or spiking a helmet on the ground, or other hard surfaces may eventually degrade the helmet's performance. Similarly if the helmet falls to the ground at highway speeds unoccupied the owner must be aware that some degradation may have occurred. In general the real damage comes when the helmet contacts an object with a head inside. The Foundation recommends that if you are participating in an activity that requires that you wear a helmet, that you avoid hitting stuff with your head. It can be difficult to readily determine if a helmet has been damaged, and the protective capabilities compromised without a thorough inspection by a trained professional. Some manufacturers may provide this service or direct you to these others that can perform these inspections. The Foundation recommends that if you suspect your helmet may be compromised, then replace it. If the helmet has been involved in an impact while in use, replace it.
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