New Bonehead - shrunk a bit due to low temp?

[vonSanta 0]

Just got a new Bonehead Mindwarp, 2002 model. Put it in the oven as per instructions and "molded" it around my head. Fit great afterwards.

So I went for the X-mas jump yesterday. Around -2C on the ground, maybe a little colder.

The helmet seemed to have shrunk! Couldn't get my head to the top - if I pushed it down, it'd go back up. Felt like it was a size smaller. Sister said it was my fault somehow, but she's a cheeky bastard.

Anyway, I come home, helmet acquires room temperature - and a perfect fit again!

Is this because it's new, because I made some error "baking" it or is it just the material (carbon fiber?)?

Santa Von GrossenArsch
I only come in one flavour
ohwaitthatcanbemisunderst

[Hooknswoop 19]

I don't think it would shrink with cold. It may not flex as much and may be harder to compress the foam padding. I have found that a helmet's fit is affected a lot by how long it has been since your last haircut. Is your hair langth longer than when you molded it?

Derek

[miller 0]

Were you trying to put it on at altitude or on the ground?

Bonehead's "thermofit" liners definitely expand at altitude. Ask anyone who is breaking in a new flat-top pro. I've actually heard at least one person who put their helmet on on the ground and left it on for the entire ride to altitude because they couldn't get it on at altitude.

If it was on the ground, and it didn't fit, I might agree that the foam just stiffened up due to the cold, or maybe your head grew?

Mike

[vonSanta 0]

HooknSwoop: Same hair length. Molded it the day before yesterday, jumped it the day after. It fit like a glove when I tried it on the same morning.

Miller: hm, you're probably right. I wore it from the ground up (to keep my ears warm out in the cold
Maybe my head grew? What, you in liason with my sister? She said that my head (and ego) grows with the more jumps I get. You're both evil creatures.

I'll stick with the foam padding stiffening due to cold.

Thanks

Santa Von GrossenArsch
I only come in one flavour
ohwaitthatcanbemisunderst

[sducoach 0]

The first few times (20-30) wear it to altitude. Bonehead used to rec. this. I don't know if they still do. The foam will take a better "set". When new the foam will expand at altitude enough to seem tight.

Blues,

J.E.

James 4:8

[linestretch 0]

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Bonehead's "thermofit" liners definitely expand at altitude.

just to add a little bit to this. I know of 2 jumpers that lost their boneheads (one with a camera, one without) and they both said that it always seem to fit very snug at altitude, but under canopy, it was always really loose. Both were lost in freefall.

my pics & stuff!

[sducoach 0]

I jump a Flat-Top Pro and an Optik. I've had them "snug up" at altitude but never become loose at ground/canopy ride level. That sounds more like a miss-fit on the forming.

Hook hit one thing on the head that may play into your experience, hair. When this old man lets his hair grow out the fit requires an extra notch or two. If the form was set with a lot of hair and then the hair was cut short I could see a problem with "loose".

Edit,

The Optik chin strap does sometimes work a notch or two loser. Even after their strap design change. Were both Optiks?

Blues,

J.E.

James 4:8

[linestretch 0]

yes, both were optiks. The guy who lost the camera was pretty experienced, not a slacker. The other was a gal that was pretty new.

my pics & stuff!

[MichaelBess 0]

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Maybe my head grew? What, you in liason with my sister? She said that my head (and ego) grows with the more jumps I get. You're both evil creatures.

You are not far off. When you are at altitude your head actually does expand slightly. If you have a very tight fitting helmet on the ground, it will be tighter at altitude every time. I am not sure how temperature affects size as much as altitude. The video helmets I manufacture have a chin latch mechanism that I have to make sure to leave a bit of extra room to allow for expansion. Otherwise it will not latch at altitude.

You could try re-fitting your helmet while wearing a very thin hat. Something like a T-shirt thin firesuit mask. Make sure there are no seams in your hat. It really wont take much, just remember if it ends up too loose you run the risk of losing it in freefall.

Just a few thoughts...

[DrAvalanche 0]

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You are not far off. When you are at altitude your head actually does expand slightly.

I find that very hard to believe. The skull is a fairly rigid structure that doesn't expand unless you crack it (witch really can't be recommended), or are a little baby. That leaves only the soft tissue and that would be very little unless you hammer it into something hard and get a bump of course .

I'll stick with the theory that my brothers head is expanding due to an over-dimensioned ego!

"We Are The Light At The End Of Your Sorry Little Tunnel"

[MichaelBess 0]

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I find that very hard to believe.

I can appreciate you questioning what may appear to be hard to believe. I suggest you study a bit. Maybe look at the following links as well:
http://www.britishairways.com/travel/healthbody/public/en_
or:
http://www.flyana.com/dvt.html

There are many more articles and studies but these were the first few that came up when I did a google search "body expands at altitude"

Pretty cool huh!

[DrAvalanche 0]

Well. It doesn't say that the head expands. It say that air trapped inside cavities in the head (i.e sinuses, middle ear etc.) expands. Since the bony cavities of the skull doesn't expand along with the air, this may cause pain due to increased pressure, BUT the volume of the head will not expand.
So I stand by my statement. The head doesn't expand in altitude!

"We Are The Light At The End Of Your Sorry Little Tunnel"

[MichaelBess 0]

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Since the bony cavities of the skull doesn't expand along with the air, this may cause pain due to increased pressure, BUT the volume of the head will not expand.

It's OK, A bunch of folks decided to stick by the story that the earth was flat once too

Neither of the links I posted state "the skull doesn't expand" (in such an eloquent misuse of the English language) so I'm not sure where you got your information. The head does indeed get bigger at thinner altitudes and I stand by my statements.

The head is inclusive of skin, muscle tissue, hair, 14 facial bones, 22 skull bones, ligaments, etc, etc.

Cool link showing how all the bones go together:
http://face-and-emotion.com/dataface/physiognomy/cranium.jsp

This is an excerpt from the first link:

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"This is because the thin, high-altitude air causes our bodies to balloon out something like the Michelin Tire Man."

This is an excerpt from the second link:

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"When the body expands, the blood automatically flows more slowly. Picture a river. The water runs swiftly when it flows in a narrow channel, but when the river widens, the water moves more slowly and may also pool in some spots."

Looks like we agree to disagree and it will have to be a good debate for someone else to research and set us both straight...

Is there a Dr. in the house?

[vonSanta 0]

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Is there a Dr. in the house?

Dude, you're in for it now

Santa Von GrossenArsch
I only come in one flavour
ohwaitthatcanbemisunderst

[DrAvalanche 0]

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It's OK, A bunch of folks decided to stick by the story that the earth was flat once too

Yeah, but those guys where religious .
I am a smegging doctor!
And I don't claim that any of the articles say "the head doesn't expand". I claim that the skull doesn't expand. The links you posted are about DVT and gas expansion due to the decreased pressure at altitude. This is completely unrelated to your claim that the head expands at altitude. And as for free gas in the blood the cause the expansion I can inform you that most gases in the blood is chemically bound to the forming elements of the blood (e.g hemoglobin) for example 95% of oxygen is bound to hemoglobin, only 5% is physically resolved in the blood. Because of this there will be very little expansion of bloodgas during climb to altitude. It's a totally different matter if we're talking scubadiving where nitrogen is dissolved in the blood. and tissue. this gas will cause expansion during uncontrolled assent. But again that is a totally different matter.
What I'm saying, and now it's your turn to study the articles a little closer, is that nothing in the article supports your claim that the head expands at altitude.
I've spent 7 years in med school looking at pretty pictures like the one link you sent. So I'm not just sticking with some dumb ass idea I found somewhere in space.
And If you look at the pretty picture you will see that the bones of the skull is tightly fixed to each other. Thereby the skull case doesn't expand. As for the soft tissue it consist manly of water and dry substances. And water is a fluid and thereby non-compressible that is a fluid doesn't expand in altitude the same goes for the soft tissues. One of the article reffered to DVT (deep venous thrombosis). this occurs manly in the veins of the leg and pelvis. this causes stagnation of blood in the venous system which may give rise to oedema, that is water in the interstitiel tissue, and a swollen limb. But again this doesn't affect the veins of the head, and doesn't cause the volume of the head to expand. If there indeed is any expansion of the soft tissues of the head during climb this would indeed be very minimal.
And don't believe anything you read in a article on the net... the net is full of B.S
Feel free to correct me, I haven't researched the subject. What I have written is what I know from my education and knowledge of physiology. But if you do, please add some science and a plausible (and relevant) medical explanation to why the head expands at altitude.

"We Are The Light At The End Of Your Sorry Little Tunnel"

[linestretch 0]

I gotta agree with the "I don't think so" philosophy too. I'm with the Dr.

my pics & stuff!

[DrAvalanche 0]

Thank you!

"We Are The Light At The End Of Your Sorry Little Tunnel"

[MichaelBess 0]

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If there indeed is any expansion of the soft tissues of the head during climb this would indeed be very minimal.

Then we both agree that the head does increase slightly at altitude. Thank you!

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And don't believe anything you read in a article on the net... the net is full of B.S

I could not agree more.

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Feel free to correct me, I haven't researched the subject. What I have written is what I know from my education and knowledge of physiology. But if you do, please add some science and a plausible (and relevant) medical explanation to why the head expands at altitude.

I was asking others WITH medical explanations to assist us in our debate as I am not a Dr. nor do I study medicine.

I have no claim to the medical profession (other than basic CPR, first aid, and first responder training) so I can not make any medical claims as to the “Why”. If you are looking for a medical explanation stop reading now, and have a nice day.

If however you will count years of observation and a scientific study I did about this specific topic, read on.

Are you claiming to be a Dr.? Have you studied this effect as I have over time and with personal observations in varying conditions? I did ask for more than a med student to help us address this issue... I am not discounting your 7 years of study in the medical field and at the same time I would request that you do not discount my 13 years of study on this topic.

I'm certain there have been a plethora of studies in hyperbaric chambers by many of our planets military physicians and scientists regarding this or similar studies. I would love to see if there have indeed been any sanctioned studies (not opinions) as to the amount of size increases to various parts of our bodies including the head. I never claimed that the skull bones increase in size, although I would find it very hard to believe that they do not increase slightly. Yes they are tightly woven together as one unit but even solid steel increases and decreases in size. Remember that ANY increase in size "IS" an increase even if I have to get my machinist calipers out to measure that increase.

As I stated all along! The HEAD (inclusive of more than the "Skull alone") does expand slightly! I have more video jumps (by more than 4 times) than you have total jumps. That alone states very little with one major exception. My video helmets are custom made by myself to fit very tightly, as did the first person's helmet (Claus’s) in this post. I have personal experiences that above 10,000 my helmet fits noticeably tighter than it did on the ground EVERY time regardless of temperature variance. By temperature variance I mean the difference in temperature at ground level and exit altitude (eg. 60 deg. F ground temperature and 38 deg. F at altitude would equal a 22 deg F variance). I am not the first person the notice this phenomena. This leads me to believe one of three possibilities. 1) The helmet shrinks, 2) the head expands. Or 3) A combination of the two.

I will attest that temperature plays a part in almost everything shrinking and expanding so we need to eliminate temperature from the study to determine if 2 is plausible. We do that by looking at total temperature variance versus size change using altitude variance (eg. a 20 degree temperature variance versus a 50 degree variance using the same altitude variance). Since my study did reflect this then we need to look at altitude causing the helmet to shrink. I have no reason to believe this possibility because of my experiences as a machinist so I simply discount it as plausible.

Since the helmet fits the same (tighter at altitude) regardless of temperature changes (between the ground and at altitude, eg. a 50 degree variance versus a 20 degree variance at the same altitude variance) and is made from very stable materials (fiberglass and hard Styrofoam), we can eliminate temperature from the study. If temperature was the factor it would be dependent on the variance of the temperature and increase or decrease based on the variance.

My deduction is quite simple that the head does indeed expand slightly at altitude enough as to affect the fit of the tight helmet I describe. This is proven fact.

I stand by my statements. I know the increase in size is slight, and only affects a very tight fitting stable (no open cell foam liners etc.) helmets. I will however do a personal study and try to measure the effects as well as I can with a measuring instrument. This debate has piqued my curiosity as to the total increase in size.

Feel free to study this yourself by making a casting of someone's head as I have. Then try and get it on them at altitude. Then try again on a day with less temperature variance between the ground and at altitude. You will have to deduct what I did if the casting was tight to begin with and the person did not change their hair length or style.

[vonSanta 0]

I was asking others WITH medical explanations to assist us in our debate as I am not a Dr. nor do I study medicine.

Semantically speaking, you asked for a doc. The person you're discussing this with is just that. Sorta cool, no?
Are you claiming to be a Dr.?

She's stating that she is one (in fact, I think she's at work right now). I can PM the phone number to ya if ya want to (we live in Denmark, so it might be an expensive call though).

Remember that ANY increase in size "IS" an increase even if I have to get my machinist calipers out to measure that increase.

Semantically you'd be right. In terms of the discussions it's irrelevant; the increase must be large enough to affect the fitting of the helmet on my head.

As I stated all along!
Aw c'mon! This is stretching (pun intended) it a bit. A microscopic change isn't applicable for this example. But, i'll give it to you that semantically, you're right

This leads me to believe one of three possibilities. 1) The helmet shrinks, 2) the head expands. Or 3) A combination of the two.

Can we add 3) "the lining stiffens and compresses less or similar thing"? If so, we're in complete agreement.

I will attest that temperature plays a part in almost everything shrinking and expanding so we need to eliminate temperature from the study to determine if 2 is plausible.

We'd have to eliminate all bogus variables and isolate the one we're examining. Then we'd need a control group. We'd need reliable, objective ways of measuring. The experiment needs to be reproductable(sp?). Only then are we somewhat close to a scientific experiment.

In other words, we need to take the equipment out of the question and go with the head alone. It is quite interesting, this - do you have any suggestions on how we can accurately measure the head? Could be cool to do an experiment.

Since my study did reflect this then we need to look at altitude causing the helmet to shrink.

Coolness, you did a study? Got a link so I can check it out?

I have no reason to believe this possibility because of my experiences as a machinist so I simply discount it as plausible.

Aye, experience does count. however, for it to be a scientific experiment we need to disprove or prove things. For instance, it might be that the lining has small air pockets in it. The gas within them expands, making for a tighter fit. Or some totally unexpected thing cause the same thing - we won't know til we've done some experiments.

My deduction is quite simple that the head does indeed expand slightly at altitude enough as to affect the fit of the tight helmet I describe. This is proven fact.

I wouldn't call it a scientific fact, it's a deduction or a good guesstimate based on years of experience. I think for it to be a fact in the scientific sense, we need more empirical data and tests.

We can agree that something is happening. Your years of experience says one thing; my years of experience carrying a head on my shoulder says another.

As I said, the helmet didn't fit properly on the ground - in other words, we can take altitude out of the equation. Your study suggests we can take temperature out of the question too. So, although this is far from a controlled experiment, what do we have left?

I stand by my statements. I know the increase in size is slight, and only affects a very tight fitting stable (no open cell foam liners etc.) helmets.

I agree - this *is* an interesting discussion. My helmet is fitted with a liner though, so I guess we'd have to take that into consideration too?

I will however do a personal study and try to measure the effects as well as I can with a measuring instrument. This debate has piqued my curiosity as to the total increase in size.

Neat! Any idea on how you're gonna measure the helmet? I mean, it's a curved thing that's hard to measure accurately. I ask because I want to do some experimenting too.

Feel free to study this yourself by making a casting of someone's head as I have. Then try and get it on them at altitude. Then try again on a day with less temperature variance between the ground and at altitude.

Ah, that's one way. Messy though - must get a haircut first.

Isn't there a possibility that there are qualities in the casting that makes it susceptible to shrinking/expanding? I.e that it is not clear whether it's the head expanding or casting shrinking? We'd need to study the material in question. Shouldn't be too hard.

Santa Von GrossenArsch
I only come in one flavour
ohwaitthatcanbemisunderst

[Jonsmann 0]

I think the size changes of your helmet is from thermal expansion (contraction when it gets colder). Most things get larger when heated and smaller when cooled. This applies to your helmet too. Simple thermal contraction can account for maximum 0.5 mm in diameter change. However, when I look at my bonehead it is made up of 2 layers, the fiber closest to the head and the lacquer at the outside. If there is a difference in thermal expansion coefficient between the two layers, temperature variations could make the entire helmet flex in unpredictable ways (it is a shell, and therefore hard to predict). Do a search on "thermal bimorph", for more info on this effect.

No changes in the size of your head. Bone, water and tissue are considered incompressible, and certainly will be for the 0.4 bar pressure change to 4000 m. The head is at a constant temperature so no thermal expansion (or contraction there).
The only thing that could change the outer size of the head, is expansion of the air in the middle ear. For most skydivers this should not be a problem as we generally have a permanent open eustachian tube. If you have a very narrow tube, or just had a cold it could be a possible explanation (but I don't think so).

- Jacques

[MichaelBess 0]

Semantically speaking, you asked for a doc. The person you're discussing this with is just that. Sorta cool, no?

She never stated she was a Dr. only that she had studied medicine for 7 years. I asked if she was a Dr. and still ask that question for my own curiosity. Cool if she is and could help with the medical side of a series of new tests.

Semantically you'd be right. In terms of the discussions it's irrelevant; the increase must be large enough to affect the fitting of the helmet on my head.

Close. On my head because it was my study that I did. It was done because it did indeed affect the fit of my helmet. I found it really did not take much to fix it in the form of making the lining bigger. Maybe a T-shirt thickness (plus a touch) around the circumference of the top of my head did the trick. This is why I suggested that particular thickness to repair your problem with fit. I encourage anyone to perform as creative a test or series of tests that they like and share their findings.

Can we add 3) "the lining stiffens and compresses less or similar thing"? If so, we're in complete agreement

Yes you can for your study if you call it 4). 3) is still valid. It would be necessary if there were any foam in the equation.

For mine it became irrelevant because my helmet has very little pliable foam lining. My lining is rigid Styrofoam as I stated and the only compression would be a very thin fabric covering the Styrofoam. It is under full compression at the ground and at altitude so not a factor. If a helmet were to have any closed cell foam within the liner I would assume it may make a difference. Maybe the trapped air in the closed cells? Worth looking into.

Neat! Any idea on how you're gonna measure the helmet? I mean, it's a curved thing that's hard to measure accurately. I ask because I want to do some experimenting too

I completely agree it's a hard thing to measure accurately without compression of the soft tissues etc. I was thinking of using a mold that I made from plaster. A VERY messy job by the way. It's a complete head mold including the jaw line. If I put tooling points into the plaster (a series of bushings) and fit the mold on the ground lining up a jig that would accurately measure and hold the mold together on those points with pins. Then repeat the process at altitude using a controlled set of temperature variables I hope to do jus that. The measurement would be the increase of gap where the mold is cut into two to allow it to go on your head. If it will not go on due to expansion "side to side" then I would have to devise a 4 piece tool (by cutting the mold front to back) and measure across all points. Would make for a neat test and the measurement would be relevant.

Isn't there a possibility that there are qualities in the casting that makes it susceptible to shrinking/expanding? I.e that it is not clear whether it's the head expanding or casting shrinking?

Yup, that was my reason for listing 3) as plausible. I have to figure that something very thick (like the Plaster mold) has a very rigid property and with any study we have to make certain assumptions.

Coolness, you did a study? Got a link so I can check it out?

Nope, the closest I have to posting my findings are the past few days ramblings here. I do not have a web site yet.

By the way, the reason I got into measuring in the first place is that I make video helmets and had to figure out how tight I could make them. The tighter the fit the less your skin is allowed to move on your skull causing camera shake. When doing video work you want the helmet to become a part of your body. I stumbled on to the expansion thing when I made a few too tight. They would not latch at altitude without serious discomfort. Get on the ground and it fit again. I had to figure out why so I started doing tests.

[Amazon 7]

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Maybe my head grew? What, you in liason with my sister? She said that my head (and ego) grows with the more jumps I get. You're both evil creatures.

PSSST.. I theenk I have to agree mit der sister

Its the swollen head thing for shure duuuuude

Oh and we know I am the Evil Jeanne

Oh by the way.. I gt to jump my HAVOK finally tomorrow in Eloy... neenere neener.. bet it would be too cold there....

[vonSanta 0]

Aaaah, the good ole evil jeanne is back!

And I'm the first to get to know. How 'sweet' of ya

Santa Von GrossenArsch
I only come in one flavour
ohwaitthatcanbemisunderst

[DrAvalanche 0]

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Are you claiming to be a Dr.?

If you deside to trash me, please do me the curtesey an read what I written.
I personaly think that "I am a smegging doctor" is a quite clear statement, but hey what do I know.
So here it is loud and clear. Yes I am a doctor!. Well that wasn't very objectiv, but I needed to get it out of my system. Now I'm all nice again.
And yes I still would like to get a medical expalantion or indead theory to your claim for the sake of my curiosity, so if anyone has it please speak up. I would very much like to know what kind of study you've been doing on the subject, how it was built, for what purpose and what the result was.
I have no doubt what so ever that you are far superior to me in any and all areas of skydiving. I'm not writing this to diss you or piss you of...(well mayby the first couple of lines in this post...), but simply because I disagree with you.

And for anyone who is curious my nickname has nothing what so ever to do with my profession. It's the name of the drum-machine of my favorite band The Sisters Of Mercy

"We Are The Light At The End Of Your Sorry Little Tunnel"

[DrAvalanche 0]

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The only thing that could change the outer size of the head, is expansion of the air in the middle ear.

Well,this isn't true. Increased pressure in the middle ear will not cause any change to the outer size of the head.If the pressure is to high the ear-drum will burst, air will escape and the preassure will reduce.

"We Are The Light At The End Of Your Sorry Little Tunnel"