ltc

Please ignore duplication with ColorChange.
Apparently I was typing as he was typing and didn't see his post until after I submitted my reply.
Damn, I hate wasting John D's disk space

SundayDriver

Tim,

I see you are back to your charm school responses.

In your first section, you make a case for the dashpots doing a better job. My point is that no safety EXPERT has said this is better. Neither you nor I qualify as a safety EXPERT. I am still waiting for such person to speak up.

I really enjoyed your response to my QUESTIONS in the second section. How the f&*^ can I be WRONG when I made no assertion there. I only asked questions. So Tim, do you have videos of both frontal crashes and side crashes with the ISAAC. I am not as dumb as you like to imply. I know the theory of the ISAAC. What I have never seen is video that shows just how far forward the ISAAC shoulder belt parts move forward in a crash.

If you think that because no one has succesfully sued the maker of a safety device that it is effective, then I am amazed at your position. I guess that means that every product that has lost a product liability suit in the last year was actually safe before the legal action. Come on - lack of legal action to date, does not make something safe. Ask the couple of guys who suffered major injury to femoral arteries about the safety of some devices that have not lost a legal battle yet.

SundayDriver

OK. I am alive but that is no where close to what happens in a big crash. So, Lewis, do me a favor. Consider, but don't do the same experiment. Then with your shoulders and body restrained, have someone pull your head downwards and forward another 12". That is much closer to a crash scenario.
Now I never implied that ISAAC would not restrain the head, as does the HANS. I also agree that the idea of a dashpot would seem to make it better. But not all safety things work as you or I might think they should. I am simply asking if and safety EXPERTS have shown the dashpot idea to add any value.

I don't understand your push a string concept. The HANS has two straps. When the head is moved sideways, one of the straps will go in tension. While not the primary value of H&N, I can attest (firsthand) that the HANS does have some positive effects in a side impact.

924RACR

The mechanism of basal skull fracture is one of tensile force loading on the spine, not displacement or velocity. The dampers, being a velocity-dependant function, will seek to minimize the acceleration, thereby minimizing the F in the previosuly-cited equation. That said, testing has shown both the HANS and ISAAC to be effective at the same level of load reduction on the sled. Even the hated Hutchens et al strap devices have been tested and shown effective (better than baseline - unrestrained) on the sled (when properly adjusted, as with the HANS).

Every cornerworker I've heard from says they have NO concerns about getting a driver out in the event of an event - that's what those wicked knives they carry are for.

SundayDriver

Just so it isn't lost, I am going to repeat what I think is a very significant question about the ISAAC.

Is it possible for the parts that ride on the shoulder belts to rotate on the belt and create a dumping situation? As far as I am aware, there has been only limited sled testing of ISAAC and there is not that much real world experience with it either.
Anyone prepeared to answer that question with FACTS, rather than speculation and empty arguments?
I don't know the answer to this but would certainly be interested in the answer.

ColorChange

Mark:

No offense intended, simply direct and accurate communication. In my second comment, I should have said your concerns are wrong or based upon wrong assumptions/understanding. My mistake and I apologize.

Here are some more facts and data for you.



For additional information on how various systems perform, check the SAE web site at http://www.sae.org. Extensive comparative testing was conducted during the summer of 2002, the results of which were presented at the SAE's Motor Sports Engineering Conference in December 2002 and are available as an SAE technical paper (Paper Number 2002-01-3304). Also available is the SAE technical paper titled "The Use of Dashpots in the Prevention of Basilar Skull Fractures" (Paper Number 2002-01-3306), which describes the development of the Isaac® head and neck system. These papers can be downloaded from the SAE web site for a modest copyright charge.

While I agree that blindly assuming a product is safe because of our legal system is insane, I know some of the people at ISAAC as a result of my purchasing investigation and have read their papers. The people involved are credible, and I think the product is sound, although neither of us are biomechanical crash test engineers.

Just for the record, what is a dumping situation?

ltc, you must be an engineer.

SundayDriver

I have seen that chart and, in fact, purchased almost all the SAE papers on H&N devices. The conclusions have generally been that certain devices do a good job of controlling the head in an impact. None have been identified as being significantly better than the 'pack' which includes the HANS. Any tests that have shown better performance (paraphrasing) have not been so much better to fall outside repeatability range. Now as I recall (and I could be wrong) the extensive comparitive testing did not include the ISAAC. The data you show is collected from multiple tests in different sessions, though pretty much all are from the same facility.

Belt dumping occurs when an adjustment buckle is twisted sideways and the belt is scrunched to one side. There is a strong belief that this happened in Dale E's fatal crash and led to belt webbing failure. It is a well documented problem and a huge risk. Typical scenario is that the adjustment buckle that is at the bottom (two slots, not the one you use to tighten the belts) hits the seat during a crash and it is twised sideways. The belt dumps and fails. Anything the surrounds the belt could very likely lead to dumping if it is twisted in a crash. Since the ISAAC involves a part that surrounds the belt, that seems like a risk to me.

ltc

Agreed. I obviously oversimplified my position in attempt to make a simple point regarding limiting motion to less than is available from normal skeletal construction.
However, I would still contend that given the same 'active length', a dashpot derived system is superior than a standard non active tether' vis a vis deceleration. Sir Isaac's laws are still valid in this case (although I do enjoy Einstein's Laws as well)

My only concern is in the unbiased nature of EXPERTS. Consider the retaining of 'expert witnesses' in certain trial situations (doctors, engineers, etc).
Depending on who is paying the bill, the 'opinion' of the expert will be biased towards that side's argument.
Data interpetation, analysis and summaries are all subject to the same principles.
From my own background in engineering and law (and some exposure to medicine.....remember, I don't really have a life), some principles, concepts are just intuitively obvious and therefore I will tend to agree (or trust/believe) with them.
I have had many 'experts' render an opinion; it is up to me to be comfortable with their opinion before I apply it.

On a slightly darker front, you are forced to consider other non linear (human) factors in the sales, financial, marketing, certification of any device (the world is NOT what we were led to believe as children I'm afraid) and to 'experts' and the design of experiments, data collection and reduction and publishing. I certainly hope that is not the case in H&N or other mission critical safety systems or components, but it must be factored into an analysis.

Again, an oversimplification in an effort to save typing. Given the geometries of the HANS collar to its helmet attachment points connected with non rigid tethers (and their length), the HANS would not be expected to have any orthagonal (90deg) impact performance, not until the tether under tension becomes active (the other tether is useless, as you can't push on a string). In contrast, and not necessarily design intent, a rigid assembly (dashpot) on both sides of a helmet sitting on belts/shoulders will have SOME mechanical rigidity in a orthagonal impact; SOME being a bit more than the HANS, especially given the small amount of velocity control the dashpot would provide when active in this case.
(again, this is sort of 'how many angels can dance on the head of a pin, as neither device was designed for pure orthagonal impact)
Again, I would consider it prudent to assign this task to a secondary H&N restraint component (seat design, netting, etc)

I am relieved that you were not injured and that H&N systems worked.

924RACR

Regarding purchase choices, the two significant factors that pushed me towards the ISAAC instead of the HANS (the only two I was considering at the time) a couple of years ago (pre-SFI 38.1) were: the conceptual superiority of the dampers vs. webbing (though they seem to come out even or close enough to not be statistically significant in actual testing) and the potential for superior performance (still, to date, no experimental data to back this up) in the lateral and/or oblique impact. Secondary factors were price (got a huge deal through improvedtouring.com, nearly at half price) and availability/downtime - HANS's were rather backordered thanks to the recent departure of Dale Sr. and subsequent attention, as well as F1's mandate, not to mention I'd have to send off my helmet (again, at the time) for fitting and potentially miss months of racing vs. order and install the ISAAC myself.

The only of these issues that seems to remain to differentiate is the lateral/oblique performance. As mentioned, I still know of no crash-test data relating to ISAAC's performance in this area. I've done my own testing, the hard way, and survived, but that is anecdotal. I do know that testing with the HANS has shown that it's pretty much not contributing substantial support beyond a fairly narrow impact angle (per Tom Gideon, GM Racing). Again, there's no actual data to support ISAAC performance in the obliques.

Without question what IS needed in the oblique and lateral impacts is inner side nets as seen in NASCAR. Which I now have in my car. But that was handled on another thread.

As for SFI 38.1, it's still a lingering question out there, but needs time to mature and see what direction the winds will take us. It's just, for me, another example of a very frustrating fact of life with safety systems. While we want this stuff available to us YESTERDAY, it can't be made available until it's proven out. In the meantime, we get to know about it, but can't buy it (or can't reasonably afford it)... and just have to suffer knowing that we aren't doing every last thing possible to ensure our own safety until testing is complete, development is complete, and/or the devices are available and affordable.

fatbillybob

So why don't they put Isaacs on the HANS and ditch the HANS tethers? Now I think we have covered all bases. I bet patents are the problem. Don't the HANS tethers stretch so you don't get brain slap really? Also,shocks can lock faster than anything when subject to quick dampneing force so with a big hit doesn't the Isaac just lock like HANS teathers so brain slap is brain slap?

On a related note somewhere I read before the HNR the steering wheel limted head movement. If this happend that has gotta hurt more than the airbag. So why is SCCA looking at Airbag elimination I.e. an issue with airbags hitting the chinbar of full face helmets?

ColorChange

No fatbilly, the ISAAC dramatically reduces the velocity of your head when the hard stop comes. So, much less brain slap. Combining the HANS with dashpots could be good. I don't share the same concerns of the belt issues that Mark does.

Mark: I am not sure the belt dumping applies as where the ISAAC sits is clearly visible and it would be hard to imagine being able to fold the belts to begin with inside the bracket, and then not notice secondly.

Geo

Jumping in late here....

Colorchange, do you have data to support the fact the dampers control deceleration of the head better than the straps? Intuitively one might come to that conclusion, but the reality may be different.

Vaughn, I've seen Gregg say that it's the G force that causes basil skull fracture, but I've already read tsomething by either Dr. Melvin or Dr. Hubbard that displacement causes basil skull fracture. Now, I admit I'm just a monkey trying to keep my head attached, but intuitively (there is that word again - filling in the blanks I suppose) it makes more sense to me that it's displacement. Your spine doesn't explode when subjected to high g-forces does it? If you were strapped rigidly to a board for instance and experienced those g-forces, would you still experience basil skull fracture with no movement of the head, neck, and shoulders?

To all, I just purchased my HANS in November and read when 38.1 came out that H-D was looking into getting retroactive approval for recently sold devices. I received a return e-mail today from the person who sold me my HANS and installed my helmet attachments. For $15 I can send the device back to H-D and receive certification. If you have a device w/o the cert, you should contact Hubbard-Downing.

ltc

George, the answer is both, it's just that one drives the other. Please see below.

No (with an explanation)
Think of it this way (and we'll all avoid the math), using jumping off a building as an analogy.

It's not the fall that kills you, it's the stopping.
Put another way, it's not the acceleration (free fall, 1G) that kills you, its the sudden deceleration, or the sudden change from terminal velocity to zero velocity.

Step off a milk crate and you're fine.
Step off 100 milk crates and land on cement and you're not.
Step off 100 milk crates and land on an airbag (like stuntmen) and you're (probably) fine.

Same principles (thank you Sir Isaac), just different results.

Applied to a H&N (and simplified, assuming the "tethers" keep the head attached to the neck), the longer the distance the body and head is allowed to move thru , which is analagous to the height of a building, the greater the velocity the body/head is allowed to achieve before the "stop".

Now, STOP the body, but keep the head from moving forward, the greater the deceleration force the head will be exposed to when the "tethers" snap tight.

Make the "tethers" shorter but "stretchy", analagous to landing on the airbag, less deceleration (insert calculus, area under the curve, 2nd order equations, yadayada).

Make the "tethers" ZERO length, in your example keeping you strapped to a backboard, the head doesn't move with respect to the body and your whole body gets exposed to the deceleration forces (hard stop or aribag stop).

Prevent the head from getting ahead of the body...
or
Minimize the distance which it's allowed to get out in front (shorter tethers)....
or
Control the velocity and the distance you allow the head to get out in front of the body....

you minimize its gain in velocity and thus you minimize the deceleration forces, which are what 'pull' the head off the spine in BSF.
BSF is also produced by a hangman's lynch (same principles as above). You are simply "pulling the head off the spine" (again, simplified to ignore ligaments, tendons, etc)

I hope I wasn't too confusing and was somewhat helpful.

Sounds like the $15 merely covers the administrative costs/fees associated with SFI recertification.

JackOlsen

I chose the Isaac because it is a simpler, more elegant solution to the problem. It utilizes the harness belts in a way that won't allow them to slip off. It's not susceptible to user 'adjustment' in a way that might compromise safety in order to increase comfort. It doesn't require diligent replacement of the straps on a regular basis.

Also, I worried about trying to climb out a car window with a Hans on.

My non-scientific assessment is that both are adequate products. The Isaac might be the Betamax to the Hans's VHS, in both the good and bad sense of that comparison. Safer money is on the Hans, since they have money and momentum. If they get their way, they'll eventually be the only game in town. But to me, the Isaac seems like a slightly better product.

Now, all of that said? I'm in the dubious position of being on the same side of the fence as ColorChange, which makes me a little nervous.

Still, I'll keep my Isaac.

RedlineMan

I'm not sure of your point in mentioning this, but it may be more salient than you know. Lew, if you have done as much studying as I think you have, you should be familiar with the reason why this is the best position for your skull to be in, and why a single impact is not the ogre under the bed that it is generally thought to be. If you are, then this is for everyone else who does not know.

The forward rotation of the head is a key point in surviveability with ANY H&N device. The forehead is the strongest part of the skull. By using the natural forward rotation of the head (this occurs in almost all impact situations because of bio-mechanics), the strongest part of the skull is utilized by pressing it into the front/top of the helmet bucket to absorb the impact. This is a very advantageous position.

Further, it is my understanding that head injury studies have shown that the brain can actually tolerate fairly extreme loads as long as they are single and linear. I am not an engineer, and I know that there are terms to describe such things, second order equations or some such babble. What is truly injurious to the brain is any force that is not linear, that causes any rotational motion of the head. The whip is the real killer, not the linear impact.

It would seem to me that both the HANS and Isaac do a good job of handling these linear impacts. If the Isaac does indeed reduce the severity of deceleration, or the length of time before it "takes up," then that would seem to be an advantage.

Both of them rely on the safety belts, which to my mind is a bit of a crap shoot. The Isaac would seem to have an edge in being semi-connected to the belts, but if the belts stretched a tremendous amount, would that advantage be essentially nulified?

I like the simplicty of the HANS. Either the strap material will take the load, or it won't. There is not much gray area there. Up until it fails, it is essentially 100% reliable.

I really think the Isaac is a stunning piece of conceptualization and design. However, I have a hard time being completely confident that a mechanical device like a shock absorber will be 100% reliable. I've just seen too many things that were impossible in my time.

Lots of questions. In then end, I agree with the spirit of your statement. Any H&N system (a good one) is better than none at all. Right from the Isaac website!