Interesting Juan. You are correct in the source of the chart. I had intended to drag the notation as well, but missed it, and was too lazy (!) to go back and get it. I hope Gregg can pop in and explain the inconsistancy.

I will venture a guess as to the white bars, and again, I hope Gregg will give us the real scoop. I think they refer to best case, and then a "loose" case setting, as the products are web and adjustment based.

I think that the HANS is particualrly tempting to wear loose, especially in a sedan, as greater mobility is needed, for visibility, and it's performance drops in such a case.

I think good mirrors are a prerequisit with any H&N system.

Definitely the HANS tether lengths are important. I was very careful to ensure that the lengths were set up to spec.

Regarding mirrors, I was originally concerned about being able to turn my head enough to see out the passenger mirror. In fact my setup allows me to look into the side mirror and also look out of the window reasonably. However, what I found after racing is that the center mirror is much more effective than the passenger mirror, and I end up not using the side mirror at all. It helps that I have a big 14" curved mirror -- it's nice for videos too! I'm thinking of going even bigger with the 17" mirror. You can never have too much rear visibility.

-Juan

Vaughn,

Thanks for posting your notes about that lecture by Tom Gideon, which I cross posted to this site. I have a few comments about some of your followup:

Engineers with partial knowledge scare me. I should know, I'm an engineer and physicist.

I bet the engineer in you thought that Petty bar was a good idea when you put it in, right? Makes the cage more rigid, and that's got to be good, right? Turns out to be a bad idea once you peel a layer off the proverbial onion and consider the dangers of a tube near your head, and also egress issues. The one thing I've learned about race car safety is that there are a lot of layers to the onion. Maybe a race car engineer would have known the tradeoffs.

It's seductively easy to make conclusions based on numbers. The pitfall here is that sometimes those numbers don't tell the full story. Marketing guys love this gambit. They convince you that it's all about a benchmark. And then they proceed to quote you figures for that benchmark, which BTW, they selected to be favorable to their product.

Engineers are especially succeptable to this ploy because they are so self confident. They dig into the numbers to make sure they are accurate, but they really should be digging into whether the benchmark is appropriate. Tricked!

Here's an amusing example of this gambit from the Isaac web site itself:

The full link is: http://www.isaacdirect.com/html/OtherPages/HowToBuy.html

This one is so silly that I don't think anyone here would fall it. Who here is going to risk their neck on a device that has actually been measured to be inferior, just to save a few hundred dollars? That's why you will not find many here buying Hutchins devices. I bet a 50 cent bungee cord beats HANS and Isaac by the proposed benchmark!

Truthfully, the big thing that really bugs me about the Isaac marketing presentation is that it is so glossy and shallow. Look for answers on their web site, and all roads lead to that one glossy chart posted by Jake. That's it. Nothing more.

It doesn't help that Isaac cites the source of competitor's data as having "been garnered from SAE publications and other sources believed to be reliable". Why not cite the sources directly? That is high ratio of hype to substance, and it sets off my warning bells. Just like the supposed extrication comparison of Isaac vs. HANS that turns out to be undocumented, when you ask.

Sorry, Gregg. Nothing personal here. Maybe you should hire a new marketing guy.

I think you are missing the point of this slide. The main point was the force measurements presented at the bottom. It says nothing about position measurments. The head motion discussion provides a good way to visualize the why the H&N restraint systems work. This is after all the summary of the data for the lay person. But HANS didn't quote position numbers. They quoted force, exactly what Gregg was telling you to look for.

In any event, the good thing about HANS' glossy page compared to all the others is that it actually states with some detail the conditions of the test and it also cites the source, so you can verify things. For example, you can go back to the source of the HANS data and verify Gregg's claim that the data is flawed, something I intend to do once Gregg tells us about the errata that was verbally presented.

-Juan

BTW, I intend to followup with HANS about their Email. I share your concern about getting out through the window. I don't think they get that point. Like you, I cannot get out of my car through the window with the HANS on. No problem getting out through the door with device attached, though.

I don't know what to make of Gregg's assertion that the SAE paper which is the source for HANS crash test data is flawed and misleading. It would seem that the assertion is unsupported, when you check into it.

I wrote Dr. Melvin, author of the SAE paper, to ask about the verbal errata that Gregg's mentioned. Melvin wrote back explaining in detail what he said at the meeting, and Melvin confirmed that the printed results are accurate. He offers no correction to the results.

Unfortunately, we have been waiting since last week to hear from Gregg on this and other followup questions. Perhaps he can shed some light on the matter. Here is the statement that Gregg made:



Here is the Email from Melvin, which offers no support for Gregg's assertion.



Gregg, are you out there?

-Juan

Later

Thread continued here "Anyone using the HANS device part 2":

http://forums.pelicanparts.com/porsche-autocross-track-racing/158799-anyone-using-hans-device-part-2-a.html

In General
Much information has been presented on this thread since I visited here last, so it is probably a good idea to step back for a moment and put everything in perspective.

I normally avoid Internet discussions that spiral downward to ever-lower levels of irrelevant minutiae as, frankly, having spent twenty years designing structural implants, I have neither the time nor inclination to revisit remedial biomechanics.

In this thread, however, contributors have offered either personal experience regarding various designs or put forth a significant effort to understand what can be a complicated subject. This rarely happens, and you are all to be congratulated. The least I can do is answer a few questions. Beyond that, you are going to have to do your own homework.

The discussion here seems to fall into two categories: 1) how well various products perform (and how that performance is measured) and 2) who is lying about what. A few miscellaneous questions remain, so I will throw them into the mix also.

Let’s do the ugly part first, i.e. who is lying about what
No one is lying about anything. As has been mentioned, it is very tempting for marketing personnel to grab snippets of evidence favorable to their product and present them as part of a sales effort. For the sake of simplicity, let’s break this down into three product groups: the Isaac system, the HANS device and everybody else. In the “everybody else” group, most manufacturers offer up some sort of claim to the effect that their product substantially/significantly/materially/massively reduces head loads, without getting into the specific level of performance; sort of a binary "It works" approach. Such claims are generally correct in that even the worst performing products used incorrectly will reduce head loads by about 50%. This is a fact (see discussion below).

Insofar as the Isaac system is concerned, we have made no claims in our publications beyond a statement to the effect that no other product has ever outperformed an Isaac system in a laboratory crash test. This is a fact (see discussion below). We did not expect the Isaac system to perform as well as it did but, hey, what can we say? It’s not our fault—Newton was a pretty smart guy.

Insofar as the HANS device is concerned, Hubbard/Downing, Inc. is, in my opinion, making a huge marketing mistake by putting at risk its credibility. The Isaac system and the HANS device are both very good products—clearly superior to others—yet Hubbard/Downing, Inc. attempts to present its product as the only one that really works. This is laughably false, and any racer who does a little research discovers as much.

Further, the HANS Web site compares the product to a limited number of devices--making a point to avoid Isaac test data--and cites performance levels for competing devices that are absurdly low. This is a fact (see discussion below).

When an objective observer weeds through all the product claims and compares them to actual product performance they conclude 1) there is no such thing as a bad H&N restraint and 2) there are only two high-performance H&N restraint products--the Isaac and the HANS.

The HANS device is a good product. If you own one, don't get defensive, just don't believe it is the only car on the track.

Let's get on with the science
It's best to do this in two parts: the physiological mechanism of the injury, and how well various products act to reduce fatal head loads.

(Note: Most of the research cited I have not read in years, so please allow for some memory margin.)

The #1 cause of fatalities among drivers is Basilar Skull Fracture (BSF), which accounts for approximately half the deaths. The balance of fatalities are attributed to less frequent events such as loss of blood, internal injuries, fire, etc. BSF is a broad diagnosis and occurs when the body stops but the head keeps moving. The net result of this dynamic is that the head accelerates away from the body, thereby inducing kinetic energy into the head relative to the body. In order for everything to come to rest, this KE must be reduced to zero. Absent a H&N restraint, the only thing available to absorb this energy is the neck. Given that the musculoskeletal structure at the lower neck is much stronger than at the upper neck, it is the upper neck load which is critical in evaluating any H&N restraint.

The weak link in the chain is the base of the skull--hence the phrase "basilar skull fracture." BSF can take many forms depending on the load vectors/tensors and the build of the driver, e.g. an NFL linebacker has a different build than does Aunt Matilda, and they will probably experience different failure modes at BSF injury limits. Also, the load vectors/tensors may dictate whether the BSF consists of fractures of the foramen magnum, the occipital condyles or some other bony structure.

The body in general and the head in particular experience multiple linear and rotational loads in a crash, all of which are recorded during a crash test. It is generally acknowledged that, insofar as BSF is concerned, the most important load is the "F-sub-z" load. As the scope of SAE paper #2002-01-3306 was limited to BSF, only Fz values were reported although all other measures were recorded.

You may wonder why the fracture of a bone--any bone--could cause death. Good question. Death is actually caused by critical soft tissue injury which occurs secondary to the fracture, i.e. any energy in excess of that required to invoke the fracture must be absorbed by the soft tissue. Such injuries include the severing of the spinal cord, which disconnects the heart from the brain.

Now let's talk about testing.
There are many crash sleds. Some are designed for automobiles, some for trucks, some for trains and some for aircraft. The sled on which more motorsports testing has been conducted than any other sled in the world is probably the 50G decelerating sled at the Wayne State University Bioengineering Center in Detroit. If you invent a head and neck restraint, this is where you test it. It is, to my knowledge, the only sled which has crash tested every H&N restraint you can buy going back over about fifteen years. It is the single best repository of comparative performance testing of H&N restraints.

While referred to as the "50G" sled, the actual peak crash pulse ranges between 45Gs and 50Gs. For Isaac testing, the impacts were between 46Gs and 48Gs, IIRC. We refer to it as a "45G" test in an effort to be conservative, lest someone accuse us of marketing hype. Some details are here: http://www.isaacdirect.com/html/OtherPages/CrashTesting.html

All test results reported on the bar chart on the Isaac Web site use exactly the same WSU test protocol: same crash sled, same crash pulse, same crash dummy, same seat angle, same data acquisition system, same everything. The only difference is the H&N restraint product. Period.

Let's review the chart.

http://www.isaacdirect.com/html/chart.html

which comes from here: http://www.isaacdirect.com/html/chart.html

(Note: 1 Newton of force = 0.2248 pounds of force.)

Going left to right, here is where the numbers come from:

1) None (No H&N restraint): From established baseline testing.

2) Webbing: Testing of the Hutchens, D-Cel and Wright devices as published in various papers or personally witnessed by me. As noted in the first paragraph below the chart, performance will vary depending on how tightly these products are worn--said variation being depicted by the light-colored portion of the chart.

3) G-Force: Company publications.

4) HANS: SAE paper 2002-01-3304 and known variance. When tested with loose straps the HANS device will generate higher head loads, potentially as high as twice the "tight" head loads. This is a note to users to leave the straps alone.

5) Isaac: SAE paper 2002-01-3306 adjusted for upper-neck load cell error.

As Dr. Melvin noted in his e-mail to Juan, with a faulty load cell the HANS device was registering about 1500N. With this same faulty load cell the Isaac system was registering about 1300N, so it was 10-15% better than the HANS device. We were not aware of this error when the 3306 paper was written. Dr. Melvin agreed at the SAE conference that the Isaac values should be adjusted down proportional to the HANS adjustment. When you do the math and convert to English units, the Isaac system was just under 190#. We rounded off to 200# and added 10% to get the HANS value.

(Continued below)

Some loose ends
>Can you tell us what was the verbal erratum that Dr. Melvin gave with the presentation of his paper. I would like to understand that fully when I look at the papers.

I recall Dr. Melvin announcing in his errata that the performance of the Hutchens and D-Cel products were understated in the 3304 paper . In reviewing Fig. 6 of the paper one sees the correct maximum Fz load of 4000N. There is, however, no mention of the improved performance by these products when properly tightened--Fz values of about 2500N have been observed, IIRC.

>Adams writes about Isaac: "The thought of metal rods anywhere near your head or neck scares us, as we have seen a head and neck restraint with such a piece spear the helmet off of the crash test dummy on an impact rebound."

Then the HANS salesman must be really scared of fractured CF near the carotid artery. Dr. Trammel mentioned HANS fractures when he presented his paper (SAE paper #2002-01-3350).

>When asked about the benefits of the Isaac shock absorbers compared to the HANS, Adams states: "There is enough compliance in the human body, as well as the shoulder harness to bring the head to stop gradually, every time. The tethers functioned well even in the 100G sled test…" Do you Agree?

No. And neither does this guy:

"I started to wear a HANS device in 5/94 when it was a novelty item, and it was very comfortable in the car. But, after an incident with a 1600 at IRP in turn 4 the same year, I think I would have rather risked a broken neck over the 'chained' restraint of my head in the heavy impact. The effects have been long lasting, and life altering. If they want to make their product SAFE, there should be a damper in the tethers to decelerate your melon to avoid the injury you will have to live with. Any frontal crash worthy of justifying the cost of the device will leave you something to remember (or maybe not) after your head comes to a profound halt at the end of the rigid nylon straps."

Jon Horgas (Posted 2 Dec 2003 at http://www.apexspeed.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=000188)

Logic dictates that brain slosh will occur when your head yanks at the end of the rope. Jon (above) appears to still be suffering from it ten years later, the HANS salesman says Don't Worry Be Happy and we are accused of marketing hype. Amazing.

Here is what it feels like to hit something while using an Isaac system (see second entry): http://www.isaacdirect.com/html/OtherPages/RacersComments.html

>Also, at what G's will the shock absorbers begin to fail?

About 200.

>The full link is: http://www.isaacdirect.com/html/Oth...s/HowToBuy.html

>This one is so silly that I don't think anyone here would fall it. Who here is going to risk their neck on a device that has actually been measured to be inferior, just to save a few hundred dollars? That's why you will not find many here buying Hutchins devices.

I agree, but we are in the minority: The HANS device is not the #1 selling H&N restraint in the U.S. Beyond that, a HANS buyer actually pays a premium for a product that does not perform as well as an Isaac system, so one can see there is little logic in the purchase decision.

>I bet a 50 cent bungee cord beats HANS and Isaac by the proposed benchmark!

So what? Water costs less per gallon than gasoline. Does that mean you should put it in your tank? Water won't run your engine and a bungee cord won't save your neck. Any measure of value compares cost to performance.

>Truthfully, the big thing that really bugs me about the Isaac marketing presentation is that it is so glossy and shallow. Look for answers on their web site, and all roads lead to that one glossy chart posted by Jake. That's it. Nothing more.

That's correct. That's it because there is nothing more. The only crash lab where every product has been tested is at WSU. When another series of tests is conducted, we will make every effort to include that science on our Web site. To our knowledge, the chart is the only scientific summary of relative product performance for nearly every product available. If you want a good example of a company's Web site that compares its product only to inferior designs, go elsewhere.

Summary
Those are the basics. If you want to drill deeper into this subject, begin by reviewing the publications that support the 3304 and 3306 papers. If you continue back through the research trail you will eventually arrive at studies conducted for the U.S. Air Force that include the sacrificial crashing of live Rhesus monkeys. One of our neurosurgical clients assisted in this testing.

Gregg, Thank you for your detailed reply to some of the questions raised in this thread. We are indeed trying to make sense of a lot of information, some conflicting, about the performance of the various devices, so your help is greatly appreciated. Also SAE 2002-01-3306 leaves unexplained data needed to understand the the measurements reported for Isaac. I have a few followup questions, as I am not clear on some of your points.

Can you clarify the conditions for the sled pulse used for the Isaac measurement in 3306: was the pulse the same as used for the 3304 paper for the other devices? The 3304 pulse modeled a 35mph velocity change with a peak decerlation of 50G using a square pulse shape, i.e. approximately constant 50G deceleration for 30ms. 3304 explains the test conditions and provides a graph. Same graph, same parameters for Isaac?

Regarding the errata that you describe:

Are you are saying that Melvin stated that the Hutchens and D-Cel devices were not properly adjusted in the test? If so, did Melvin give a figure for how much the results were understated?

Regarding the 2500N Fz value that you quote for Hutchens/D-Cel, where are you getting that number from?

Regarding your chart comparing the performance of ISAAC to HANS and other devices, I have still not been able to reconcile the numbers on that chart against any of the published data in 2002-01-3304, 2002-01-3306, or elsewhere. For example, the figure for HANS is not as given by Melvin, as he gives a value of 868N (195lbs) for HANS, while your chart seems to indicate a value greater than 200lbs. Also, the baseline value in your chart appears to be 1800lbs, while Melvin measures 1147lbs. Can you give references to where we might find the values that you used in the Isaac chart?

Regarding the overall performance of ISAAC, do you have Isaac data for the same parameters that Melvin measured for HANS, Huchens, and D-cell, i.e. Fx, Mx, My, neck extension, photos? If so, can you provide a report on that data? And can you provide some pictures of Isaac in action showing position and extension of the head during the crash that you measured. Since this important data is available for the other devices, it is important that it be presented for Isaac as well.

Thanks for the followup!

-Juan

Juan,

Read my posts again. All but two of your questions have been answered there.

Gregg, Perhaps I misunderstood your posts. Perhaps you weren't clear in all respects. I am asking follwup questions because I needed further understanding than what I could glean from your posts. In any event you say that there are some questions that are unanswered anyway. Answers to the followup questions would be appreciated.

-Juan

Juan,

The only questions you have which were not addressed in my previous posts are, in effect:

1) Melvin's errata.

Answer: Melvin acknowledged that the Hutchens and D-CEL devices are more effective when worn tightly.

2) Source data for naked dummy and "tight" webbing.

Answer: The same source as for all the data--the WSU lab. The webbing data has been published somewhere, and the baseline data has been around forever.

Now that this has been thoroughly explained, I have a question for you: Do you acknowledge that the Isaac system performs just as well as the HANS device, if not better (ignoring the "getting barbequed" part)?

Gregg, Before I answer your question, I would like to ask you if there anything more data that you can share with us about Isaac? The data in 2002-01-3306 is minimal (one data set, one crash type, only Fz, data set contains errors), and there are huge gaps between what is published there and what is published for other products. It only makes sense to answer your question based on the full information about Isaac.

I am about to leave for a race weekend, so I won't be able to respond until I return next week.

-Juan

Sorry, Juan. It's has taken too long to get up to speed on Fz only. I don't have time for the other 32 variables.

There is no scientific evidence that Isaac is safe, let alone better
than HANS, Hutchens, or D-Cel devices. Simply put, Isaac is an
untested prototype that is not ready for human use.

Let's review. The data for Isaac is published in SAE 2002-01-3306 [9]
and consists only of neck tension measurments, Fz, for a single data
set, and a single test configuration. That prototype's parameters
were tuned to the specific test conditions to get a good benchmark
value for Fz. Further, the Fz value that Isaac promotes is better
than the published value in SAE 2002-01-3306. Greg says that the
published data contained errors, and needed adjustment. Other important
measurements like Fx, Mx, My, head extension, HIC, head accelerations,
and photos are not available. We have asked for other test reports,
and Gregg has said there is nothing more.

By contrast HANS, D-Cel, and Hutchens, as well as baseline conditions
have been studied by Melvin and others using thourough scientific
methods, which included multiple measurements, elimination of
systematic errors, and comparison against control data [8].
Measurements of Fz, Fx, Mx, My, head extension, HIC, head
acceleration, and photos were reported and evaluated against injury
thresholds, or accounted for in terms of measurement limitations.
This data was presented in SAE 2002-01-3304 [8]. The results for HANS
and baseline were compared against results measured in completely
different study [7], and found to be in agreement.

The performance of the HANS Device has been extensively studied since
1990 by Melvin and others. See attached reading list. This study has
included testing of 0, 30, 36, 90, and 180 degree impact angles [3, 5,
7, 8], in addition to examining HANS device sensitivity to impact
pulse shape, strap tightness, and neck length. Real accidents have
been studied, and the outcomes with and without HANS have been
compared to evaluate safety and effectiveness [6]. Mechanical
degredation of the HANS device after impact has also been studied [6].
After 14 years of study and use, reports about HANS are favorable,
and HANS is strongly recommended by Melvin [10] and others.

Basic research and testing has not been done for Isaac to deterimine
its safety and effectiveness. There is more to evaluating neck
restraint than just Fz. Without sensitivity analysis and testing, it
is unknown how much Fz and other measures may exceed injury thresholds
under real conditions like impact angles, body types, and usage.

The race car driver should not take lightly the dangers of any device
that limits helmet movement. Without scientific test results, it is
impossible to know whether the Isaac prototype works and is safe.
Isaac users are unknowingly putting themselves at great risk by using
this virtually untested device.

-Juan


Reading list:

[1] Hubbard, R., and P. Begeman, "Biomechanical Performance of a New
Head and Neck Support", presented at and in the Proceedings of the
1990 Stapp Car Crash Conference, Society of Automotive Engineers, SAE
Publication P-236, 1990.

[2] Hubbard, R., P. Begeman, and J. Downing, "Biomechanical Evaluation
and Driver Experience with the Head and Neck Support", presented at
and in the Proceedings of the Motor Sports Engineering Conference and
Exposition, Society of Automotive Engineers, December, 1994, SAE paper
no. 92466, 1994.

[3] Gramling, H., Hodgman, P., and Hubbard, R., "Development of the
HANS® Head and Neck Support for Formula One", 1998 Motor Sports
Engineering Conference Proceedings , Society of Automotive Engineers,
December 1998, SAE 983060

[4] Melvin, J.W., Baron, K.J., Little, W.C. Gideon, T.W. and Pierce,
J., "Biomechanical Analysis of Indy Race Car Crashes", Proceedings of
the 42nd Stapp Car Crash Conference . Society of Automotive Engineers,
November 1998, pp. 247-266, SAE 983161.

[5] Gramling, H. and R. Hubbard, "Sensitivity Analysis of the HANS
Head and Neck Support", presented at and in the Proceedings of the
Motor Sports Engineering Conference and Exposition, Society of
Automotive Engineers, November 2000, SAE paper no. 2000-01-3541, 2000.

[6] Terry R. Trammell and Robert P. Hubbard, "Medical and Technical
Outcomes of HANS® Use in CART", SAE 2002-01-3350.

[7] Gideon, T.W., Streetz, L.M., Willhite, S., and Melvin, J.W., "ATD
Neck Tension Comparison for Various Sled Pulses", 2002 Motor Sports
Engineering Conference Proceedings , Society of Automotive Engineers,
December 2002, Paper No. 2002-01-3324

[8] John W. Melvin, Paul C. Begeman, and Craig D. Foster "Sled Test
Evaluation of Racecar Head/Neck Restraints", SAE 2002-01-3304

[9] Gregg Baker, "The Use of Dashpots in the Prevention of Basilar
Skull Fractures", SAE 2002-01-3306

[10] Rocky Entriken, "Heads Up" SCCA Sports Car Magazine March 2004.

[11] FIA Standard 8858-2002 HANS System

[12] FIA List of FIA approved HANS Devices according to FIA Standard
8858-2002 and Compatible Helmets.

[13] Robert Hopper, James McElhaney, and Barry Myers, "Mandibular and
Basilar Skull Fracture Tolerance", SAE 942213

Juan,

That's pretty funny. I doubt any of the authors of the papers you reference would agree with you.

Lighten up, Juan.

Although I think more testing of any device is always a good thing. I have to say, we might be looking at an Engineering 'fixation spiral' here. ;)

Wow.



Rocky will be thrilled to see his name next to such luminaries, not to mention being cited as an expert!

And if the Isaac is unfit for human use, what about the S & M devices?

(Can't argue with the conclusion that more data would be nice, and I too would like to see a matrix chart of all products at all test values, but time waits for no man)

Just doing my home work. I'd rather be accused of being fixated, than being a (crash test) dummy. ;)

Seriously Jack, don't take my word for it. Read Greg's report on Isaac (SAE 2002-01-3306) and Melvin's on HANS, Hutchens, and D-Cell (SAE 2002-01-3304.) Then let's see what you have to say about Isaac.

-Juan