DJF1

FBB, there are a lot of questions that are not answered. While the physics do make sense, looking at both websites for product comparison, besides the data displayed there are plenty of pictures which demonstrate clearly the function of HANS in an accident and these pictures are backed up by all these Pro organizations who have approved and some mandated ( like F1) the use of the specific devise!!!
Yes I do understand about policies, politics, money etc... but the fact remains that there are a lot of unaswered questions about the Isaac. On the HANS the straps are mounted on the special collar. On the Isaac they are mounted on the seatbelts and there is a "roller" I looked and looked at the site and I still have yet to understand if the seatbelt mount is a moving part or not and how this will react in the accident. While an even force frontal impact would most likely be a simple thing for the Isaac, your head is anot always straight and the impacts are not always straight. Since the mounts are on the seat belts and we all know how the seat belts stretch in an accident what will be the effects of the Isaac in relation to that and in relation to the position of your head?
I DONT want to flame the Isaac, I'm just provoking a conversation in hopes that there will be a more extensive analysis and explanations about this product.

Bill Gregory

Basic ISAACS is $725 vs $865 for the 20 degree HAN fiberglass model. Different models and options can raise the price on both.

It shows the HANS device provides alot of protection, and that both Hutchens devices, Hutchens device and D Cel (believe the Simpson harness is based on one of them) also provide protection, although allowing closer to the injury level. The article can be downloaded from the SAE website for $12.

Noticed on the Hutchens website that they have a new safety device (R3)that looks like a HANS-style device that you wear, which isn't dependant on a harness setup to work.

Hadn't thought about it....the Hutchens site they say their device is not recommended for open face helmets...makes sense.

924RACR

Greg, I'd like to hear more, in detail, about what you feel (or know) to be the approving side for those sanctioning bodies. Please more than just hints - you may have legitimate points, but we need more detail.

Danny, to answer some of your questions as best as I can - yes, the seatbelt mount part of the ISAAC moves forward rolling on the belt as needed on impact. This compensates for belt stretch. Your point about oblique angles of impact is very good - that's one reason I chose the ISAAC over the HANS, actually. The HANS is designed explicitly for the longitudinal impact. Of course, so is the ISAAC - however, the ISAAC has more additional benefit in an oblique or lateral impact than the HANS. That's my own opinion, I should clarify, by inspection of the design and by my own personal impact test. FWIW, I am a mechanical engineer and work in vehicle safety systems (admittedly, chassis controls, not restraints).

So my assessment is, in our type of racing the worst case impact would be spin and stop on track, then get t-boned by another car - not sliding up into a concrete barrier without even a gravel trap. So I'm most concerned about a lateral impact, not head-first into a wall at speed. Additionally, you have to look at the design of the cars we're driving. In a formula type car, the nature of the cockpit is such that there's much lateral support for the driver; if they go in sideways, the entire body hits the side of the cockpit evenly at the same time, in a nicely controlled decel. In our cars, there's nothing on the right side to stop you other than a) your seat (only stops your torso, or maybe not even that depending on seat design and mounting), and b) any additional braces you have added. Maybe you spent the big bucks and have a good seat with shoulder and head braces. Then on the left side, you hit the door or bars and the window net.

So, IMO, this is the area which requires the most attention in our cars, not just from the point of head restraint choice. But, since this is the topic at hand, I felt that the dual shock design of the ISAAC would be more likely to offer benefit in a lateral impact than the HANS (recalling that the HANS uses straps which much be fully extended before doing anything, and cannot work in compression). This series of conclusions was, for me, sufficiently answered when I put my car sideways into the armco last Aug. I had the ISAAC, and it did its thing. I didn't have any additional side bolsters for myself (just the seat, a Kirkey circle track seat), and I went sideways far enough (impact was on the RH side of the car, and backwards) to hit my petty bar. My biggest mistake in setting up the car was not getting around to adding those additional side bolsters I'd planned. Fortunately, I survived no issue in spite of that.

Greg Fishman

Vaughan,

I have a nice video on my harddrive, and will try to find someone who has the website for it, from a press conference that NASCAR did on head and neck restraints.
They showed test from the HANS, Hutchens, and no device and compared them. The HANS was by far the best alternative.

SCCA PRO required the use of approved Head and Neck restraints several years ago. Here is a link from their BBS. http://bbs.sccaproracing.com/ubb/For...ML/001637.html It is a long drawn out thread but there is some info in there about the testing procedures SCCA did to determine which devices were approved. Anyone's device could be submitted and be an approved system if it passes their tests.

I am not an engineer so I sure can't speak to whether the Isaac device is good, bad or otherwise. But for me, the HANS is a much better device due to its proven ability in real world accidents and in tests. A IRL driver survived a 130g force collision this year, car was crushed to the footwell and he walked away without even any soreness. There are numerous other examples as well.

I am sure there are lots of politics that go on in racing at all levels but I am not cynical enough to believe that politics are involved when it comes to safety equipment and protecting drivers.


Photo of actual tests:
http://www.autoracing1.com/images/20.../hansdev5a.jpg

article from which that photo came from. http://www.autoracing1.com/GoodBoys/001107HANS2.htm

gbaker

Gentlemen,

I'm an engineer with Isaac, LLC.

Some interesting points are being raised here, and they seem to fall into two categories: the performance of the Isaac system, and the policies of various sanctioning bodies regarding head and neck restraint products in general. Let's do it in that order...

First, nothing has ever outperformed an Isaac system in a laboratory crash test. Nothing.

Forget photographs and videos. Injuries are caused by loads to your head, not the position of your head. You can prove this yourself. Tilt your head as far as possible. Guess what? You're not dead.

If you aren't sure how an Isaac system works, that's okay. It's our job to make it work. Personally, I'm not sure how a light bulb works, but I don't use kerosene lamps. The simple explanation is that the Isaac system absorbs shocks to the head by using shock absorbers. Shocks work based on velocity, not position, and function in compression as well as in tension. Other head and neck restraints place your head on the end of a rope, and do not function until you reach the end of the rope.

All references in this thread to comparative test data are to those developed before the invention of the Isaac system and exclude Isaac test data. If you wish to review Isaac test data, see the peer-reviewed SAE publication #2002-01-3306. If one combines these test data with those presented in SAE publication #2002-01-3304, and includes test data from other manufacturers, one has the comparative performance chart we present on our Web site--same crash lab, crash sled, crash dummy and crash protocol.

There is nothing wrong with buying a position-based head and neck restraint that was invented in the last millennium. It will work, but that's like buying a kerosene lamp, which also works.

Don't get me wrong. If you are driving around with a naked head, please get a head and neck restraint, even if it's not ours. Half of racing fatalities are due to head and neck injuries and there is no such thing as a bad head and neck restraint. Some are just better than others.

Second, of the hundreds of racing clubs in the world only two, for all practical purposes, exclude the Isaac system from their list of approved products: NASCAR and FIA. Nearly all the other bodies mentioned in this thread are either affiliated with these two or follow their lead regarding safety. After recent driver fatalities, NASCAR upgraded its safety program and considers current products adequate in minimizing head and neck injuries. After Bobby Labonte had to remove his HANS device this past summer to exit a burning Winston Cup car, I expect NASCAR will eventually expand its list of approved products.

FIA refuses to test any new products, even after the HANS device put F1 driver Justin Wilson in the hospital last year after the belts slipped off. They consider the HANS device to be adequate and have told us this in face-to-face meetings. Our understanding is that FIA (or its affiliates) has the exclusive distribution rights for the HANS device within FIA sanctioned races, so for them to test any other design means they would be testing a competing product.

The vast majority of sanctioning bodies (there are approximately 400 racing clubs in the U.S. alone) either allow the use of the Isaac system or include it in their list of mandated head and neck restraints, including SCCA Pro Racing, Trans-Am, the Vintage Auto Racing Association, various circle track clubs, etc.

DJF1

Gregg, thank you for your explanation. I was hoping you can jump in on this... Can you please explain the bit about the rollers and the belt mounting. Having seen how the belts stretch I'm not quite sure what are the mechanics behind the belt mounts. On the HANS its pretty simple to figure out how it works as the mount moves with you so the length and position of both straps pretty much remain to a certain angle so your head does remain within a certain angle from your body and neck. With your mounts I'm not sure how they stay in place in relation to the head and neck position.

TIA

gbaker

The rollers allow the belt connection to move forward with the body on impact. The belt connection is positioned at the back of the shoulders, while the shocks extend and hold your head on your neck. In this regard, it is similar to the HANS device in that everything stays with the body during a crash. The difference is that shocks don’t wait for your head to reach a certain position, they begin to function the instant the head starts to accelerate away from the body. Shocks don't care about position, only velocity.

It is obvious how a Hutchens, HANS, D-Cel, White, Wright, etc. work. They, to one degree or another, hold the head back. The shorter and more rigid they are, the better they work. That's why the HANS works best of this group: the straps are short, and the composite structure is rigid.

I will admit that it is not obvious how an Isaac system works. You need to think about it for a while. It is a mechanism that reacts only to velocity, the kind that occurs when your body stops and your head keeps moving. If you get it, fine. If you don't, crawl under your car, look at the suspension, and ask yourself, "Why do I need shocks if I have springs?"

Keep in mind that the idea is to limit the load on the head, not the position of the head. One can limit the loads by limiting the position--and all position-based head restraints do this--but why bother? The #1 complaint drivers have about these products is their limitation of head mobility. We could limit head position by using shorter and stiffer shocks, or using multiple shocks connected to shoulder components, but performance gains would be minimal and the system would become much more complex.

fatbillybob

You know, just as an aside, if you look at your anatomy books the Splenius Capitus muscle is your god given Isaac. It is a design that makes sence for your body.

gbaker

FBB,

Good point. The loads attempt to pull your head off the top of your neck, and the Splenius Capitus muscles do a pretty good job keeping everything together, along with the bone structure, up to about 900 pounds. Rather impressive when you think about it.

The trouble is, a 50G hit will generate a load of about 1,800 pounds, so the SC muscles need some help.

smokey

I'm trying to decide between a HANS and an ISAAC (just DE, but big head, skinny neck, age challenged, 25 track days per year), and I have one question: what stops the forward motion of the roller on the belt with the ISAAC? Does it get pinched between the belt and the shoulder? It's very clear how the HANS works: it applies a force roughly perpendicular to the neck to stop the forward motion of the head. The force applied by the ISAAC is at a more acute angle, and if it's parallel to the neck on impact, it would allow the neck to elongate as it absorbs the shock - which may be fine if it reduces the load. It would deal with the axial load, but not the radial shear load. I haven't read the SAE papers, and perhaps it's explained there. Anyway, I apologize for being pedantic, but I'm a mechanical engineer, and I'm reluctant to use a life-critical device whose operating principle I don't understand - light bulbs notwithstanding. How does the ISAAC work? More specifically, at impact, how do the ends of the ISAAC device move as the shock absorber elongates? Does the roller stop by being pinched between the belt and the shoulder, then providing a pivot point for the shock absorber (and the helmet)? Or what?

gbaker

Smokey,

Good points all. Whenever I answer questions on a forum I’m never sure who the audience is, so I tend to tone down the technical side. Since you’re a gearhead like me, let’s go over the belt connector, body/head motion and load measurements in more detail. Then I’ll get into how the Isaac system works.

(Hey, it's lunch and I’m bored. If I get a chance I’ll post today.)

Yes, the belt connector ends up pinched between the belt and the shoulder. Both ends of the dampers are equipped with spherical rod ends, so the range of motion is the same whether the driver moves their head relatively slowly or a crash causes rapid motion. The difference, of course, is that any rapid motion invokes a damper reaction.

You raise an interesting point regarding the overall geometry. The dampers are more vertical than horizontal on initial impact, especially if you have an integral headrest with your seat. As the body loads the belts it moves away from the seat—probably 8 to 10 inches in a 45G impact. Due to the inherent friction of the belt connectors, they tend to lag the body motion slightly and adopt a more horizontal orientation, then rapidly “catch up” to the body and lodge at the junction of the shoulder and the belt.

The vertical component of the initial damper reaction causes a slight compression, followed by tension at the end of the event. BTW, all products—and a naked head—will cause both compression and tension, for a variety of reasons. Also, loads listed on our Web site chart are absolute values.

The dummy measures 33 different variables, including shear. Data is collected at rates ranging from 1,000 to 10,000 samples per second. At the neck-head junction, all six loads of interest are measured, i.e. linear and rotational loads about the X, Y and Z axes. The most important is the linear load along the long axis of the neck, F-sub-Z. Shear and rotational loads for the Isaac system are not at the injury levels. Hubbard/Downing, Inc. has, to our knowledge, never published these values for the HANS device, but I suspect they are similar.

Before I get into the details of how the Isaac system works, it is important to review the physics.

Basilar skull fractures are caused by excessive F-sub-Z loads, which are generated in a two-step process. First, the body stops and the head keeps moving, so the head is accelerating away from the body at an increasing rate (the plot of acceleration vs. time is shaped like an inverted “V”). Then the head must decelerate to a stop, and this is where the problem begins. We know from Newton’s Second Law of Motion the force needed to decelerate a mass: F=ma. With a naked head, the only “F” is F-sub-Z. The mass is fixed, so the force is determined by the peak velocity and how much time/distance is available for deceleration to V=0. Unfortunately, the unprotected driver runs out of time and the head loads spike to about 1,800 pounds in 30-50ms. 900 pounds is lights out, fade to black.

Any head and neck restraint puts another “F” in the equation: its reaction. The F-sub-Z load to the head will be the total load (F=ma) less the restraint reaction, or:

Fz = ma – Fr

Classic, position-based designs attempt to hold the head back, which generates the restraint reaction, so:

Fz = ma – dE

where d = displacement and E = elasticity of the system.

This reaction, however, does not occur until it becomes tight. Until then, the head is gaining velocity at a very rapid rate. A HANS device works better than a webbing product like the Hutchens/Simpson because there is little stretch in it, so the reaction occurs sooner, the velocity is lower, and the head load is lower. If you increase the length of the HANS tethers, head loads will increase.

So how does an Isaac system work? The same basic equation applies (Fz = ma – Fr), but the restraint reaction term is different:

Fz = ma – CV

where C = damping coefficient and V = velocity.

(Given that velocity is the first derivative of position, and that acceleration is the second derivative of position with respect to time, the solution is a second order, first-degree differential equation.)

Two very interesting things happen when you take out the tethers and replace them with dampers: 1) The faster the head moves, the greater the damper reaction and 2) the damper reaction begins the moment the head starts to move. Both of these characteristics work to minimize head velocity and loads, without regard to position.

Forget force for a moment and look at this from the perspective of kinetic energy. In order to stop a moving head one must dissipate its KE. Since KE is a function of the square of velocity (KE = 0.5mv^2), which is increasing at an increasing rate, it is critical to invoke the restraint reaction at the earliest possible moment in order to minimize KE.

Obviously, I’ve simplified some of this and didn’t mean to get so wordy here, but there is no easy way to verbalize a complex crash that is best understood by reviewing load cell data.

So much for theory. What happens in the real world? In sequence, here’s what occurs when a driver using an Isaac system hits something:

1) Car crashes.

2) Seat begins to stop.

3) Body moves forward while decelerating, head keeps going, dampers begin to react and become more horizontal (all at about the same time).

4) Dampers reach maximum extension while rolling forward to the belt-shoulder junction.

5) Isaac system becomes an extremely rigid head restraint.

In other words, the dampers react very early to minimize the KE, and then everything locks up as the dampers reach maximum extension.

We are all going to have to trust the crash dummy on the numbers, but you can try an Isaac system with our rental program. Borrow a HANS and decide which you prefer.

smokey

Gregg, thanks for the explanation. It makes sense. The main problem is the axial load, and the ISAAC starts to take the load in an axial direction once the roller is jammed between the belt and the shoulder. As you say, the main principle seems to be to assist the SC muscle in the tension stage of the "cracking the whip" scenario. I understand now, so I just have to decide. I appreciate your offer, but the car is hibernating till April.

DJF1

Yeah, it does make sence and thanks for the explanation... One final question on my behalf...Is there any chance the roller jumping your shoulder? Wouldn't kind of a conneting strap between the two rollers be a safeguard that one roller does not jump the shoulder if that is at all a scenario to happen?

gbaker

Smokey,

You're welcome. Get back to us in April.



Danny,

We had some thoughts about this also until we saw the belt loads, which total 8,000-10,000#.

The load on each belt is about 4X the load on each ISAAC belt connector, so the connector can't squeeze forward beyond the shoulder.

fatbillybob

Intersting point Gbaker and Danny, but Gbaker can't the connector roll forward of the shoulder in a violent sub-crack the whip accident that ends up to be a crack the whip accident? An example might be a rolling car where the connector could get pinched forward due to the unpredictable action of the body in the car and then slam nose into a wall for the final head whipping accident? It seems like a tether between connectors going behind your neck would be a good thing?