HANS :head restraint:seminar or presentation report
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Time and again the Formula 1 world has proved that the safest place on earth is inside an F1 car. The number one cause of racing related fatalities was the basilar skull fractures from excessive head motions and neck loading. With the introduction of the new Head And Neck Support (HANS) the drivers were able to overcome the only window for injury.
The fundamental purpose of the system is to effectively form a single Ëœbodyâ„¢ of the head and torso. HANS is intended to prevent driverâ„¢s head from being thrown forward in an accident, a situation which could lead to an overextension of the spinal column.
Only recently has the racing industry acknowledged that the number one cause of racing-related fatalities is basilar skull fractures from excessive head motions and neck loading. Racing legend Dale Earnhardtâ„¢s death proved to the racing world and the general public that what appears to be a low impact crash can be fatal. Under development and extensively tested for over a decade, there is a device that can reduce the risk of serious injury or even death to the driver in such a crash. It is the Head And Neck Support (HANS) device.
The HANS, head and neck support was invented by Dr. Robert Hubbard, a biomechanical engineering Professor at Michigan State University. Many debilitating or fatal head and neck injuries could be prevented using this system. The original HANS is shown in Figure 1
In 2000, compact versions of HANS (Figure 2) were developed for CART, IRL, F1, NASCAR, NHRA, ASA, Sports cars, Power Boating and many other racing series.
Extensive testing has proven that HANS consistently reduces the injury potential from head motions and neck loads.
HANSÂ¦.UP FOR SAFETY
The latest example of the engineersâ„¢ efforts to make Grand Prix racing as safe as possible is the new Head And Neck Support (HANS). The system is easy to use and extremely effective. It prevents over-extension of the driverâ„¢s neck region in the event of extreme deceleration. It is designed to Ëœcompleteâ„¢ driver head protection, covering the one aspect to be still exposed.
Forward movement of the head and neck has, until now, been the only unrestrained area in driver impact safety. Extensive research and testing has resulted in what experts now believe to be a practical solution to the issue.
HANS features a carbon fibre collar connected securely to the upper body, with straps attaching it to the helmet. The four main parts of the system are:
1. Support brace- rests on shoulders.
2. Padding- is Ëœfine tunedâ„¢ for both comfort and fit.
3. Tethers-high strength Nomex tethers secure helmet to support brace.
4. Anchoring- complete system is secured by standard 75mm shoulder straps.
The fundamental purpose of the system is to effectively form a single Ëœbodyâ„¢ of the head and torso.
By purposely directing the loads experienced following impact, the driverâ„¢s helmet is able to assist in dissipating the loads. HANS is intended to prevent driverâ„¢s head from being thrown forward in an accident, a common Ëœwhiplashâ„¢ situation which could lead to an over extension of the spinal column.
Drivers face theoretical deceleration stresses of up to 80 times the force of gravity in an accident. In such a situation, the weight of the head and helmet increases quickly from 7kg to as much as 560kg. HANS would help to absorb this strain, as well as prevent the driverâ„¢s head from hitting the steering wheel or front edge of the cockpit.
In a crash without HANS, the shoulder harness and seat restrain the driverâ„¢s torso, but only the neck restrains the head and helmet. The HANS device keeps the driverâ„¢s head from being pulled away from his upper body. With HANS, forces stretching the neck are reduced to less than one-fifth in a frontal collision as slow as 41 mph. The HANS works in a simple and elegant manner.
A CFRP yoke is worn by the driver fitted around his neck and under the shoulder belts. His helmet is loosely connected to this yoke by tethers ensuring free movement of the head. In a frontal crash, these tethers restrain the head with forces that directly counteract the headâ„¢s forward movements while the torso and HANS are restrained by the shoulder harness. By restraining the head to move with the torso in a crash, the head motions and forces in the neck are dramatically reduced. The helmet loading is also transferred from the base of the skull to the forehead- which is far better suited in taking the force.
RECENT HANS TESTING AND DEVELOPMENT
In 1997, DaimlerChrysler, Hubbard, and Downing started a cooperation to develop and evaluate HANS prototypes suitable for the FIA Formula 1 environment.
A progression of HANS prototypes were made and evaluated in many impact sled tests to develop a HANS (Figure 2) that is much smaller than the original device (Figure 1). This smaller HANS fits reclined driving positions, as is the norm in F1, CART, and IRL. Also, the smaller HANS devices have worked spectacularly well for drivers in upright seating positions such as NASCAR, ASA, TransAm, and the German Touring Car Series.
The results shown in Table 1 are from testing by DaimlerChrysler, and provide a summary of HANSâ„¢s performance in frontal crashes. These tests were run with a dummy to simulate a reclined driver with a crash sled acceleration of 45 Gâ„¢s. Figures 3 through 5 show the extreme forward motions of the helmet.
The results of the baseline test without HANS are shown in Table 1 relative to published injury thresholds used for passenger cars. Without HANS, the dummyâ„¢s head swung forward, hitting the steering wheel. The resultant load in the neck (the combination of the tension and shear loading of the neck) exceeded the injury threshold. Neck loading of this magnitude leads to fractures of the base of the skull (basilar skull fractures) that are the most common cause of death in racing drivers.
The HANS provided a dramatic reduction in injury potential. With HANS, the head was less likely to strike surfaces of the cockpit. The Head Injury Criterion (HIC) was used to assess the severity of direct head impacts. In most cases with HANS, the HIC were not applicable. Even so, HIC was reduced with HANS. Without HANS the head swung forward and, as will be discussed below with Figure 6, head accelerations due to head swinging without HANS were higher than with HANS where head swinging was restrained. With HANS, the forward motions and rebound of the head were reduced. Also, the neck loads were dramatically reduced, decreasing the potential for basilar skull fractures. Chest deflections were also reduced. As the dummy was pushed against the shoulder belts, the HANS device distributed some of the force to the shoulders and away from the chest.
Figures 3 through 5 show the extreme forward positions of the helmet during each test without and with HANS. In Figure 5, the HANS restrained the helmeted head to move with the torso (the driverâ„¢s upper body).
First, the torso slid forward under the belts and HANS until the HANS tethers were pulled straight by the forces of the helmeted head. Next, the frontal portion of the HANS (its yoke) and torso were restrained by the shoulder belts.
In a frontal test without HANS (Fig. 3), the dummyâ„¢s helmeted head hits with the steering wheel. This amount of movement may seem remarkable, but driversâ„¢ helmets often hit their steering wheels in actual crashes. The largest head accelerations and neck loads without HANS (Table 1) occurred in these tests before the impact of the steering wheel and exceeded safe limits. These excessive loads cause basilar skull fractures, which is life threatening.
With an original HANS device (Fig. 4), head motion was reduced, and head impact with the steering wheel contact was just avoided. The head accelerations and neck loads (Table 1) were significantly reduced, which is the main reason that HANS users have had no head or neck injuries.
The HANS prototype for reclined drivers (Fig. 5) reduced forward head motion by 7.5 inches compared to no HANS (Fig. 3) and by 3.3 inches compared to the original HANS (Fig. 4). This was achieved with the added benefit that head accelerations and neck loads were reduced. With HANS (Fig. 4 and 5), the helmet alignment is controlled by the tethers so the helmet stays in position on the driverâ„¢s head.
Figure 6 shows typical results from crash test with crash sled accelerations of 45 Gâ„¢s. It is a graphical summary of typical test results without and with HANS. The arrows from the top of the neck indicate the magnitudes of the components of forces that pull the head and neck apart. These arrows are drawn to scale to illustrate how much the HANS reduced these forces.
Without HANS, the head pulls the neck forward with a shearing load that slightly exceeds the injury threshold limit. The neck tension (pull) is much larger than the injury threshold limit because the head swings violently forward. Neck shear and tension combine for a total neck load that is nearly twice the injury threshold value. These large neck loads are the cause of basilar skull fractures that are the most common cause of race driver death. In crash tests without HANS, head accelerations, like neck loads, are largest due to the swinging motion of the head. The HIC injury without HANS nearly doubles that of safe levels while remaining well below them with HANS. These values of HIC are significant because without HANS, the head often strikes parts of the cockpit.
With HANS, the head is restrained to move with the torso and not to violently swing forward. Neck loads are all reduced (illustrated by the reduced length of the arrows) and the neck tension component due to head swinging is reduced the most. Head accelerations are also reduced primarily due to reductions in head swinging. HIC values are typically reduced with HANS (HIC is not applicable without helmet or head impact, and helmet impacts are typically infrequent with HANS).
Figure 7 shows frames from high-speed videos of crash sled tests from GM run at Wayne State University in 2000 to simulate a NASCAR cockpit. The sled acceleration was 45 Gâ„¢s. As in other tests without HANS, the helmet and head move forward and strike the steering wheel. Although it is not readily apparent in this frame from the high-speed video without HANS, the dummy head rotated forward inside the helmet so that the chin of the dummy was well below the bottom of the helmet. In all cases without HANS where the helmet only is in contact with the head, the head rotates toward the direction of impact and the helmet follows the head so that the helmet tends to rotate away from the impact relative to the head. In frontal impact, the head moves to expose the face and the top of the helmet eye port moves toward the top of the head.
With HANS, the helmet is restrained by the tethers, which are placed below and behind the centre of the helmet and head. Once the HANS tethers hold the helmet, the head is restrained by contact with the forehead and the helmet and head are restrained from swinging. That is, HANS helps hold the helmet and head so that they tend to stay in the normal positions.
In Figures 5 and 7, it can be seen that HANS holds the helmet and head to stay over the shoulders and the head does not swing forward as is does without HANS.
In 300angled impacts, head motions (Fig. 8) and injury measures are similar to those in frontal impacts except that without HANS the helmet hits the side of the cockpit. This impact with the cockpit suddenly rotates the helmet and the dummyâ„¢s head, which could cause head and neck injury. With HANS, the motions of the head and the impact with the cockpit edge are reduced, and the HANS tethers effectively counteract the rotation of the helmet and head. This restraint of helmet rotation would also be effective in impacts with other objects like tires or tire barriers. There is no commonly accepted threshold for head rotation, yet sudden head rotations are known to cause injury in racing. HANS reduces these head rotation injuries.
In a rear impact, the back of the driverâ„¢s helmet hits the cockpit padding behind the helmet with a high force as his body is pushed up the seatback (Fig.9). The friction between the helmet and the padding restrains the back of the helmeted head from moving with his body. The driverâ„¢s head is forced to rotate backwards (see illustration). His neck is compressed. This combination of unprotected neck bending and compression is typical of neck fractures that occur with rear impacts.
With the HANS on, its collar, rather than the helmet, impacts the pad. The friction forces are diverted onto the HANS and driverâ„¢s shoulders. Also, the HANS supports the rear edge of the helmet, reducing rotation. In rear impacts, the injurious forces and head rotation are reduced with HANS. Further, the HANS covers the back of the neck, which is otherwise exposed.
WHY NOT AIRBAGS
Daimler-Chrysler carried out a broad based review of systems capable of preventing the driverâ„¢s head impacting the steering wheel or cockpit rim, while at the same time relieving his neck of tension and shear forces generated when it attempts to decelerate his head and helmet, weighing together about 15 lbs .the two most promising technologies were an airbag that deployed from the rim of the cockpit, and was pulled across the steering wheel prior to being inflated, and the HANS device.
Theories abound concerning the viability of using airbags in the cockpit. Experts believe, however, that the triggering could be effectively controlled. But while the incredibly high speeds necessary to deploy airbags are achievable, there are key Ëœfailingsâ„¢ that make them unsuitable as a sole method of restraint.
They can be put down as:
1. They cannot be reused.
2. They contain rocket propellant.
3. Airbag can only confine movement of head itself.
4. The centre of steering wheel is level with driverâ„¢s chin. Airbag would therefore contact chin first, rotating the head.
The HANS system was selected as it is a totally passive system, and doesnâ„¢t require electronics, pyrotechnic devices, or the extensive development that would be required to prove the systems in a race environment
HANS PERFORMANCE SUMMARY
The key points of the HANS performance are:
1. In frontal impact with HANS system, the head moves with the torso to help reduce injurious head motions, accelerations, and neck loads.
2. With HANS, helmet position is controlled on driverâ„¢s head.
3. Sudden head rotation is reduced.
4. HANS improves head restraint if a driverâ„¢s helmet is struck.
5. Driver restraint is improved while accelerating, braking, in a roll-over, or rear impact.
6. HANS provides improved load spreading of shoulder belt forces in driving and in crashes.
CART mandated HANS use starting in 2000. Since CART had thoroughly documented crash injury outcomes and crash dynamics with measured chassis accelerations for several years, it was possible to study crashes without and with HANS use.
The HANS has been found to be clinically as effective in reducing the incidence of head and neck injury as hypothesized on the basis of previously reported laboratory findings. The overall experience with HANS in CART through the 2001 season was very positive with HANS reducing injuries compared to similar crashes without HANS. This positive experience with HANS contributed significantly to mandating HANS use for all CART drivers, in all series, and all driving including testing, practice, and racing.
With the recent increase in HANS use, other head and neck restraints have been offered as alternatives to HANS. Such alternatives typically use straps that come vertically up from the racerâ„¢s back and attach to the helmet. Such vertical straps do not directly resist that forward motion of the racerâ„¢s helmet and head, which leads to the injuriously large loads in the neck. These alternative head and neck restraints do share and slightly reduce the neck loading as the head swings forward, while HANS directly resists that forward motion that cause injurious neck loads and substantially reduce these loads.
In the first independent study of alternatives to HANS it was tested a baseline of no head and neck restraint, and the D-Cel, Hutchens, and HANS devices. The crash sled test conditions were: stock car cockpit, belts, and seat with a 300right front impact direction and 35 mile per hour velocity change and a peak crash acceleration of 50 Gâ„¢s.
Pictures at the left (Figure 10) show how far forward and down the helmet and head go. With the D-Cel and Hutchens devices, the helmet and head motions are essentially the same as with no head and neck restraint.
With a HANS head and neck support (bottom), the swinging motion of the head is effectively limited so the head stays in place on the shoulders and is much less likely to impact something in the cockpit.
Excessive loading of the head through the neck causes fatal basilar skull fractures.
The table below compares the loading on the neck for different head neck restraints.
It was found that the HANS device proved to give consistently excellent results in controlling neck tension forces and forward head excursions at the crash severity used in the tests. The other devices provided borderline performance in controlling neck tension forces and no significant reduction in forward head excursion at the crash severity used in the tests. These results show that HANS is the only head and neck restraint that is really effective.
Since the early 1990â„¢s, the original HANS has been used in diverse forms of racing including open wheel, sports, stock, and sprint cars, monster trucks, and power boats. The smaller and revised HANS shape, developed with the cooperation of DaimlerChrysler has made HANS acceptable to drivers in an even broader range of cockpits. Several HANS shapes have been made with different collar angles and yoke shapes to fit diverse drivers and cockpits. CART, NASCAR, and FIA F1 and other sanctioning bodies have cooperated to make drivers in all of their series comfortable with HANS in preparation for mandatory use Work to make HANS acceptable to drivers continues and is essential to broadening use of HANS.
HANS devices are mandatory in several racing series and being considered for others worldwide. Throughout the spread of HANS use, the makers have cooperated with sanctioning bodies, sponsors, teams and drivers to integrate HANS into the diverse cockpits and to make HANS devices acceptable and desirable to the racers. In this diverse implementation of HANS, HANS could always be used once appropriate accommodations were made to fit HANS into the cockpit and onto the racer. In some cases these accommodations required constructive feedback and cooperation with racers and their teams. This cooperation has resulted in a broad selection of HANS sizes and shapes and padding systems.
Only after many years of research, development and testing was the unique revolutionary system of supporting the neck from sudden impacts. And this has consistently and effectively reduced the injury potential from head motions and neck loads.
The potential of the HANS system is clear and has been recognized by racing safety and medical experts and by sanctioning body officials. Thus the head and neck support system has been made mandatory by the FIA for the 2003 Formula-1 season. Researches are being carried on for bringing a simplified, compact version of HANS into passenger cars.
1. Development of the HANS-Head and Neck support for Formula 1, Society of Automotive Engineers, SAE Publication 1998
2. Biomechanical performance of a Head and Neck Support, p-236, SAE Publication
3. Overdrive- Grand Prix, Issue No. 5
4. Overdrive, March 2003
5. Automotive Technology - Jack & Erjavec
The World Wide Web:
HANS Â¦.UP FOR SAFETY
RECENT HANS TESTING AND DEVICES
WHY NOT AIRBAGS
First of all I thank the almighty for providing me with the strength and courage to present the seminar and presentation.
I avail this opportunity to express my sincere gratitude towards
Dr. T.N. Sathyanesan, head of mechanical engineering department, for permitting me to conduct the seminar and presentation. I also at the outset thank and express my profound gratitude to my seminar and presentation guide Mr. Bilal.K and staff incharge
Asst. Prof. Mrs. Jumailath Beevi. D., for their inspiring assistance, encouragement and useful guidance.
I am also indebted to all the teaching and non- teaching staff of the department of mechanical engineering for their cooperation and suggestions, which is the spirit behind this report. Last but not the least, I wish to express my sincere thanks to all my friends for their goodwill and constructive ideas.