|Assuring a rational level of driver safety
By Richard Strout and Curt Tucker
By focusing solely on the question of safety harness failure, investigators and decision makers who act on the conclusions of those investigators can miss the point. The issues surrounding materials, design, installation and quality/reproducible performance are still being examined. The inherent assumption seems to be that if the harness breaks, it isnt doing its job.
Instead, it can be argued, if the harness fails but the driver survives, the system has worked. In reality, failure can be a harness that stretches without breaking and injures the driver; while success may be a harness that tears after attenuating the g-loading long enough to protect the driver from traumatic injury or death. The pass-fail nature of the current specifications do not address individual components in the harnesses. The authors conclude from a series of crash tests conducted in the summer of 2002, there is enough variation in the real world of safety harness systems to call for more standardization in the manufacture and installation specifications.
Although most drivers would prefer a safety system that is transparent and invisible until the microsecond before it is needed, allowing the driver to function in a comfortable, focused and unimpaired fashion, the reality is that the environment is increasingly constraining. For it to be effective, the seat must perform most of the work of supporting the driver laterally, must stay locked in position and must preserve the correct angles of the seat and shoulder belts to hold the driver as a unit with the seat. The harness serves the purpose of locating the driver in the seat and keeping him comfortable while he does his job. The seat locates him within the car. Harness belts must be tight, both to keep the drivers body from accelerating into hard objects (or relative to the seat or harness) and to prevent sliding around under acceleration and deceleration. In addition, the seat and the seatbelt must be relied on to work continuously the only elements of the entire safety system that must do so.
Recognizing the compromises that must be made to the idea of the perfect safety system, what are the critical elements of design, including materials, manufacture, and installation? As the amount of field data collected by CART, NASCAR and others grows, the authors expect further refinements and possibly fundamental changes, based on what is clear from even casual observation: that what actually happens in a crash is different from the controlled impact of a test sled. Just as investigators began studying the results of angular impacts when real life crashes were examined, we expect that safety harness specifications will soon start to dictate that restraint systems must be designed, fabricated and installed in keeping with the new knowledge gained by the much needed research and investigation. Our own research data raises specific questions our proposed safety harness task force should address. These include Quality Control/ Reproducible Performance, Materials (webbing, hardware, etc.), Design, and Installation.
Quality Control/Reproducible Performance Safety board inquiries in F1, CART and NASCAR have explored various aspects of the role the safety harness/driver restraint system plays in reducing driver injuries and death. On-board data logging in FIA and CART has added invaluably to the improvement of all driver safety systems by providing hard data on the forces sustained by the driver and his environment. The MSEC paper presented in 1998 by Ford engineers Weerappuli, Sin and Stanecki outlines the parameters defined for CART. Wayne State University has developed shoulder belt load cells that can be integrated with Delphi ADR-2 data recorder for track testing to supply real data for verifying such existing mathematical models as is not currently supplied by on-board accident data recorders. This ongoing research, with the contributions that will come from the black boxes in NASCAR Winston Cup events, will build on the landmark deceleration injury assessment criteria research conducted by SAF Col. Stapp and others, and bring us farther along the development of protective systems. But that, by itself, is not enough.
First, the manufacturers of safety equipment, racing seats and chassis must cooperate on the definition of quality standards. While the comprehensive scope of QS-9000 (QS-9000 is derived from ISO 9001, with additional requirements that are particular to the automotive industry) standards for ensuring a process that produces consistent high quality is familiar to anyone working in the Big Three auto-maker contracting environment, this type of rigor is not enforced but would be welcome in the authors view in motorsports. Remember that less than 40 years ago, driver restraint systems, firesuits and reinforced/padded tubs were virtually non-existent. It was just 20 years ago that CART Chief Steward Wally Dallenbach organized the CART safety committee that has overseen dramatic safety improvements, such as the reinforced foot box which has reduced leg, foot and ankle injuries. But there are several aspects of safety harness construction/installation still requiring investigation.
The American Society for Quality makes an excellent case in suggesting that QS-9000 rigors might have helped avoid the recent history leading to the sport utility tire recalls. Inspectors, technicians, engineers, auditors, and others work from design through final inspection to ensure the quality of the finished product, they note. By monitoring processes and then analyzing the data, they can see when [and where] things are going wrongthat is, when a process is out of controland then take corrective action. While recognizing that the product standards and quality-driven management disciplines do not guarantee zero-defects, the discipline and the specifics of quality control are still the best first line of prevention.
The authors believe that by reaching a consensus among the manufacturers of harnesses, driving seats and racing chassis, for more stringent SFI standards and inspection processes adopting QS-9000 standards in harness manufacture, a rational measure of safety system effectiveness can be realized, hopefully before further loss of life.
Sad as it is to say, loss of life inevitably provides the turning point for implementing improvements; and the sport has reached that juncture again. Following the double fatalities at Imola in 1994, the FIA expanded the safety harness specification to increase the width of the main seatbelt from 50mm to 75 mm (a decision the SFI Committee, stateside, endorsed in the mid-1980s). The result was to reduce deceleration impact of the drivers chest (in HyGe sled tests) from 61G to 41G.
Huge advancements were made in NHRA safety when quality and safety standards were demanded by the sanctioning bodys insurance company - - or else.
The authors call for a task force of all interested parties to achieve this same objective before an outside power makes all the decisions for us. Many sanctioning bodies rely upon the SFI 16.1 specifications to define the driver restraint package, design dimensions and pass-fail requirements. The SFI 16.1 standard describes the testing procedures for compliance in detail, and explains how to interpret the test data to determine if the harness or manufacturer may be SFI-certified. Recognizing that the existence of standards does not guarantee performance in the real world, we believe that the inspection process should be re-evaluated to ensure that the test samples submitted to the SFI for review are an accurate representation of what is sold off the shelf. Further, we recommend that the sanctioning bodies insist on physically inspecting all safety gear, and underscore the need for a joint committee of harness, seat and chassis manufacturers, as well as sanctioning body inspectors, working together to see that such a scenario is possible. Current installations make it virtually impossible for a tech inspector to evaluate the belt installations without removing the seat an impractical process that can take over an hour. Ironically, recent seat design and installation developments to increase safety have compounded the access, and belt performance, problems.
In six and a half years as a test engineer at a independent lab contracted to SFI, the co-author observed hundreds of review tests. Restraint harness design criticality falls into three areas: material, design and the installation environment. This balance of this paper will look more closely at these three areas in the context of the results observed in a series of crash tests recently conducted at a major car manufacturers test facility.
Materials What actual operating environment do safety harness system materials, design and installation face? While much investigation, design engineering and test analysis have focused recently on head and helmet restraints to reduce the recurring incidence of HIC, the safety harness is still the first line of defense, as recent investigations such as the Earnhardt inquiry suggest.
The SFI 16.1 standard specifies that for certification, a driver safety harness must be constructed of 6.6 nylon webbing that meets the minimum width-standard under load. However, webbing thickness, weave density and assembly thread weight, stretch and stitch count are equally critical in determining how the webbing will perform under impact.
In the FIA, all harnesses are subjected to the European road safety legislation ECE R16 test using a test dummy and sled in measured acceleration and deceleration scenarios as well as static tests of the webbing and components which have been subjected to environmental preconditioning. Although the webbing is an industry standard material, harness hardware such the release buckle, adjusters, etc. are built to individual design specs.
SFI 16.1 is a performance standard for the production of the safety harness hardware. Currently, it does not specify alloys to be used, treatments such as de-burring the stamped pieces, nor does it define the design the manufacturer takes for his dies. We believe such specifications should be mandated, given the evidence provided in crash testing. Load testing demonstrated that not only do sharp edges on adjustment hardware cut the webbing under load, the placement of the belts is critical to how the load is distributed on that hardware. Radius-increasers wherever the webbing might chafe on the hardware extend performance. Superior performance results where harness manufacturers employ CNC machined steel and then tumble the parts to remove burrs and sharp edges. These elements are just as important to the useful life of the harness as monitoring UV-exposure and material heat treatment. Even though SFI mandates the inspection and re-webbing of race harnesses every two years because outdoor exposure can diminish the strength of the webbing by as much as 50 percent, variances in hardware can diminish effectiveness by as much as 100 percent. Mounting hardware is equally critical, and requires that we define clear performance criteria to guide the selection of materials and dimensions for installation hardware.
The authors similarly wish to encourage a forum for discussing standards for the actual harness assembly process. A QS-9000 type discipline would define the necessary parameters for thread weight and tension, stitch count and pick-up, and the diameter, shape, length and velocity of the needle used to stitch the webbing, as well as what procedures to take to maintain quality when the manufacturing process is interrupted. For example, too high a speed on the needle produces heat that can melt the thread. Whether using computer-controlled stitching heads or individually operated sewing machines, these elements are critical to the effectiveness of the final product. Without standards for these areas, there are examples such as one major manufacturers recent attempt to implement a z-fold design whose stitching was engineered to fail in the course of helping to attenuate impact. The concept would have benefited from additional scrutiny, to consider the effects of multiple hits, for example.
For anyone familiar with cloth fabrication it is obvious that even the webbing can be a substantial variable. It is well known that southern US sun can sap the strength of nylon webbing by as much as 73 percent in just one seasons exposure. This is one of many reasons why most sanctioning bodies require that racers harnesses carry certification showing that they have been newly purchased or have been inspected by the manufacturer within the past two years. There is also still latitude in the spec for the webbing itself. Currently, some -- but not all -- harness manufacturers have adopted internal procedures to ensure quality control on the webbing by insisting on test-based proofs from their suppliers. Willans uses only three webbing suppliers to maintain quality consistency. TeamTech sends a sample from each supplier lot to an independent test facility and/or requires the manufacturer to submit independent test results. Stricter standards would provide greater assurance across all systems.
Design As Carroll Smith states so cogently, The sequence of events in any crash is deceptively simple: first the car impacts, then the driver impacts against the car and finally the drivers internal organs impact against the drivers skeletal/muscular shell. Therefore the basic problem in driver safety is management of impact energy. The energy has to be either dissipated or absorbed by something the object is to protect the all-important soft parts by dissipating energy through the vehicle components and the seating environment. The authors would add and through the parts of the human body best able to withstand the shock as this amendment serves to remind us of the importance of design and installation.
To convert, or dissipate any level of potential energy, one must work within the constraints of time and surface area. The human body is designed to absorb energy over large areas, most especially the broad muscles of the back and chest and their supporting skeletal framework, rather than the soft flesh and muscular tissue. Because water is not compressible, the human body attenuates impact as long as it can spread the load and avoid internal crushing. As the crash tests demonstrated, the placement of the belts is critical. Improper installation can allow a seat belt to move in a crash where it can cause fatal injury to internal organs. Too often, harness placement solutions are forced by the design and construction of the seat or chassis.
Although the international racing arenas have long since rejected the latch-lever buckle and the 5-point harness, stock car racers are now slowly adopting improvements, including 6-point harnesses. Research on 5,6,7, 8, 9, and even 11-point harnesses has been ongoing since the early 1990s.
The 6-strap safety harness under discussion is the one on which the Ford/CART mathematical model is built: six belt segments, two for each region of constraint, i.e. shoulder, lap and crotch. The shoulder and lap belts are 76.2 mm (3 in) wide and the crotch belts are 44.45 mm (1.75 in) wide. All belt segments are attached to a quick release buckle.
A review committee could more effectively evaluate current designs as well as alternatives such as harnesses similar in function to rappelling harnesses. These use adjustable anti-submarining straps that wrap around the upper thigh of each leg and attach to the buckle, allowing zero forward excursion of the pelvis under the lap belt as well as giving the driver more control and leg movement and preventing pivoting of the pelvis in the seat. Pelvic pads can help position the driver while enhancing the shock absorption qualities and attenuating impact loads by spreading them over the heavy bone structure of the pelvis.
The effect of properly designed and installed safety harnesses on driver performance is another aspect for investigation. Logic dictates that the better a harness can locate and secure a driver in his seat, the better a pilot he becomes.
Enhancements that help locate the harness, such as sternum straps and chest/pelvic pads decrease the lateral and forward movement of the upper body. Also, users report that the padding system allows the harness to be adjusted so tightly, without discomfort, that the driver feels as though he is part of the car.
Installation At least half of the job of the safety harness is to locate the driver relative to the car. If he slides under the buckle and ruptures his stomach or spleen, the likelihood of fatality can be just as high as if his head hits the steering wheel with a force higher than the 60G survivability index.
In keeping with the concept of an effective seating environment, the authors tend to agree with Dr. Brock Walker if the torso is properly positioned and restrained, the shoulder harness stretch will allow the helmet to strike the steering wheel [preferably an impact-absorbing, steel spoke steering wheel/column structure] before serious damage occurs
[with] the end result of even the most terrifying-looking forward neck flexion
[being] a sore neck.
The shoulder harness must keep the driver vertical, without adding compression forces to his spine. Popular articles suggest anchoring the shoulder belt anywhere between 5 degrees below and 30 degrees above the drivers shoulder. However testing demonstrates the importance of having the shoulder strap anchor positioned at an angle of 90 degrees relative to the seat back, or no more than 10 degrees above the shoulders, recognizing that any downward angle can cause dangerous spinal compression.
Similarly, there is little latitude for positioning the crotch strap. The anti-sub-strap must never leave contact with the drivers body. If it extends forward, leaving a gap between the crotch and the strap, the harness will lift away from the driver, leaving him loose in the seat.
The lap belt must tightly contour an unobstructed 180 degrees of the drivers pelvic area at a point just below the anterior iliac spine. The racer needs a 6-point harness with anti-submarine straps that encircle the thigh, or straps with a 30-degree rearward angle or less across the thigh and seat, restraining the pelvis. The belts both keep down-load on the shoulder belts and control the movement of the thigh and pelvic area, a requirement we noted was especially necessary when walking a wall backwards in an crash.
In particular, the author found that lap belt installations that pass the belts through slots in the seat can prevent the proper load distribution because they curtail the movement of the belt to accommodate the load. When this happens, the hardware rotates so that it chafes and eventually cuts the webbing. When the belt passes through a slot so that it cannot stay in line with the mounting point under load, the pivot point causes the webbing to dump its load while at the same time the twisted webbing works over the knurling and onto the flat of the hardware, initiating a cut that expands, under further load, into a tension tear.
Strap and mounting fasteners and related hardware are currently under review. Just as there are no specifications for the hardware itself, as to grade or size, there are no guidelines for dictating structurally sound mounting procedures. Field application varies; for example, an entire safety belt system often comes down to a single shear tab rather than the double we would recommend.
Still, many teams weld bolt-in hardware or eye-bolts for snap-in hardware to the floorboards or roll-cage, instead of, for example, a mounting tab on the roll bar with an adequate-sized hole to accommodate the shaft of the eye-bolt. The former can significantly weaken these structures if improperly welded.
The test results demonstrate that seat belt access slots be permitted only for the two shoulder straps and the one or two anti-submarining belts. The seat sidewall should have low pocket contours so the lap belts pass over, not through, the seat. There are many seat designs with only one access slot for the shoulder belts. Installing both belts through the one slot causes the webbing to dig into the drivers neck, thus prompting him to wear his shoulder belts too loose. Adequate separation of the shoulder belts at neck height is necessary.
The testing demonstrated that Sprint car-style right-side head nets are effective in all types of racing not only for helping contain the head within the seat confines, but also for increasing lateral seat location. The issue of head guards and nets is another that invites further testing and participation by their manufacturers in the debate. The interaction of helmet, head guards, restraints and harnesses what stays in place, what slips, and when -- are all considerations that must be incorporated in the total rational approach.
One cannot separate the seat from the seat belt installation in creating the ideal seating environment for driver safety. We have not addressed seat material, design or installation issues; although we feel, in many cases, that the padding in racer seats is too soft and seat frames too flexible to help in properly absorbing the loads.
We need to clean up the wording on the specifications and communicate with the tech inspectors. Much latitude has been allowed previously in these criteria and in the inspection processes. More attention to material, design and installation of the components, and increased training for, and focus by, tech inspectors in this area would effectively improve the protection even existing harness/seat systems provide. Fortunately, the safety design engineering debate evolves as sanctioning body safety boards and private enterprise continue to test and refine new safety harness prototypes. As Paul Lane observed in his report on new safety developments in CART, Information on a non-competitive related subject such as safety technology is informally and quickly disseminated among the experts within sanctioning bodies, industry and racing teams Such cooperation and international communication is essential. So is continued development and refinement of the standards and of the quality process enforced by the manufacturers involved. The authors welcome an aggressive schedule for moving forward such discussions by the key forces involved.
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