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Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant a
b
a
David C. Viano , Roger Burnett & Chantal S. Parenteau a
ProBiomechanics LLC, Bloomfield Hills, Michigan
b
Ford Motor Company, World Headquarters, Dearborn, Michigan Accepted author version posted online: 16 Jan 2014.Published online: 12 Jun 2014.
Click for updates To cite this article: David C. Viano, Roger Burnett & Chantal S. Parenteau (2014) Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant, Traffic Injury Prevention, 15:7, 726-733, DOI: 10.1080/15389588.2013.879124 To link to this article: http://dx.doi.org/10.1080/15389588.2013.879124
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Traffic Injury Prevention (2014) 15, 726–733 C Taylor & Francis Group, LLC Copyright ISSN: 1538-9588 print / 1538-957X online DOI: 10.1080/15389588.2013.879124
Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant DAVID C. VIANO1, ROGER BURNETT2, and CHANTAL S. PARENTEAU1 1
ProBiomechanics LLC, Bloomfield Hills, Michigan Ford Motor Company, World Headquarters, Dearborn, Michigan
2
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Received 25 September 2013, Accepted 23 December 2013
Objective: The impact force to the head and neck were measured in sled tests with and without inflation of a combo airbag for a far-side occupant to determine the risk for basilar skull fracture. Methods: Sled tests were run at 24 and 32 km/h (15 and 20 mph) with and without inflation of a combo side airbag to analyze the effect of cross-car diving into the side interior. The matched tests involved one pair at 24 km/h and another at 32 km/h. The 24 km/h pair involved a lap–shoulder-belted 5th percentile female Hybrid III and the series at 32 km/h involved an unbelted 5th percentile Hybrid III. The dummy was ballasted to 69.5 kg (153 lb) and laid on the right side. The dummy was positioned 30.5 cm (12) from the far-side interior to ensure the full sled delta V occurred before head impact. The buck consisted of a 2001 Ford Taurus. The combo thorax–head side airbag was stored in the seatback. The airbag was triggered about 120 ms before the head impact. The head, chest, and pelvis were instrumented with triaxial accelerometers and the upper and lower neck, thoracic spine, and lumbar spine had transducers measuring triaxial loads and moments. High-speed video recorded different views of the dummy motion. Dummy kinematics and biomechanical responses were compared to study the influence of inflating the side airbag on the head and neck. Results: The top of the head impacted the far side. The force of impact was similar with and without the airbag as the head compressed the airbag and loaded the vehicle interior trim behind the airbag. The peak force on the head was primarily from neck load as torso augmentation occurred. For the 24 km/h (15 mph) tests, the peak force was 4.7 kN (1055 lb) without and 4.8 kN (1088 lb) with the airbag and there was over 2.67 kN (600 lb) of lap belt load. The peak head acceleration was 93 g without and 72 g with the airbag. For the 32 km/h (20 mph) tests, the force on the head was 15.3 kN (3433 lb) without and 15.2 kN (3406 lb) with the airbag, although the instrumentation saturated. The peak head acceleration was 236 g without and 262 g with the airbag. Conclusion: The airbag reduced head acceleration in the belted test but did not influence the diving forces from torso augmentation through the neck of the far-side occupant. The side airbag did not reduce the risk for basilar skull fracture due to high neck compression loads in either the belted or unbelted tests. Keywords: side impact, head injury, torso augmentation, basilar skull fracture
Introduction Far-Side Occupant Injury In a side impact, the vehicle is accelerated laterally by the collision. The side interior may be pushed inward depending on the severity of the crash and shape and stiffness of the impacting vehicle. The occupants will move laterally relative to the vehicle interior depending on the pulse and direction of force. The motion is influenced by forces from the interior or other occupants. For example, if the occupant’s lower body interacts with Associate Editor Clay Gabler oversaw the review of this article. Address correspondence to David C. Viano, ProBiomechanics LLC, 265 Warrington Rd., Bloomfield Hills, MI 48304-2952. Email: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gcpi.
the center console, the upper body may bend sideways. For farside occupants, contact is initially made with the center console or restraint system, followed by the occupant leaning and stretching toward the far-side interior (Gabler, Digges, et al. 2005; Moffat and James 2005; Douglas et al. 2007). Far-side occupants have more interior space to travel before contacting the far-side interior than near-side occupants. This allows more energy to be absorbed by the restraint systems, but movement in the interior can increase the speed of the occupants head when it contacts the far-side interior. The greater the distance the far-side occupant can travel, the more time there is for the vehicle to rotate and move relative to the occupant. As a result, the influence of the vehicle’s motion and intrusion differs between far-side and near-side occupants. Other factors influence occupant kinematics such as the belt fit and geometry. For the far-side belted occupant, the upper torso may slide out of the shoulder belt and strike the adjacent occupant or intruding structures.
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Impact Force to the Head With Side Airbag Far-side occupants account for 30% of injuries in real-world side impact crashes (Fildes et al. 2000). Fildes et al. (1994) carried out an in-depth study and showed that the frequency of Abbreviated Injury Scale 3+ head injury was greater in far-side than near-side impacts. Head injury was the most common injury type in far-side occupants (Fildes et al. 2007). Horsch et al. (1979) and Horsch (1980) documented occupant excursion in far-side impacts. Postmortem human subjects and dummies were in 35 km/h (21.7 mph) and 10 g sled tests with a lap and lap–shoulder belt in near- and far-side sled tests. The far-side occupant’s upper torso moved laterally and rotated about the restrained pelvis toward the adjacent seat. Table 1 summarizes some of the far-side occupant excursions in the literature. The lateral excursion was about 64–69 cm (25–27) in 24–31 km/h (15–17 mph) delta V far-side impacts. The time is approximately how long it took to reach the far side. Peak belt loads are listed.
Side Airbags Side airbags are primarily designed to protect near-side occupants in side impacts. There are thorax or torso-only airbags, torso–head airbags (combination airbags), and separate torso and head airbags such as an inflatable tubular structure or roof rail curtains. Side airbags are evolving with longer inflation times with coated airbags for rollover protection and to reduce ejection risks. Side airbags are effective in reducing side-impact fatalities for near-side occupants. McCartt and Kyrychenko (2007) reported a 37% reduction for head airbags and 26% reduction for torso-only airbags. Braver and Kyrychenko (2004) reported a 45% reduction for head–torso combination airbags and an 11% reduction for torso-only airbags. These results address near-side occupant fatality reductions with side airbags and include changes in the vehicle side structures to lower the velocity of side intrusion and provide space for the inflating airbags. Kahane (2007) found that torso and head airbags reduced fatality risks by 24% for near-side occupants. He also assessed the effectiveness of side airbags for far-side occupants and reported no fatality reduction with the torso–head combination side airbag for far-side occupants. The requirements for side airbag sensing are more stringent than for frontal airbags because of the reduced space between the occupant and the striking object in side impacts, the limited side interior space and structures, and the shorter detection and inflation times. Zhang et al. (2004) reported that side impact sensing needs to discriminate a crash condition warranting inflation within 6–13 ms compared to 15–25 ms for frontal impact sensing. Airbag inflation times for side impact airbags range from 20–30 ms compared to 45 ms for frontal airbags. Bostrom et al. (2008) discussed measures to improve the protection of occupants in far-side impacts. They demonstrated the effect of a coated side curtain in a 50 km/h (31 mph) delta V side impact. At 50 ms, the postmortem subject was supported by the high center console and belt system, but the force of the impact caused the upper body to rotate toward the far-side interior. Intrusion was simulated by mov-
727 ing the interior closer to the center of the vehicle to represent deformation from an Insurance Institute for Highway Safety high-hooded barrier impact. The far-side interior was located 60 cm (23.6) from the occupant’s head. Head contact with the inflated curtain occurred at about 100 ms. In this test, the position of the head was relatively high, since the occupant leans across the passenger seat and is somewhat upright. The head loaded the curtain above the beltline in the area of the side window. With less intrusion, the occupant leans more toward the far-side, stretches, and dives into the side interior below the beltline. As the occupant’s head contacts the far-side interior, inertial forces on the neck increase by torso augmentation. As the occupant dives into the far-side interior, the head stops but the torso keeps moving toward the head.
Torso Augmentation (Diving Injuries) The effect of torso augmentation on neck loading is well documented in the literature. Moffatt (1975), Orlowski et al. (1985), Bahling et al. (1990, 1995), and Moffatt et al. (1997) discussed the occupant diving into the roof during rollovers with the vehicle inverted. During an inverted drop, the head contacts the roof and stops while the torso continues to move downward. This causes a “diving” mechanism of neck loading on the basilar skull (McElhaney et al. 1979; Pintar et al. 1990, 1995). The neck is loaded from the head impact force and torso inertia. Spine or head injuries can occur depending on the vertebral strength and location, torso mass, and impact of force (Nightingale et al. 1996; Pintar et al. 1995; Viano and Parenteau 2008). Torso augmentation can also occur as the body moves downward with an underbody impact to a vehicle causing lumbar compression and burst fracture (Molz et al. 1997).
Basilar Skull Fractures McElhaney et al. (1995) investigated a series of drop tests with cadavers exposed to cranial loading. They reported that basilar skull fractures result when the head is “constrained on the impact surface and the inertia of the torso drives the vertebral column on the occiput” (p. 669, abstract). These findings are consistent with prior research showing that basilar fracture can occur with or without upper cervical injuries due to impacts on the top of the head oriented down the axis of the neck, where the inertia of the torso leads to neck compression forces (Alem et al. 1984; Myers and Nightingale 1999; Sances et al. 1986). Head impacts combined with inertia loading by the torso can lead to head or neck injuries in rollover and other crashes (Bambach et al. 2013) and spearing tackles in football (Bartsch et al. 2012; Viano 2012; Viano et al. 2007; Viano and Pellman 2005). The injury occurs in the cervical spine, base of the skull, or both depending on a number of factors. Parenteau and Viano (2011) assessed the risk of basilar skull fracture by crash type. They reported that basilar skull fractures more often occurred in rollovers and in side impacts. The most common contact source was the roof, side rails, and header in rollovers and the B-pillar in side impacts. The
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Table 1. Summary of far-side dummy excursion tests Excursion Max (cm) 64 (head) 47 (neck base) 61 (neck base) 69 (head)
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aS
Time (ms)
Barrier
Delta V estimate (km/h)
Belt load (N)a
Reference
140
ECE R95
31 35 35 24
S: 1202 L: 2799 S: 6822 S: 3600
Stolinski et al. (1999) Horsch (1980) with bucket seat Horsch (1980) with bench seat, timing from Horsch et al. (1979) Bostrom et al. (2003)
120 125
= shoulder, L = lap.
authors highlighted the benefit of seat belts. Compared to belted occupants, the relative risk is 9.0 times higher for unbelted, near-seated occupants and 16.3 times higher for farseated occupants. Basilar skull fractures are sometimes associated with large forces and short impact durations (Alem et al. 1984). Alem et al. (1982) carried out 10 kg (22 lb) impact tests on the crown of 14 cadaveric heads at 7 to 11 m/s (15.7–24.6 mph). A basilar skull fracture was observed at 15 kN (3372 lb) with 3 ms duration and 0.5 cm padding at 9 m/s (20 mph). They compared their findings to an earlier test (79H200) where a basilar skull fracture occurred after a 12 m/s (26.8 mph) impact with 2.5 cm (1)-thick pad. The results suggest that padding, particularly thick padding provided by a side airbag, may not lower the risk of basilar skull fractures in vehicle crashes. The objective of this study was to determine the effect of side airbag deployment on head and neck biomechanical responses using matched side impact tests with and without side airbag deployment.
Methodology Sled Buck and Setup Four sled tests were conducted at the Ford Safety Center in Dearborn, Michigan, with 2001 Ford Taurus bucks. The 2 unbelted tests at 32 km/h (20 mph, H32534 and H32534) were run on February 12–13, 2013. Two belted tests at 24 km/h (15 mph, H32555 and H32556) were run with another 2001 Taurus buck on March 1–2, 2013. The same setup was used for each series with a 5th percentile female Hybrid III dummy (Backaitis and Mertz 1994) ballasted to 69.5 kg (153 lb) lying on her right side on the driver’s seat. The sled test is representative of a side impact to the rear door and wheel area that does not deform the B-pillar but causes high delta V . The study was motivated by a real-world case of this type where we were interested in whether the side airbag could have helped prevent a fatal basilar skull fracture with head impact on the side interior below the beltline. Though intrusion is a factor in many far-side collisions, there will be some impacts where the occupant compartment remains intact and the far-side occupant stretches toward the side interior with a head impact on the door trim or B-pillar. The Taurus was aligned at 108◦ on the sled to simulate a side impact at less than 4 o’clock principal direction of force. Appendix 1 (see online supplement) shows the pretest setup. The dummy was placed on the right side on a low-
friction sheet of Teflon with 0.3 cm (0.125) thickness resting on a 15.2 cm (6) thickness of dense foam. This allowed the dummy to move toward the far-side interior. The height of foam aligned the head impact with the B-pillar trim below the beltline. It approximated the height of the armrest or center console as the occupant leaned toward the far-side interior. The setup positioned the head in line with the B-pillar below the beltline on the far side and centered on the inflated combo side airbag (head and chest airbag) deployed from the seat. The dummy was place 30.5 cm (12) away from the interior so the full delta V from the sled acceleration occurred before contact on the far side. The side airbag was triggered before the sled acceleration to approximate a head contact at about 120 ms, consistent with the time for a driver to reach the farside in a severe side impact. The B-pillar was undeformed and did not simulate intrusion that can occur with side impacts on the doors. The top of the dummy’s head was painted to determine contacts during the test. The sled tests involved a short-duration pulse to ensure that the full delta V occurred before head contact on the far side. The 32 km/h (20 mph) tests involved 41 g peak sled acceleration. The 24 km/h (15 mph) tests involved 20 g peak sled acceleration. High-speed cameras photographed occupant kinematics and the head impact on the far side. The 5th percentile female Hybrid III dummy was instrumented with an array of transducers to measure head triaxial acceleration, upper and lower neck moments and forces, thoracic spine moments and forces, lumbar spine moments and forces, and triaxial chest and pelvic acceleration. The triaxial accelerometers at the head center of gravity were used to determine peak resultant head acceleration, HIC15 and HIC36 . The spinal transducers measured upper and lower neck responses and lower thorax and lumbar responses. The 6-axis load cells measure axial tension–compression, lateral and fore–aft shear forces, and flexion–extension, lateral and rotation moments. Lap belt load was measured in the two 24 km/h (15 mph) tests. The belt load was measured at the outboard lower anchor.
Instrumentation and Filtering Sled acceleration (Endevco 7264B-500) was measured according to the SAE J211-1 and filtered to channel frequency class (CFC) 60 (Society of Automotive Engineers [SAE] 2003). The delta V was determined by integration of the sled acceleration using CFC 180. The maximum time for data collection was 300 ms. The Hybrid III dummy data were recorded according
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to SAE J211-1 (SAE 2003). Filtering was done on the dummy responses with CFC 1000 for head, CFC 180 for spine acceleration, CFC 1000 for neck force, and CFC 600 for neck moments. Upper neck moments were corrected with the neck force to report occipital condyle moments in accordance with SAE J1733 (SAE 1994). Impact Force
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Impact force (F) in the z direction was determined for the head. The diving motion of the dummy was into the far-side interior and involved forces down the axis of the neck and spine. Impact force in the z direction (Fz ) involved the head acceleration in the z direction (az ) and the upper neck force in the z direction (FNz ): Fz = mhead az + FNz ,
(1)
where mhead is 3.68 kg (8.1 lb) and includes the mass of the Hybrid III head (3.34 kg) and the mass of the upper neck load cell above the sensing element (0.34 kg). The combo head–thorax side airbag used in these tests was an option for the 2001 Ford Taurus. The side airbag was developed for the regulated 53.9 km/h (33.5 mph), 27◦ crabbed movable FMVSS 214 barrier and for the 50 km/h (31 mph)km/h deformable 90◦ ECE R95 barrier impacts on the front door. The side airbag was designed for near-side occupant protection.
Results Figure 1 shows side-by-side images from the high-speed video of tests H32555 (left images with no airbag) and H32556 (right images with airbag) at nominally 24 km/h (15 mph) delta V with a belted dummy. Test setup photos can be seen in Figure A1 (see online supplement). In these tests, the sled was triggered at 55 ms and acceleration was over at 110 ms. The side airbag was remotely triggered at 25 ms. The airbag can be seen starting to deploy out of the seat at 25 ms and it is fully inflated at 58 ms. The dummy contacts the airbag at about 124 ms and deforms it into the B-pillar with a spike in head acceleration at 148 ms. The impact causes the neck to compress as the torso moves toward the far-side. Without the airbag, the dummy rebounds toward the driver seat, away from the principal direction of force. With the airbag, the head is pushed forward toward the instrument panel causing neck flexion. Figure 2 shows the force on the head in the z direction. The dotted line is with the airbag and involves an earlier loading of the head, although the peak force is nominally the same. The peak force was 4.7 kN (1055 lb) without and 4.8 kN (1088 lb) with the airbag. With the airbag inflated before the sled acceleration, the dummy’s head contacted the airbag and compressed it into the side interior trim. This did not influence the neck compression force. There was more than 2.7 kN (600 lb) of lap belt load. The complete set of peak responses is provided in Table A1 (see online supplement). The peak occupant biomechanical responses were normalized to
Fig. 1. (a) Side-by-side images of the side airbag inflation and occupant impact on the far side in sled tests H32555 (left, no airbag) and H32556 (right, with airbag). (b) Side-by-side images of the side airbag inflation and occupant impact on the far side in sled tests H32555 (left, no airbag) and H32556 (right, with airbag). (Continued)
the 5th percentile dummy injury assessment reference value (IARV) provided in Mertz et al. (2003). For comparison, the 32 km/h (20 mph) tests had a peak force on the head of 15.3 kN (3433 lb) without and 15.2 kN (3406 lb) with the airbag in the z direction, although the instrumentation in the upper neck saturated, so the actual load was higher. Figure 3 shows other biomechanical responses from the 24 km/h (15 mph) tests with a belted dummy. The resultant head acceleration shows the head impact on the B-pillar. It is lower with the airbag and occurred earlier. The peak resultant acceleration was 93 g without the airbag and 72 g with the airbag. The upper neck compression shows about the same level of peak load. The resultant chest acceleration was 29.7 g without the airbag and 30.7 g with the airbag. The upper neck flexion moment is higher with the airbag as the head is deflected forward, causing more neck flexion than with the airbag.
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Head Impact Force (N)
5,000
0 0
50
100
150
200
250
300
Time (ms)
-5,000
-10,000
-15,000
H32534 (no airbag) H3253 (airbag)
-20,000
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Fig. 2. Head impact force (Fz ) in the 24 km/h (15 mph) tests with and without a side airbag.
Fig. 1. (Continued)
Several peak responses are above IARV for the 5th percentile female dummy. The upper neck compression force was 214% of IARV with the side airbag and 207% without the airbag in the 24 km/h (15 mph) tests with a belted occupant. The upper neck flexion was 189% with the airbag and 108% without the airbag. The upper neck compression force was 531% of IARV with the side airbag and 531% without at 32 km/h (20 mph) tests with the unbelted dummy. Figure A2 (see online supplement) shows posttest photos with chalk transfer associated with head impact on the far-side B-pillar in test H32555. The chalk transfer can be seen on the airbag in Figure A3 (see online supplement) with test H32556. In the right photo, the airbag has been pulled up to show the chalk transfer to the center of the side airbag.
Discussion The matched tests show that the side airbag does not reduce upper-neck compression forces at the base of the skull, even
when the dummy was lap–shoulder belted and there was over 2.7 kN (600 lb) of belt restraining load. The review of the test video highlighted the “torso augmentation” mechanism that occurred in the far-side impact. The occupant dives toward the side interior with the torso augmenting the loading of the neck at the base of the skull. This mechanism of injury to the basilar skull or neck has been well documented in motor vehicle crashes and sports. The compression forces in the upper neck load cell were 5.3 times tolerance in the 32 km/h sled tests and over 2.0 times in the 24 km/h tests (Table A1). The actual peak load in the unbelted test was not determined as the load cell saturated. Both series showed a high risk for injury due to neck compression based on human tolerances (Mertz et al. 2003). In the 24 km/h tests, the side airbag reduced the peak head acceleration; however, in the higher velocity tests, the airbag was not sufficient to dampen the head acceleration as the head quickly compressed the airbag and loaded the side interior. In both series, the head rebounded off the side interior while the torso was still diving toward the interior. In the lower speed tests, the airbag caused the head to displace forward, flexing the neck and allowing head contact on the instrument panel. Without the airbag, the head rebounded off the side interior. The full dummy tests show that the inflation of a far-side combo airbag does not alter the risk for basilar skull fracture. The tests also show that the airbag can redirect the head forward and cause neck flexion. Though the peak head acceleration is lowered somewhat with the airbag in the belted test, the forces at the base of the neck are not influenced and the airbag can increase neck flexion and lateral bending. There is currently no regulation to assess far-side occupants in side impacts. Research groups have been working on far-side occupant protection because of the involvement in serious-to-fatal injury (Digges and Dalmotas 2001; Digges and Gabler 2006; Digges et al. 2005; Fildes et al. 2000; Frampton et al. 1998; Mackay et al. 1991). In 2004, an international consortium was formed to assess far-side occupant kinematics and injury (Fildes et al. 2005; Gabler, Fitzharris, et al. 2005). The objective of the consortium was to develop representative test conditions, injury criteria, and models for farside occupants so that countermeasures could be evaluated (Digges et al. 2009). The consortium also studied the risk of
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Fig. 3. Biomechanical responses of the 5th percentile Hybrid III dummy in the 24 km/h (15 mph) tests with and without a side airbag.
occupant-to-occupant interaction in side impacts (Newland et al. 2008). The importance of far-side occupant injury has led GM to introduce a front center airbag in the 2013 Enclave, Acadia, and Traverse. The center airbag deploys to the right of the driver for protection in far-side impacts. Countermeasures designed to prevent ejection may help reduce far-side injury, in particular basilar skull fractures. Contacts with nonvehicle interior components accounted for more than 39% of far-seated basilar skull fractures, indicating partial or complete ejection with head impacts outside the vehicle. B-pillar contact was also a source for basilar skull fracture in near-seated occupants. Alem et al. (1984) reported that basilar skull fractures are generally associated with large forces and short impact durations. Energy-absorbing features such as padding or side airbags covering the B-pillar area may be beneficial countermeasures because they distribute contact forces, decrease peak accelerations, and increase impact duration; however, there is a trade-off on the stiffness of the airbag that would be needed to prevent basilar skull fracture for a far-side occupant and the safety of nearside adults and children, where out-of-position concerns exist (Hallman et al. 2009; McGwin et al. 2004; Yoganandan et al. 2007). The results of this study highlight the need for additional research on far-side occupant protection. Although the combo thorax–head side airbag was not beneficial, other types of airbags and padding may reduce injury risks. Certainly, seat belt use is effective in protecting far-side occupants but other countermeasure may be needed (Viano and Parenteau 2010).
due to basilar skull fracture, they do not cover the many other conditions where far-side occupants experience injury. The focus here was on a specific crash and injury. The results are specific to the test condition but do offer some insights about diving into a side airbag or curtain. The test setup involved the dummy prepositioned on the right side and placed 12 away from the side interior. The sled acceleration was over before the head impact. The initial conditions were selected to ensure matched tests where the influence of the side airbag was the focus. The testing did not involve the dynamics of a real-world crash, which may include pitch, yaw, and complex vehicle motion. The dummy was fully instrumented but the upper neck compression forces exceed the limit of the transducer, so the actual peak was not determined in the 32 km/h tests. The buck was built from a production vehicle and the body structure was reinforced to tolerate the sled acceleration. Finally, the tests did not simulate intrusion, which occurs in many farside impacts with serious injury. In some real-world crashes, the far-side occupant interacts with the intrusion, increasing the risks of injury.
Limitations
Alem NM, Nusholtz GS, Melvin JW. Superior–Inferior Head Impact Tolerance Levels. Ann Arbor, MI: University of Michigan Transportation Research Institute; 1982. UMTRI Report UM-82-42, Contract No. 210-78-0028.
With a limited test series, there are a number of limitations. Though the tests address a real-world crash with fatal injury
Supplemental Material Supplemental data for this article can be accessed on the publisher’s website
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Viano et al. Hallman JJ, Yoganandan N, Pintar FA. Characterization of torso side airbag aggressivity. Biomed Sci Instrum. 2009;45:101–106. Horsch JD. Occupant Dynamics as a Function of Impact Angle and Belt Restraint. Warrendale, PA: Society of Automotive Engineers; 1980:417–438. SAE 801310. Horsch JD, Schneider DC, Kroell CK. Response of Belt Restrained Subjects in Simulated Lateral Impact. Warrendale, PA: Society of Automotive Engineers; 1979. SAE 791005. Kahane CJ. An Evaluation of Side Impact Protection FMVSS 214 TTI(d) Improvements and Side Airbags. Washington, DC: NHTSA, DOT; 2007. DOT HS 810 748. Mackay GM, Parkin S, Hill J, Munns JA. Restrained occupants on the non-struck side in lateral collisions. In: Proceedings of the 35th AAAM Conference. Barrington, IL: AAAM; 1991:119–132. McCartt AT, Kyrychenko SY. Efficacy of side airbags in reducing driver deaths in driver-side car and SUV collisions. Traffic Inj Prev. 2007;8(2):162–170. McElhaney JH, Hopper RH Jr, Nightingale RW, Myers BS. Mechanisms of basilar skull fracture. J Neurotrauma. 1995;12:669–678. McElhaney J, Snyder RG, States JD, Gabrielsen MA. Biomechanical Analysis of Swimming Pool Injuries in the Neck—Anatomy, Injury Mechanisms and Biomechanics. Warrendale PA, Society of Automotive Engineers; 1979. SAE 790137. McGwin G, Metzger J, Loring W. The influence of side airbags on the risk of head and thoracic injury after motor vehicle collisions. J Trauma. 2004;56:512–517. Mertz HJ, Irwin AL, Prasad P. Biomechanical and scaling bases for frontal and side impact injury assessment reference values. Stapp Car Crash J. 2003;47:155–188. Moffatt EA. Occupant motion in rollover collisions. In: AAAM Proceedings. Barrington, IL: AAAM; 1975:49–59. Moffatt EA, Cooper ER, Croteau JJ, Parenteau C, Toglia A. Head excursion of seat belted cadaver, volunteer and Hybrid III ATD in a dynamic/static rollover fixture. SAE 973347. Warrendale, PA: Society of Automotive Engineers; 1997. Moffatt EA, James MB. Headroom, Roof Crush, and Belted Excursion in Rollovers. Warrendale, PA: Society of Automotive Engineers; 2005. SAE 2005-01-0942. Molz FJ, Bidez MW, Zeidler F, Breitner R. Spinal Burst or Compression Fractures Within Automotive Crashes Due to Vertical Force Components. Warrendale, PA: Society of Automotive Engineers; 1997. SAE 970498. Myers BS, Nightingale R. Review: the dynamics of near vertex head impact and its role in injury prevention and the complex clinical presentation of basicranial and cervical spine injury. J Crash Prev Inj Control. 1999;1:67–82. Newland C, Belcher T, Bostrom O, et al. Occupant-to-occupant interaction and impact injury risk in side impact crashes. Stapp Car Crash J. 2008;52:327–347. Nightingale RW, McElhaney JH, Richardson WJ, Best TM, Myers BS. Experimental impact injury to the cervical spine: relating motion of the head and the mechanism of injury. J Bone Joint Surg Am. 1996;78:412–421. Orlowski KF, Bundorf RT, Moffat EA. Rollover Crash Tests—The Influence of Roof Strength on Injury Mechanics. Warrendale, PA: Society of Automotive Engineers; 1985. SAE 85173. Parenteau CS, Viano DC. Basilar Skull Fractures by Crash Type and Injury Source. Warrendale PA: Society of Automotive Engineers; 2011. SAE 2011-01-1126. Pintar FA, Sances A, Yoganandan N, et al. Biodynamics of the total human cadaveric cervical spine. Paper presented at: 34th Stapp Car Crash Conference; 1990. Pintar FA, Yoganandan N, Voo L, Cusick JF, Maiman DJ, Sances A. Dynamic characteristics of the human cervical spine. Paper presented at: 39th Stapp Car Crash Conference; 1995. SAE J1733. Sign Convention for Vehicle Crash Testing. Warrendale, PA: Society of Automotive Engineers; 1994.
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SAE J211-1. Instrumentation for Impact Test - Part 1: Electronic Instrumentation. Warrendale, PA: Society of Automotive Engineers; 2003. Sances A, Yoganandan N, Maiman D, et al. Spinal injuries with vertical impact. In: Sances A, Thomas D, et al., eds. Mechanisms of Head and Spine Trauma. Goshen, NY: Aloray Publishers; 1986:717–736. Stolinski R, Grzebieta R, Fildes B, et al. Response of far-side occupants in car-to-car impacts with standard and modified restraint systems using Hybrid III and US-SID. SAE 1999-01-1321. Warrendale, PA: Society of Automotive Engineers; 1999. Viano DC. Biomechanics of brain injury. In: Nathan D, Zasler MD, Douglas I, Katz MD, Ross D, Zafonte DO, eds. Brain Injury Medicine. 2nd ed. New York, NY: Demos Medical; 2012:124–136. Viano DC, Casson IR, Pellman EJ. Concussion in professional football: biomechanics of the struck player—part 14. Neurosurgery. 2007;61:313–328.
733 Viano DC, Parenteau CS. Analysis of head impacts causing neck compression injury. Traffic Inj Prev. 2008;9(2):144–152. Viano DC, Parenteau CS. Severe injury to near- and far-seated occupants in side impacts by crash severity and belt use. Traffic Inj Prev. 2010;11:69–78. Viano DC, Pellman EJ. Concussion in professional football: biomechanics of the striking player—part 8. Neurosurgery. 2005;56:266– 280. Yoganandan N, Pintar FA, Zhang J, Gennarelli TA. Lateral impact injuries with side airbag deployments—a descriptive study. Accid Anal Prev. 2007;39:22–27. Zhang H, Ma D, Raman SV. CAE-Based Side Curtain Airbag Design. Warrendale, PA: Society of Automotive Engineers; 2004. SAE 200401-0841.
Traffic Injury Prevention Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gcpi20
Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant a
b
a
David C. Viano , Roger Burnett & Chantal S. Parenteau a
ProBiomechanics LLC, Bloomfield Hills, Michigan
b
Ford Motor Company, World Headquarters, Dearborn, Michigan Accepted author version posted online: 16 Jan 2014.Published online: 12 Jun 2014.
Click for updates To cite this article: David C. Viano, Roger Burnett & Chantal S. Parenteau (2014) Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant, Traffic Injury Prevention, 15:7, 726-733, DOI: 10.1080/15389588.2013.879124 To link to this article: http://dx.doi.org/10.1080/15389588.2013.879124
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Traffic Injury Prevention (2014) 15, 726–733 C Taylor & Francis Group, LLC Copyright ISSN: 1538-9588 print / 1538-957X online DOI: 10.1080/15389588.2013.879124
Influence of a Combo Side Airbag on the Risk for Basilar Skull Fracture in a Far-Side Occupant DAVID C. VIANO1, ROGER BURNETT2, and CHANTAL S. PARENTEAU1 1
ProBiomechanics LLC, Bloomfield Hills, Michigan Ford Motor Company, World Headquarters, Dearborn, Michigan
2
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Received 25 September 2013, Accepted 23 December 2013
Objective: The impact force to the head and neck were measured in sled tests with and without inflation of a combo airbag for a far-side occupant to determine the risk for basilar skull fracture. Methods: Sled tests were run at 24 and 32 km/h (15 and 20 mph) with and without inflation of a combo side airbag to analyze the effect of cross-car diving into the side interior. The matched tests involved one pair at 24 km/h and another at 32 km/h. The 24 km/h pair involved a lap–shoulder-belted 5th percentile female Hybrid III and the series at 32 km/h involved an unbelted 5th percentile Hybrid III. The dummy was ballasted to 69.5 kg (153 lb) and laid on the right side. The dummy was positioned 30.5 cm (12) from the far-side interior to ensure the full sled delta V occurred before head impact. The buck consisted of a 2001 Ford Taurus. The combo thorax–head side airbag was stored in the seatback. The airbag was triggered about 120 ms before the head impact. The head, chest, and pelvis were instrumented with triaxial accelerometers and the upper and lower neck, thoracic spine, and lumbar spine had transducers measuring triaxial loads and moments. High-speed video recorded different views of the dummy motion. Dummy kinematics and biomechanical responses were compared to study the influence of inflating the side airbag on the head and neck. Results: The top of the head impacted the far side. The force of impact was similar with and without the airbag as the head compressed the airbag and loaded the vehicle interior trim behind the airbag. The peak force on the head was primarily from neck load as torso augmentation occurred. For the 24 km/h (15 mph) tests, the peak force was 4.7 kN (1055 lb) without and 4.8 kN (1088 lb) with the airbag and there was over 2.67 kN (600 lb) of lap belt load. The peak head acceleration was 93 g without and 72 g with the airbag. For the 32 km/h (20 mph) tests, the force on the head was 15.3 kN (3433 lb) without and 15.2 kN (3406 lb) with the airbag, although the instrumentation saturated. The peak head acceleration was 236 g without and 262 g with the airbag. Conclusion: The airbag reduced head acceleration in the belted test but did not influence the diving forces from torso augmentation through the neck of the far-side occupant. The side airbag did not reduce the risk for basilar skull fracture due to high neck compression loads in either the belted or unbelted tests. Keywords: side impact, head injury, torso augmentation, basilar skull fracture
Introduction Far-Side Occupant Injury In a side impact, the vehicle is accelerated laterally by the collision. The side interior may be pushed inward depending on the severity of the crash and shape and stiffness of the impacting vehicle. The occupants will move laterally relative to the vehicle interior depending on the pulse and direction of force. The motion is influenced by forces from the interior or other occupants. For example, if the occupant’s lower body interacts with Associate Editor Clay Gabler oversaw the review of this article. Address correspondence to David C. Viano, ProBiomechanics LLC, 265 Warrington Rd., Bloomfield Hills, MI 48304-2952. Email: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gcpi.
the center console, the upper body may bend sideways. For farside occupants, contact is initially made with the center console or restraint system, followed by the occupant leaning and stretching toward the far-side interior (Gabler, Digges, et al. 2005; Moffat and James 2005; Douglas et al. 2007). Far-side occupants have more interior space to travel before contacting the far-side interior than near-side occupants. This allows more energy to be absorbed by the restraint systems, but movement in the interior can increase the speed of the occupants head when it contacts the far-side interior. The greater the distance the far-side occupant can travel, the more time there is for the vehicle to rotate and move relative to the occupant. As a result, the influence of the vehicle’s motion and intrusion differs between far-side and near-side occupants. Other factors influence occupant kinematics such as the belt fit and geometry. For the far-side belted occupant, the upper torso may slide out of the shoulder belt and strike the adjacent occupant or intruding structures.
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Impact Force to the Head With Side Airbag Far-side occupants account for 30% of injuries in real-world side impact crashes (Fildes et al. 2000). Fildes et al. (1994) carried out an in-depth study and showed that the frequency of Abbreviated Injury Scale 3+ head injury was greater in far-side than near-side impacts. Head injury was the most common injury type in far-side occupants (Fildes et al. 2007). Horsch et al. (1979) and Horsch (1980) documented occupant excursion in far-side impacts. Postmortem human subjects and dummies were in 35 km/h (21.7 mph) and 10 g sled tests with a lap and lap–shoulder belt in near- and far-side sled tests. The far-side occupant’s upper torso moved laterally and rotated about the restrained pelvis toward the adjacent seat. Table 1 summarizes some of the far-side occupant excursions in the literature. The lateral excursion was about 64–69 cm (25–27) in 24–31 km/h (15–17 mph) delta V far-side impacts. The time is approximately how long it took to reach the far side. Peak belt loads are listed.
Side Airbags Side airbags are primarily designed to protect near-side occupants in side impacts. There are thorax or torso-only airbags, torso–head airbags (combination airbags), and separate torso and head airbags such as an inflatable tubular structure or roof rail curtains. Side airbags are evolving with longer inflation times with coated airbags for rollover protection and to reduce ejection risks. Side airbags are effective in reducing side-impact fatalities for near-side occupants. McCartt and Kyrychenko (2007) reported a 37% reduction for head airbags and 26% reduction for torso-only airbags. Braver and Kyrychenko (2004) reported a 45% reduction for head–torso combination airbags and an 11% reduction for torso-only airbags. These results address near-side occupant fatality reductions with side airbags and include changes in the vehicle side structures to lower the velocity of side intrusion and provide space for the inflating airbags. Kahane (2007) found that torso and head airbags reduced fatality risks by 24% for near-side occupants. He also assessed the effectiveness of side airbags for far-side occupants and reported no fatality reduction with the torso–head combination side airbag for far-side occupants. The requirements for side airbag sensing are more stringent than for frontal airbags because of the reduced space between the occupant and the striking object in side impacts, the limited side interior space and structures, and the shorter detection and inflation times. Zhang et al. (2004) reported that side impact sensing needs to discriminate a crash condition warranting inflation within 6–13 ms compared to 15–25 ms for frontal impact sensing. Airbag inflation times for side impact airbags range from 20–30 ms compared to 45 ms for frontal airbags. Bostrom et al. (2008) discussed measures to improve the protection of occupants in far-side impacts. They demonstrated the effect of a coated side curtain in a 50 km/h (31 mph) delta V side impact. At 50 ms, the postmortem subject was supported by the high center console and belt system, but the force of the impact caused the upper body to rotate toward the far-side interior. Intrusion was simulated by mov-
727 ing the interior closer to the center of the vehicle to represent deformation from an Insurance Institute for Highway Safety high-hooded barrier impact. The far-side interior was located 60 cm (23.6) from the occupant’s head. Head contact with the inflated curtain occurred at about 100 ms. In this test, the position of the head was relatively high, since the occupant leans across the passenger seat and is somewhat upright. The head loaded the curtain above the beltline in the area of the side window. With less intrusion, the occupant leans more toward the far-side, stretches, and dives into the side interior below the beltline. As the occupant’s head contacts the far-side interior, inertial forces on the neck increase by torso augmentation. As the occupant dives into the far-side interior, the head stops but the torso keeps moving toward the head.
Torso Augmentation (Diving Injuries) The effect of torso augmentation on neck loading is well documented in the literature. Moffatt (1975), Orlowski et al. (1985), Bahling et al. (1990, 1995), and Moffatt et al. (1997) discussed the occupant diving into the roof during rollovers with the vehicle inverted. During an inverted drop, the head contacts the roof and stops while the torso continues to move downward. This causes a “diving” mechanism of neck loading on the basilar skull (McElhaney et al. 1979; Pintar et al. 1990, 1995). The neck is loaded from the head impact force and torso inertia. Spine or head injuries can occur depending on the vertebral strength and location, torso mass, and impact of force (Nightingale et al. 1996; Pintar et al. 1995; Viano and Parenteau 2008). Torso augmentation can also occur as the body moves downward with an underbody impact to a vehicle causing lumbar compression and burst fracture (Molz et al. 1997).
Basilar Skull Fractures McElhaney et al. (1995) investigated a series of drop tests with cadavers exposed to cranial loading. They reported that basilar skull fractures result when the head is “constrained on the impact surface and the inertia of the torso drives the vertebral column on the occiput” (p. 669, abstract). These findings are consistent with prior research showing that basilar fracture can occur with or without upper cervical injuries due to impacts on the top of the head oriented down the axis of the neck, where the inertia of the torso leads to neck compression forces (Alem et al. 1984; Myers and Nightingale 1999; Sances et al. 1986). Head impacts combined with inertia loading by the torso can lead to head or neck injuries in rollover and other crashes (Bambach et al. 2013) and spearing tackles in football (Bartsch et al. 2012; Viano 2012; Viano et al. 2007; Viano and Pellman 2005). The injury occurs in the cervical spine, base of the skull, or both depending on a number of factors. Parenteau and Viano (2011) assessed the risk of basilar skull fracture by crash type. They reported that basilar skull fractures more often occurred in rollovers and in side impacts. The most common contact source was the roof, side rails, and header in rollovers and the B-pillar in side impacts. The
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Table 1. Summary of far-side dummy excursion tests Excursion Max (cm) 64 (head) 47 (neck base) 61 (neck base) 69 (head)
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aS
Time (ms)
Barrier
Delta V estimate (km/h)
Belt load (N)a
Reference
140
ECE R95
31 35 35 24
S: 1202 L: 2799 S: 6822 S: 3600
Stolinski et al. (1999) Horsch (1980) with bucket seat Horsch (1980) with bench seat, timing from Horsch et al. (1979) Bostrom et al. (2003)
120 125
= shoulder, L = lap.
authors highlighted the benefit of seat belts. Compared to belted occupants, the relative risk is 9.0 times higher for unbelted, near-seated occupants and 16.3 times higher for farseated occupants. Basilar skull fractures are sometimes associated with large forces and short impact durations (Alem et al. 1984). Alem et al. (1982) carried out 10 kg (22 lb) impact tests on the crown of 14 cadaveric heads at 7 to 11 m/s (15.7–24.6 mph). A basilar skull fracture was observed at 15 kN (3372 lb) with 3 ms duration and 0.5 cm padding at 9 m/s (20 mph). They compared their findings to an earlier test (79H200) where a basilar skull fracture occurred after a 12 m/s (26.8 mph) impact with 2.5 cm (1)-thick pad. The results suggest that padding, particularly thick padding provided by a side airbag, may not lower the risk of basilar skull fractures in vehicle crashes. The objective of this study was to determine the effect of side airbag deployment on head and neck biomechanical responses using matched side impact tests with and without side airbag deployment.
Methodology Sled Buck and Setup Four sled tests were conducted at the Ford Safety Center in Dearborn, Michigan, with 2001 Ford Taurus bucks. The 2 unbelted tests at 32 km/h (20 mph, H32534 and H32534) were run on February 12–13, 2013. Two belted tests at 24 km/h (15 mph, H32555 and H32556) were run with another 2001 Taurus buck on March 1–2, 2013. The same setup was used for each series with a 5th percentile female Hybrid III dummy (Backaitis and Mertz 1994) ballasted to 69.5 kg (153 lb) lying on her right side on the driver’s seat. The sled test is representative of a side impact to the rear door and wheel area that does not deform the B-pillar but causes high delta V . The study was motivated by a real-world case of this type where we were interested in whether the side airbag could have helped prevent a fatal basilar skull fracture with head impact on the side interior below the beltline. Though intrusion is a factor in many far-side collisions, there will be some impacts where the occupant compartment remains intact and the far-side occupant stretches toward the side interior with a head impact on the door trim or B-pillar. The Taurus was aligned at 108◦ on the sled to simulate a side impact at less than 4 o’clock principal direction of force. Appendix 1 (see online supplement) shows the pretest setup. The dummy was placed on the right side on a low-
friction sheet of Teflon with 0.3 cm (0.125) thickness resting on a 15.2 cm (6) thickness of dense foam. This allowed the dummy to move toward the far-side interior. The height of foam aligned the head impact with the B-pillar trim below the beltline. It approximated the height of the armrest or center console as the occupant leaned toward the far-side interior. The setup positioned the head in line with the B-pillar below the beltline on the far side and centered on the inflated combo side airbag (head and chest airbag) deployed from the seat. The dummy was place 30.5 cm (12) away from the interior so the full delta V from the sled acceleration occurred before contact on the far side. The side airbag was triggered before the sled acceleration to approximate a head contact at about 120 ms, consistent with the time for a driver to reach the farside in a severe side impact. The B-pillar was undeformed and did not simulate intrusion that can occur with side impacts on the doors. The top of the dummy’s head was painted to determine contacts during the test. The sled tests involved a short-duration pulse to ensure that the full delta V occurred before head contact on the far side. The 32 km/h (20 mph) tests involved 41 g peak sled acceleration. The 24 km/h (15 mph) tests involved 20 g peak sled acceleration. High-speed cameras photographed occupant kinematics and the head impact on the far side. The 5th percentile female Hybrid III dummy was instrumented with an array of transducers to measure head triaxial acceleration, upper and lower neck moments and forces, thoracic spine moments and forces, lumbar spine moments and forces, and triaxial chest and pelvic acceleration. The triaxial accelerometers at the head center of gravity were used to determine peak resultant head acceleration, HIC15 and HIC36 . The spinal transducers measured upper and lower neck responses and lower thorax and lumbar responses. The 6-axis load cells measure axial tension–compression, lateral and fore–aft shear forces, and flexion–extension, lateral and rotation moments. Lap belt load was measured in the two 24 km/h (15 mph) tests. The belt load was measured at the outboard lower anchor.
Instrumentation and Filtering Sled acceleration (Endevco 7264B-500) was measured according to the SAE J211-1 and filtered to channel frequency class (CFC) 60 (Society of Automotive Engineers [SAE] 2003). The delta V was determined by integration of the sled acceleration using CFC 180. The maximum time for data collection was 300 ms. The Hybrid III dummy data were recorded according
Impact Force to the Head With Side Airbag
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to SAE J211-1 (SAE 2003). Filtering was done on the dummy responses with CFC 1000 for head, CFC 180 for spine acceleration, CFC 1000 for neck force, and CFC 600 for neck moments. Upper neck moments were corrected with the neck force to report occipital condyle moments in accordance with SAE J1733 (SAE 1994). Impact Force
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Impact force (F) in the z direction was determined for the head. The diving motion of the dummy was into the far-side interior and involved forces down the axis of the neck and spine. Impact force in the z direction (Fz ) involved the head acceleration in the z direction (az ) and the upper neck force in the z direction (FNz ): Fz = mhead az + FNz ,
(1)
where mhead is 3.68 kg (8.1 lb) and includes the mass of the Hybrid III head (3.34 kg) and the mass of the upper neck load cell above the sensing element (0.34 kg). The combo head–thorax side airbag used in these tests was an option for the 2001 Ford Taurus. The side airbag was developed for the regulated 53.9 km/h (33.5 mph), 27◦ crabbed movable FMVSS 214 barrier and for the 50 km/h (31 mph)km/h deformable 90◦ ECE R95 barrier impacts on the front door. The side airbag was designed for near-side occupant protection.
Results Figure 1 shows side-by-side images from the high-speed video of tests H32555 (left images with no airbag) and H32556 (right images with airbag) at nominally 24 km/h (15 mph) delta V with a belted dummy. Test setup photos can be seen in Figure A1 (see online supplement). In these tests, the sled was triggered at 55 ms and acceleration was over at 110 ms. The side airbag was remotely triggered at 25 ms. The airbag can be seen starting to deploy out of the seat at 25 ms and it is fully inflated at 58 ms. The dummy contacts the airbag at about 124 ms and deforms it into the B-pillar with a spike in head acceleration at 148 ms. The impact causes the neck to compress as the torso moves toward the far-side. Without the airbag, the dummy rebounds toward the driver seat, away from the principal direction of force. With the airbag, the head is pushed forward toward the instrument panel causing neck flexion. Figure 2 shows the force on the head in the z direction. The dotted line is with the airbag and involves an earlier loading of the head, although the peak force is nominally the same. The peak force was 4.7 kN (1055 lb) without and 4.8 kN (1088 lb) with the airbag. With the airbag inflated before the sled acceleration, the dummy’s head contacted the airbag and compressed it into the side interior trim. This did not influence the neck compression force. There was more than 2.7 kN (600 lb) of lap belt load. The complete set of peak responses is provided in Table A1 (see online supplement). The peak occupant biomechanical responses were normalized to
Fig. 1. (a) Side-by-side images of the side airbag inflation and occupant impact on the far side in sled tests H32555 (left, no airbag) and H32556 (right, with airbag). (b) Side-by-side images of the side airbag inflation and occupant impact on the far side in sled tests H32555 (left, no airbag) and H32556 (right, with airbag). (Continued)
the 5th percentile dummy injury assessment reference value (IARV) provided in Mertz et al. (2003). For comparison, the 32 km/h (20 mph) tests had a peak force on the head of 15.3 kN (3433 lb) without and 15.2 kN (3406 lb) with the airbag in the z direction, although the instrumentation in the upper neck saturated, so the actual load was higher. Figure 3 shows other biomechanical responses from the 24 km/h (15 mph) tests with a belted dummy. The resultant head acceleration shows the head impact on the B-pillar. It is lower with the airbag and occurred earlier. The peak resultant acceleration was 93 g without the airbag and 72 g with the airbag. The upper neck compression shows about the same level of peak load. The resultant chest acceleration was 29.7 g without the airbag and 30.7 g with the airbag. The upper neck flexion moment is higher with the airbag as the head is deflected forward, causing more neck flexion than with the airbag.
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Fig. 2. Head impact force (Fz ) in the 24 km/h (15 mph) tests with and without a side airbag.
Fig. 1. (Continued)
Several peak responses are above IARV for the 5th percentile female dummy. The upper neck compression force was 214% of IARV with the side airbag and 207% without the airbag in the 24 km/h (15 mph) tests with a belted occupant. The upper neck flexion was 189% with the airbag and 108% without the airbag. The upper neck compression force was 531% of IARV with the side airbag and 531% without at 32 km/h (20 mph) tests with the unbelted dummy. Figure A2 (see online supplement) shows posttest photos with chalk transfer associated with head impact on the far-side B-pillar in test H32555. The chalk transfer can be seen on the airbag in Figure A3 (see online supplement) with test H32556. In the right photo, the airbag has been pulled up to show the chalk transfer to the center of the side airbag.
Discussion The matched tests show that the side airbag does not reduce upper-neck compression forces at the base of the skull, even
when the dummy was lap–shoulder belted and there was over 2.7 kN (600 lb) of belt restraining load. The review of the test video highlighted the “torso augmentation” mechanism that occurred in the far-side impact. The occupant dives toward the side interior with the torso augmenting the loading of the neck at the base of the skull. This mechanism of injury to the basilar skull or neck has been well documented in motor vehicle crashes and sports. The compression forces in the upper neck load cell were 5.3 times tolerance in the 32 km/h sled tests and over 2.0 times in the 24 km/h tests (Table A1). The actual peak load in the unbelted test was not determined as the load cell saturated. Both series showed a high risk for injury due to neck compression based on human tolerances (Mertz et al. 2003). In the 24 km/h tests, the side airbag reduced the peak head acceleration; however, in the higher velocity tests, the airbag was not sufficient to dampen the head acceleration as the head quickly compressed the airbag and loaded the side interior. In both series, the head rebounded off the side interior while the torso was still diving toward the interior. In the lower speed tests, the airbag caused the head to displace forward, flexing the neck and allowing head contact on the instrument panel. Without the airbag, the head rebounded off the side interior. The full dummy tests show that the inflation of a far-side combo airbag does not alter the risk for basilar skull fracture. The tests also show that the airbag can redirect the head forward and cause neck flexion. Though the peak head acceleration is lowered somewhat with the airbag in the belted test, the forces at the base of the neck are not influenced and the airbag can increase neck flexion and lateral bending. There is currently no regulation to assess far-side occupants in side impacts. Research groups have been working on far-side occupant protection because of the involvement in serious-to-fatal injury (Digges and Dalmotas 2001; Digges and Gabler 2006; Digges et al. 2005; Fildes et al. 2000; Frampton et al. 1998; Mackay et al. 1991). In 2004, an international consortium was formed to assess far-side occupant kinematics and injury (Fildes et al. 2005; Gabler, Fitzharris, et al. 2005). The objective of the consortium was to develop representative test conditions, injury criteria, and models for farside occupants so that countermeasures could be evaluated (Digges et al. 2009). The consortium also studied the risk of
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Fig. 3. Biomechanical responses of the 5th percentile Hybrid III dummy in the 24 km/h (15 mph) tests with and without a side airbag.
occupant-to-occupant interaction in side impacts (Newland et al. 2008). The importance of far-side occupant injury has led GM to introduce a front center airbag in the 2013 Enclave, Acadia, and Traverse. The center airbag deploys to the right of the driver for protection in far-side impacts. Countermeasures designed to prevent ejection may help reduce far-side injury, in particular basilar skull fractures. Contacts with nonvehicle interior components accounted for more than 39% of far-seated basilar skull fractures, indicating partial or complete ejection with head impacts outside the vehicle. B-pillar contact was also a source for basilar skull fracture in near-seated occupants. Alem et al. (1984) reported that basilar skull fractures are generally associated with large forces and short impact durations. Energy-absorbing features such as padding or side airbags covering the B-pillar area may be beneficial countermeasures because they distribute contact forces, decrease peak accelerations, and increase impact duration; however, there is a trade-off on the stiffness of the airbag that would be needed to prevent basilar skull fracture for a far-side occupant and the safety of nearside adults and children, where out-of-position concerns exist (Hallman et al. 2009; McGwin et al. 2004; Yoganandan et al. 2007). The results of this study highlight the need for additional research on far-side occupant protection. Although the combo thorax–head side airbag was not beneficial, other types of airbags and padding may reduce injury risks. Certainly, seat belt use is effective in protecting far-side occupants but other countermeasure may be needed (Viano and Parenteau 2010).
due to basilar skull fracture, they do not cover the many other conditions where far-side occupants experience injury. The focus here was on a specific crash and injury. The results are specific to the test condition but do offer some insights about diving into a side airbag or curtain. The test setup involved the dummy prepositioned on the right side and placed 12 away from the side interior. The sled acceleration was over before the head impact. The initial conditions were selected to ensure matched tests where the influence of the side airbag was the focus. The testing did not involve the dynamics of a real-world crash, which may include pitch, yaw, and complex vehicle motion. The dummy was fully instrumented but the upper neck compression forces exceed the limit of the transducer, so the actual peak was not determined in the 32 km/h tests. The buck was built from a production vehicle and the body structure was reinforced to tolerate the sled acceleration. Finally, the tests did not simulate intrusion, which occurs in many farside impacts with serious injury. In some real-world crashes, the far-side occupant interacts with the intrusion, increasing the risks of injury.
Limitations
Alem NM, Nusholtz GS, Melvin JW. Superior–Inferior Head Impact Tolerance Levels. Ann Arbor, MI: University of Michigan Transportation Research Institute; 1982. UMTRI Report UM-82-42, Contract No. 210-78-0028.
With a limited test series, there are a number of limitations. Though the tests address a real-world crash with fatal injury
Supplemental Material Supplemental data for this article can be accessed on the publisher’s website
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