Investigation into the noise associated with airbag deployment: part III - sound pressure level and auditory risk as a function of inflatable device.

Several criteria for assessing noise-induced hearing loss from automotive inflatable devices, such as airbags, were proposed in the past. However, their development was based on epidemiological studies of steady state noise and not impulsive noise. More recently, the US Army Research Laboratory (ARL) developed and validated a mathematical model of the ear, which may be used to assess noise induced hearing loss from impulsive noise sources. Previous studies have contributed to understanding the effects of impulse noise on occupants, but were performed on first generation frontal airbags and did not provide information on airbag and occupant safety systems in today's fleet of vehicles. This study presents the results of a parametric investigation of current inflatable devices across a variety of vehicles and considers the size and seating location of the occupant in vehicles of varying volume. In addition, the study considers advanced airbag technologies such as dual stage frontal airbags, side airbags, inflatable curtains, and seat belt pretensioners.

Lower extremity injuries in lateral impact: a retrospective study.

ABSTRACT A retrospective analysis of the NASS/CDS database from 1993 to 2000 was used to investigate lower extremity injury in lateral impact. The analysis includes the study of the injury patterns, crash characteristics and the interactions between the occupant and the vehicle interior, including injuries to the farside occupants. The findings include significantly different injury patterns for the nearside and farside impacts. In particular, while the proportion of pelvis/hip injuries, with respect to AIS2 and AIS3 lower extremity skeletal injuries and 2-4 and 10-8 o'clock side impacts, was higher in nearside (70.4%) than farside (38.3%), the opposite trend was observed for the thigh (2.8% vs 4.5%), knee (6.2% vs 16.7%), leg (10.1% vs 19.5%) and foot/ankle (5.6% vs 14.7) injuries. Analysis of the PDOF suggested that a large proportion the impacts occurred obliquely, at approximately 10 and 2 o'clock, with a rearward component of force. It is hoped that the findings of the current study can help to investigate injury mechanisms.

Rate of blunt impact loading affects changes in retropatellar cartilage and underlying bone in the rabbit patella.

Our laboratory has developed a small animal model using Giant Flemish rabbits to examine chronic degradative changes in joint tissues following a blunt impact. Historically, we observe surface fissuring and decreases in the elastic modulus of retropatellar cartilage along with thickening of the underlying subchondral bone. Previous studies resulted in load insults that peaked in approximately 5ms, while loads that occur during automotive accidents or heavy exercise can produce longer rise times. The objective of the current study was to examine the influence of blunt impact loading rate using our established model. We hypothesized that the extent of fissuring and softening of retropatellar cartilage following impact would not be significantly different for a high (5ms to peak) versus low (50ms to peak) rate of loading experiment. Eight animals were impacted with a high rate of loading blunt impact, while ten animals were subjected to the same impact load at a low rate of loading. An additional eight animals served as a control population. All animals were sacrificed 12 months post-impact. The study yielded unexpected results for the first hypothesis. The high rate of loading experiments generated more surface fissuring of the retropatellar cartilage than the low rate of loading experiments. However, the degree of softening was similar for the two rates, which supported the second hypothesis. Furthermore, the study documented more thickening of bone underlying retropatellar cartilage following the high versus the low rate of loading experiments. The current study suggested that chronic injury mechanisms may be highly dependent on the rate of impact loading. These data could become extremely relevant in the development of high-velocity "safety" devices, such as knee air bags, that are needed to help position an unbelted occupant in an automobile crash.

The effect of loading rate on the degree of acute injury and chronic conditions in the knee after blunt impact.

accidents are often overlooked, but can have a profound societal cost. Knee injuries, for example, account for approximately 10% of the total injuries. Fracture of the knee is not only an acute issue but may also have chronic, or long term, consequences. The criterion currently used for evaluation of knee injuries in new automobiles, however, is based on experimental impact data from the 70's using seated human cadavers. These studies involved various padded and rigid impact interfaces that slightly alter the duration of contact. Based on these data and a simple mathematical model of the femur, it appears fracture tolerance increases as contact duration shortens. In contrast, more recent studies have shown mitigation of gross fractures of the knee itself using padded interfaces. The use of padded interfaces, however, result in coincidental changes in contact duration and knee contact area. Therefore, it is difficult to extract the direct effect of loading rate on fracture tolerance of the knee. The object of the current study was to isolate the effect of loading rate alone on fracture tolerance of the human knee joint. Paired experiments were conducted on eight pairs of isolated cadaver knees impacted with a rigid interface to approximately 5 kN at a high (5 ms to peak) or low (50 ms to peak) rate of loading. Gross fracture and occult microfractures of the knee joint were documented. A second part of the study examined some chronic effects of loading rate on "subfracture" injuries in an animal. Thirty-four rabbits were subjected to a "subfracture" knee load at the same rates as used in the human studies. Alterations in the mechanical properties of retropatellar cartilage and thickening of subchondral bone were documented out to one year post "subfracture" trauma to the joint. The current study documented an opposite effect than that expected based on 70's experiments with seated cadavers. There was an increase in the number of gross fractures and occult microfractures in high versus low rate of loading experiments. A similar effect was also seen in the "subfracture" chronic animal experiments, which showed relatively more degradative change in the mechanical properties of cartilage following high versus low rate of loading experiments. There was also a significant increase in subchondral bone thickening underlying cartilage and increased fissuring of cartilage in high versus low rate of loading experiments. The current study suggests a relative decrease in tolerance of the knee at high versus low rates of loading in acute experiments with human cadavers and in the chronic setting with animals. Therefore, it would appear that rate of knee loading may be an important issue in establishing a future injury criterion for the knee itself.