National Academies Press: OpenBook

Developing Improved Civil Aircraft Arresting Systems (2009)

Chapter: Appendix E - Human Injury Study

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Page 181
Suggested Citation:"Appendix E - Human Injury Study." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 181
Page 182
Suggested Citation:"Appendix E - Human Injury Study." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 182
Page 183
Suggested Citation:"Appendix E - Human Injury Study." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 183

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181 A previous study (31) investigating the effectiveness of arresting systems for civil aircraft suggested a deceleration limit of 1 g for this type of analysis but provided no reference for this design requirement. To establish a design require- ment for the airplane with a medical basis, literature from the development of ejection seats, high-g maneuvers, and air- plane crash reconstructions were reviewed. From this review, human injuries were related to the deceleration of the fixture volunteers were riding. This appendix is a summary of the lit- erature review. It provides insight into the human tolerance to deceleration for a wide range of durations and suggests deceleration limits for the evaluation of arrestor systems. E.1. Range of Human Tolerance to Deceleration To obtain an evaluation criterion based on human toler- ance levels, reports from ejection seat tests, airplane deceler- ation tests, and aeronautical accident reconstructions were reviewed. The range of decelerations reviewed was from 2 g to 220 g, with durations from 0.002 seconds up to 115 sec- onds. This encompasses the range of decelerations within which aircraft arrestor systems will most likely stop an air- plane. From the literature reviewed, this deceleration range has been broken down, based on the duration of the deceler- ation pulse, into three broad categories as shown in Table E-1: (1) less than 0.2 seconds, (2) 0.2 to 3 seconds and (3) greater than 3 seconds (45). Each category is also graphically repre- sented in Figure E-1 to illustrate the trends in the data. The following sections describe in more detail the types of injuries observed within each category. E.1.1. Deceleration Durations Less Than 0.2 Seconds For decelerations less than 0.2 seconds (200 ms) in dura- tion (Figure E-1 – Region 1) and when the body is sufficiently restrained (i.e., the body does not come in contact with any objects inside the cabin), the risk of injuries has been attrib- uted to the rapid displacement of body fluids. The rate of displacement, and therefore the human tolerance to the deceleration forces, is primarily determined by the rate of application of force acting on the fluids. The rate of applica- tion of force is the third derivative of motion, called “Jerk,” with the units of g-per-second (g/sec). The literature docu- ments that, in this category, the point of reversible incapaci- tation is 38 g when the rate of application is 1350 g/sec and increases to 50 g when the rate of application is reduced to 500 g/sec or less (46). Reversible incapacitation is defined as momentary lack of awareness of an individual that can limit their ability to extricate themselves from the airplane if necessary. These symptoms can range from disorientation to blackout and last for just a few seconds to several days. The lower bound for these effects begins within the human body at 10 g (45). In addition to the displacement of body fluids, injuries can be also induced by the interaction of the body with the restraining device or the motion of unrestrained body regions such as the head and limbs. These injuries are similar to those observed in automotive crashes. These injuries include bruis- ing (46, 47), muscle strains, muscle tears, concussions (mild traumatic brain injuries) (45), and fractures when the body impacts the seatbelt with force (48) or strikes an object inside the cabin. In an exercise examining the injury threshold for the occurrence of traumatic brain injuries (TBI) based on idealized deceleration curves, the results suggested that injuries to the brain can be induced by deceleration starting at 10 g for impact durations of 0.2 sec. These findings are based on the response of the average male occupant. The response can vary slightly based on the gender and age of the occupant. This difference is illustrated by the upper and lower bounds in addition to age and gender. Simple items such as foam pads on the back of the seat can also significantly change the peak deceleration and the impact duration (49); there- A P P E N D I X E Human Injury Study

fore, great care should be exercised when using an aircraft deceleration of 10 g as an injury criterion by itself. In a review of aircraft accidents, Moseley (50) observed that although the aircraft’s deceleration was within human tolerance limits (<10 g), injuries were still sustained. In the Moseley report, many of the injuries sustained were due to unrestrained body regions striking objects in front of them (50). One possible reason for the higher rate of injury, as reported by the Committee for Aeronautics, is that the accel- erations measured in the instrumented Anthropomorphic Test Device’s (ATD) chest were 1.2 to 1.5 times the peak acceleration measured at the floor (48). Therefore, a sled deceleration of 40 g approaches the injury threshold for the chest as specified by the 3 ms clip criterion. The 3 ms clip cri- terion is an automotive injury criterion that specifies that an acceleration of the chest greater than 60 g can cause serious injuries (51). 182 R egion 1 R egion 2 R egion 3 Figure E-1. Decelerations with documented human response. Decel (g) Ave t (sec) Reported Injury Cited 220 0.060 Lethal in Anesthetized Hogs (45) 125 0.060 Reversible Injury in Anesthetized Hogs (45) 70 0.130 Lung Injury in Chimp Similar to Blast Lung (45) 50 0.200 Reversible Loss of Consciousness (500 g/sec) (45) 45 0.050 Concussion (45) 38 0.200 Reversible Loss of Consciousness (1350 g/sec) (45),(55),(56) 26 0.002 Back Muscle Soreness (47) 18 0.100 Upper Limit Head and Limb Motion Can be Braked by Musculature (57) 17 0.300 Sudden Pressure to the Epigastrium and Rib Margin (55) 16 0.090 FAA Std for Peak Floor Deceleration (52) 15 — Suggested Human Tolerance Limit (57) 14 >0.200 Lumbar Fx if Max Torso Flexion is Attained (45) 13 >0.200 Abdominal Strain (47) 12 >0.200 Where Seat Belt Rides Up (46) 10 0.002 Bruising (46), (47) 10 0.200 Hydrostatic Pressure Effects Begin (45),(56) 9 — FAA Std for Seat Decal Limit (52) 8 0.310 Neck Muscle Soreness (46) 8 60.0 150% Loss in Respiratory Capacity (57) 6 3.0 Pilot Can Still Maneuver Plane (58) 6 60.0 15% Loss in Respiratory Capacity (57) 4 2.0 Eye and Sinus Hemorrhages (46) 4 80.0 Dimming of Vision (59) 2 115.0 Flatting of T-Wave (Serious Arrhythmia) (59) Table E-1. Summary of the human response to deceleration from the literature reviewed.

For emergency crash landings for which the deceleration duration is typically very short, the FAA has set standards for airplane safety. The FAA standard stipulates that the peak floor deceleration of the plane must not exceed 16 g, or have a rate of application (jerk) greater than 178 g/sec (52). The structures within the aircraft must be able to withstand the forces generated by this deceleration pulse for at least 3 sec- onds. From this deceleration pulse, the standard also requires that the peak deceleration experienced by the occupant must not exceed 9 g (52). E.1.2. Deceleration Durations from 0.2 to 3 Seconds If the duration of the deceleration pulse is lengthened to between 0.2 and 3 seconds (Figure E-1 – Region 2), a greater transfer of energy to the fluid systems of the body can be expected (46). In this range, injuries reported for rapid dis- placement of body fluids at 10 g now begin at 4 g due to the longer deceleration duration (45). In this interval, the heart and circulatory system has time to react, and is working at maximum output to counteract the effects of the decelera- tion. This increased cardiac output, in some individuals tested, led to an irregular, rapid, and inefficient heartbeat (tachycardia) (53). If not corrected, extreme tachycardia cases can be life threatening (54). In addition to circulatory problems, the deceleration forces can force fluids to pool in body regions, exceeding the elasticity of tissues and causing blood vessel rupturing (45). These injuries can be observed as ruptures of the blood vessels in the eyes and skin. In the eval- uation of pilots’ responses it was determined that pilots still had the cognitive facilities to control the plane if exposed to accelerations of 6 g for up to 3 seconds. We hypothesize that passengers of an aircraft could extricate themselves from the cabin after a similar experience. E.1.3. Deceleration Durations Greater Than 3 Seconds When the duration of the deceleration exposure is 3 sec- onds or greater (Figure E-1 – Region 3), the observed injuries are primarily determined by the hypoxic effects (45). The hypoxia is caused by a combination of poor blood circulation and poor respiratory output. Since the deceleration occurs over a period of time up to 120 seconds, the onset of symp- toms will be more gradual. The initially reported symptom is dimming of vision (53), then loss of breath, dizziness and ultimately, for long duration deceleration, loss of conscious- ness (55). The injury threshold for these long duration decel- eration pulses is between 2 and 8 g. E.2. Injury-Based Criteria for Evaluating Arrestor Systems To define the human tolerance to deceleration and suggest a human tolerance limit for use in the analysis of existing and future arresting systems, literature was reviewed and an exer- cise examining the injury threshold for the occurrence of TBI was undertaken. The results of the literature review indicate that a single injury criterion is not applicable for the full range of deceleration durations anticipated in the evaluation of the arresting systems. Therefore, a three-tiered deceleration limit for the evaluation is proposed (Figure E-1). The first is for decelerations with durations under one second, the second for decelerations with durations between one and three seconds, and the third for deceleration durations over three seconds. For deceleration durations less than 1 second, the data reviewed indicates that 9 g is a reasonable limit. For this tier, the risk of incapacitation or injury due to rapid displacement of body fluids is minimized. In addition to a lower risk of incapac- itation, there is a reduced risk of bodily injury. For these short decelerations below 9 g, the airplane cabin will remain intact and is within the design limit for the seat anchors. By remain- ing within the design limits of the airplane structure, the poten- tial of injury from the body striking objects inside the cabin is reduced. If the head comes into contact with the structures inside the cabin, the potential for injury is estimated to be low. For the analysis of airplane deceleration between one and three seconds, the peak acceptable deceleration must be reduced to 6 g. By limiting the peak deceleration to 6 g, the lit- erature suggests that the forces placed on the body by the longer deceleration will not affect the passengers’ cognitive ability to extricate themselves from the cabin. When the duration of the deceleration exposure is 3 seconds or greater, it is proposed that the criterion be further reduced to 4 g. The reduction should minimize the occurrence of reported symptoms such as dimming of vision, loss of breath, dizziness, and ultimately, for long duration deceleration, loss of consciousness. All these symptoms could contribute to the passenger’s ability to exit the airplane after an incident. The results of this effort indicate that a tiered approach is required for the analysis of airplane arresting systems. For deceleration durations less than 1 second, the proposed injury threshold is 9 g to reduce the risk of incapacitation or injury due to rapid displacement of body fluids and head impacts to interior structures within the cabin, respectively. For the analy- sis of airplane deceleration between one and three seconds, the peak acceptable deceleration proposed is 6 g. When the dura- tion of the deceleration exposure is 3 seconds or greater, it is proposed the criterion be further reduced to 4 g. By maintain- ing the deceleration to these limits, passengers should have the physical and cognitive ability to safely exit the plane. 183

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TRB’s Airport Cooperative Research Program (ACRP) Report 29: Developing Improved Civil Aircraft Arresting Systems explores alternative materials that could be used for an engineered material arresting system (EMAS), as well as potential active arrestor designs for civil aircraft applications. The report examines cellular glass foam, aggregate foam, engineered aggregate, and a main-gear engagement active arrestor system.

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