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Importance of Lethal Traumatic Asphyxia from Crowd Crush

What is Compressive Asphyxia?

Compressive asphyxia refers to a mechanical restriction of respiration, typically from an external pressure applied to one's body[1]. In the context of this chapter, focus is directed to acute, dynamic cases of traumatic compressive asphyxia in the thoracic region as a result of hyperactive crowds [1].

The mechanism of a lethal case of traumatic asphyxia is physical pressure on the thorax which restricts respiratory movements of the chest and venous return to the head [1]. During panic, individuals also experience deep breathing and glottal closure, which significantly increases central venous pressure. In a situation where arterial pressure is maintained but venous flow is reversed, this causes capillary rupture and subsequently hemorrhaging in the upper body [1]. Compounding this with being physically compressed between 2 or more barriers, the physical prevention of chest expansion consequently limits the respiratory tidal volume which sends a person into a hypoxic state, thus causing death after an extended period of time [1]. Biomechanical studies report that rib fracture occurs at 3000 N, and death can occur at 6227 N applied for 15 seconds, or 1112 N for 4-6 minutes [2]. The severity of these metrics is realized by the fact that only 6-7 people pushing in one direction to produce forces of 4500 N [2]. Additionally, individuals lose their ability to resist compression from 162 N for young women, to 242 N for middle aged men [2].

Epidemiology of Traumatic Asphyxia in Crowd Crush

The most common environments where crowd crush occur are concerts, sporting matches, schools, protests, and places of worship or religious gatherings [3]. As one might observe, most of these environments are "indoors" or involve some sort of physical obstacle. In scenarios indoors or involving obstacles (ex. staircases, slippery hills, etc), more opportunity arises for individuals to lose balance and/or get trapped against. The most common causes of panic in a crowd involve a threat, natural disasters/bad weather, exceeding a venue's capacity, police dispersion/de-escalation, or a combination of several of these. Mainly, this involves any scenario where a group is trying to move towards one exit point at once.

Regions where crowd crush are most common are in Southern Asia, Africa, and South America [4]. Some things that these regions have in common are the large population densities, the lower-middle income status, frequency of large religious gatherings, and popularity of attending heated soccer matches [3]. The demographic most at risk are weaker individuals with less ability to defend themselves from external pressures, thus being the children, seniors, and women [3]. However, it is important to consider that this doesn’t mean that they are the most represented in the fatalities. Adult men, for example, are probably most likely to attend soccer matches, especially in some of these south-east Asian and African countries where women are less likely or entirely not permitted to attend similar events, for religious reasons.

Statistics of Lethal Crowd Crush Incidents

It is important to note that quantifying the difference between lethal and non-lethal scenarios of traumatic asphyxia is difficult because deaths are more reported and easier to keep track of as opposed to injuries [3][5]. Several sources agree that the most common mechanism of traumatic asphyxia is by experiencing forces from several directions thus suspending them in a vertical position, as opposed to a popular suspecting of being trampled [3][5]. Scenarios where a crowd is moving in one single direction is reportedly associated with a fatality risk of 3.5 times that of multiple directions. This is suggested to be from the compounding effect of forces in this one direction [3]. Many crowd crush incidences range from 5-50 deaths, however there are several instances where it can reach several hundred or even thousands of deaths [4]. Some examples of severe cases include 300 deaths in an Ethiopian political protest perpetuated from crowd dispersion methods, a religious pilgrimage in Saudi Arabia where overcrowding resulted in 300 deaths, or an Indonesian soccer game where riots and panic caused 135 deaths [4]. Looking from 1980-2012, approximately 350 stampede events occurred where 10,243 deaths and 22,445 injuries were incurred [3]. One incident stands out, and emphasizes the relevance of crowd crush after the COVID-19 pandemic, which is the Seoul Halloween crowd crush incident. This event claimed 160 lives, reporting an average applied force of 1063 N/m and peak forces of 1961 N/m, from the 38 000 individuals engaging in bidirectional collisions, with panic and urgency [6].

Relevance of Asphyxia in Crowd Crush

Indeed, this is still a relevant topic of biomechanics that should continue to be focused on as even from 2006-2016 there were over 4000 deaths and 6300 injuries among 100 crowd crush accidents [4]. This is especially relevant because in dynamic conditions, forces can increase from 300 N to 1400 N even with small contact velocities of 0.2-1.2m/s, compared to static conditions [2]. Considering this, it is important to recall that death from compressive asphyxia can occur after 15 seconds with a force of 6227 N, or after 4-6 minutes with 1112 N [2]. The FIST model, explained in one biomechanical paper emphasizes how horizontal forces that are dynamic from individuals pushing each other are going to be representative in compressive asphyxia cases [2]. Knowing this, this emphasizes how lethal dynamic conditions can be, and how prevalent these incidents of crowd crush still are, especially in lower middle income countries that have high attendance events.

Current Research

Validated Models for Compressive Asphyxia Research

With the population growing globally, and full return to packed venues and large crowds post pandemic, compressive asphyxiation has become an increasingly prevalent problem. Considering this, a number of papers in the literature have attempted to design experiments and analyses around the physics, biomechanics, and injury risk of what is coined traumatic asphyxia. Although this literature review aims to discuss the injury biomechanics and implications of traumatic asphyxia relating to crowd density and compression, research studies considering alternate traumatic asphyxiation scenarios will be summarized as they present critical findings on risk of injury and limits of the human thorax under pressure.

The methodology used in literature for the study of compressive thoracic forces varies depending on the application of the study, however a few broad trends can be recognized. Due to ethical concerns and risk of injury, injurious testing on human subjects does not exist. However, use of Finite Element Models (FEMs), Anthropometric Test Dummies (ATDs), adapted training instrumented mannequins, and animal models are all validated surrogates within this field of experimentation.

Factors Affecting Deflection of the Thoracic Cage

Figure 1: Average displacement of chest corresponding to distributed loading up to 60kg on instrumented CPR training. (Adapted from data collected in the referenced paper[7])
Figure 2: (a) The chest deflection in 50th percentile male dummy as a function of vehicle speed. The average static deflection obtained during the prolonged contact of the vehicle on the chest after the impact was plotted at zero speed. (b) The chest deflection in 5th percentile female dummy as a function of vehicle speed. The average static deflection obtained during the prolonged contact of the vehicle on the chest after the impact was plotted at zero. (Adapted from data collected in the referenced paper[8])

The main focus of traumatic asphyxia research lies in determining the factors of loading that affect deflection of the thoracic cage and the subsequent effects on respiration. Studies such as those conducted by Ikuta et al., and Sances et al. apply loading at the front of the thorax, with a rigid barrier behind it (i.e. floor, wall)[7][8]. This set up aids in furthering the understanding of the relationship between compressive thoracic cage movement, vital lung capacity, and injury risk. Results from these experiments show that in a supine position, past a weight of 30kg, vital lung capacity decreases, thus initiating an asphyxiating scenario[7]. This is directly related to a decrease in the anteroposterior thoracic diameter causing a rotational downward shift in the rib cage and consequently restricting ideal movement of the diaphragm, contributing to a decrease in lung capacity[7]. Refer to Figure 1 for the correlation between loading and average displacement. Similarly demonstrated in animal studies, a frontal thoracic load of more than three times body weight subjected the animal model to risk of death, and loading more than five times body weight caused asphyxiation after a short duration[7]. In a seated position against a wall, frontal loading greater than 1956N (5th percentile female) and 2438N (50th percentile male) was determined to cause injurious deflection in the thorax when tested on ATDs[8]. These conclusive results determine that high, quasi static forces applied to the chest have the potential to be extremely injurious[8]. Refer to Figure 2 for the range of chest deflection measured in the ATDs.

One paper in particular analyzes the effects of orientation of the thorax and the angle of incidence of the force to predict risk of injury to the lungs[9]. Results show that the duration of pressure peak is significantly higher during frontal impacts compared to impacts to the side of the thoracic region[9]. The evidence from this study suggests that frontal impacts pose a high risk of death, with only a 10-50% chance of survival, while side impacts may have up to a 90% chance of survival[9]. It is important to note however, that this particular application was considering blast waves, which subject the model to very high forces over a very short period of time. Although this may be compared to being stepped on or trampled in a crowd crush setting, it is not likely that these forces will reach the magnitudes of a blast wave. The key takeaway of this study is the evidence on how orientation of the thorax contributes to injury risk of the lungs. An incidence angle of 0 degrees (frontal) is much more likely to cause asphyxia than at an angle of +/-90 degrees (side) [9].

Loads Causing Thoracic Damage

Figure 3: Visualization of the force applied onto the thoracic region, investigated by Kroll et al. (Image adapted from [10])

A paper by Kroll et al. used a thoracic model to determine the forces required to cause flail chest, the fracture of six ribs, as defined in their methodology[11]. Results show that a static load of 2550 ± 250 N caused fractures in six ribs, while a dynamic load of 4050 ± 320 N was required to have the same effect [11]. In both cases, it was found that the sternum does not experience high loads given that the force is spread over a large surface area and dispersed into the ribs [11]. However, it is discussed that this model is not sufficient to model crowd crush scenarios, and that the cause of fatalities in those scenarios is typically compressive asphyxia rather than flail chest [11]. Nonetheless, this experiment helps deepen understanding of how the thorax reacts to distributed loads. Another study by Murakami et al. compared a thoracic FE model to post-mortem human surrogates to delve into force-deflection behaviours from different belt loaders [12]. Three different tissue types were evaluated (intact, denuded, and eviscerated), and it was found that stiffness plays a key role in how the thorax responds in different loading scenarios, especially with the eviscerated model [12]. The intact model had greater stiffness in all loading scenarios than the human surrogate, whereas the denuded and eviscerated models matched the human surrogate stiffness within the error corridor [12]. In both the models and the human surrogates, the distributed loading scenario resulted in the greatest posterior forces at 20% chest deflection [12]. The authors discussed the importance of including accurate tissue properties in models to allow for useful experimental results [12].

While it is unethical to subject human volunteers to injurious forces, one study explored the contact forces due to various levels of overcrowding by asking volunteers to walk at varying speeds while in a small (40 cm radius) enclosed space [2]. Pressure sensors on the middle volunteer found that contact force increases as crowding levels increase, with forces reaching up to 500N [2]. It was mentioned in the study that it would require 242 N for a middle-aged male to lose the ability to resist in a crowd and 600 N for a super fit young male adult to lose this ability [2]. Overall, this study found that experienced forces increase as velocity increases, emphasizing the danger of unstable crowds [2]. While the forces experienced by the individuals in this study were not injurious, data from the experiment can still be used to gain a deeper understanding of human tolerances to these types of forces.

Problems & Controversies

To date, most of the research surrounding compressive asphyxia as a result of crowding has focused on analyses of past fatalities and assumptions of the conditions under which victims found themselves. The uncertainty behind the magnitude and duration of loading applied to the victim’s thorax has left gaps in the literature, specifically in connecting contributing factors and resulting outcomes.

Assumptions of Factors Influencing Compressive Asphyxia

One key reason for the abundance of assumptions made by researchers is the wide range of variable factors that may influence the dynamics of compressive asphyxia and the resulting fatalities. The vast majority of papers assume that a load applied on the chest eventually restricts one’s total lung capacity, leading to asphyxia and eventual death. However, Motomura et al. proved the significant risks of abdominal compression, in addition to thoracic, due to the restriction of the diaphragm’s motion[13]. By limiting the downward motion of the diaphragm, the lungs do not attain the negative pressure required to inspire air, inhibiting ventilation, and thereby respiration.

In addition to this, current papers analyze the point at which an individual can no longer attain an adequate total lung capacity, and name this “compressive asphyxia”[11][2]. However, it has been proven that prolonged shortness of breath, which is survivable for short periods of time, also contributes to eventual asphyxia[13].

Another variable surrounds the position of the victim, and the orientation of the thorax being compressed, or the direction of loading. The majority of studies simulate supine anterior-posterior loading, likely assuming that victims are positioned in this orientation[13][11][2][12][7][9][8]. Despite anterior-posterior compression producing the most significant pressure on the lungs, the effects of loading on a rotated or upright thorax do present additional considerations[7].

Finally, crowd dynamics present a number of additional variables including total space occupied and crowd motion. Previous studies have used crowd density - number of people per unit area - as a measure of occupied space, however, this metric does not account for the size of the people within that space. A more accurate metric is defined as the space occupancy rate, accounting for the area of the space, the number of people and the body area of each person[2].

To overcome some of the other variables and properly detect the presence of compressive asphyxia, some studies use markers that they deem indicative of the injury. Namely, rib fractures, facial petechiae, subconjunctival hemorrhage, ecchymosis, or cervicofacial cyanosis[11][12]. However, as mentioned, intermittent or extended periods of thoracic or thoracoabdominal loading may not produce acute mechanical injuries, but do contribute to compressive asphyxia[13]. Markers such as these are therefore not representative of several cases.

Challenges Surrounding Study Subject Identification & Utilization

In terms of experimental subjects, previous research has primarily studied living humans, other animal models and computer models. While cadavers and Anthropometric Test Devices (ATD) are useful for measuring chest deflection in response to a load, they are not sufficient for measuring the physiological response of this compression, which requires functioning lungs. Each of the aforementioned models feature inherent limitations. Firstly, living humans may not be subjected to injurious loads for ethical reasons, or properly instrumented with load cells to measure the exact force applied[13]. As a result, estimated sub-injurious loads are usually applied and results are extrapolated to determine the effects of higher forces[13]. Post-experimental analyses also sometimes model ribs as beams and rigid structures to simplify the complex biomechanics of the thorax[11]. This simplification does overlook several physiological factors raising doubts about the accuracy and relevance of the results from these studies. Amplifying this issue is that existing quantitative data and experiments on human thoracic compression thresholds primarily focus on high-velocity impacts, such as those seen in car crashes, rather than the low-velocity, high-force events typical of compressive asphyxia in crowd injuries[11]. In animal models, anaesthesia is usually employed to keep the subject in a given position, mimicking a person pinned in a crowd injury[13]. However, anaesthesia disrupts normal breathing patterns, rendering results inapplicable to general injuries[13]. Finally, computer models are based on results obtained from human experiments. However, as previously mentioned, these results are usually estimates, and computers are unable to perfectly simulate the physiological complexities of the human lungs.

Controversies in Compressive Asphyxia Research

Several social factors and controversies contribute to the lack of adequate research papers on this topic. Firstly, as with any fatal injury, compressive asphyxia is a sensitive subject to approach with research, specifically due to its history as a torture method[11]. One factor that compounds this difficulty is the epidemiology of this injury, mainly affecting children and the elderly, due to their smaller frame, weaker abdominal and thoracic muscles and flexible thorax[13]. Ethical requirements often limit the use of children or elderly individuals as subjects, as experimenting on such populations is generally frowned upon, and injuries to children are particularly upsetting events [14]. As a result, relevant sample sizes are quite small, and the findings may not be directly applicable to the vulnerable population or account for common degenerative diseases that may influence injury dynamics.

Further, a link has been drawn between instances of compressive crowd injuries and low and middle income countries (LMIC), with religious gatherings seeing the greatest number of crowd crush incidents and subsequent fatalities[15]. Not only is there limited funding and research opportunities in LMIC, but the intrusion of researchers into sacred gatherings complicates the access to data needed to determine outcomes of crowd crush injuries. Further, crowd injuries in these settings unfortunately produce several casualties, complicating autopsies and post mortem analyses due to the high volume required and low resource settings[13]. It is not uncommon for the dynamics of the injury and fatality to remain unanalyzed following crowd crush.

Another interesting factor is the state of individuals in these crowds. Veering away from religious gatherings and towards social ones, it is not unusual for crowd attendees to be inebriated, and similarly to anaesthesia, alcohol intoxication and overdose also affects respiratory patterns by slowing down the breathing rate[16]. Research has not yet been conducted on victims in this state, likely due to the ethics surrounding drunk participants.

The variables surrounding compressive asphyxia dynamics greatly complicate the experimental methods required to produce accurate and applicable results. As a result, previous studies tend to feature several assumptions and limitations. Controversies surrounding study subjects, post-mortem analyses and the use of substances add additional complexities by introducing social and ethical factors that must be considered. These challenges highlight the need for more comprehensive research surrounding compressive asphyxia.

Future Work

While there has been a wide variety of research conducted on traumatic asphyxia regarding crowd crush and its associated fatalities, there are still many aspects of the problem that have yet to be explored. The majority of the biomechanical experiments focus on anterior-posterior loading. While analyzing the mechanics of this loading orientation is important for investigating the most probable scenario of compressive asphyxia within a crowd, there is still a chance that individuals may be subject to similar loads from a more lateral angle of incidence. To meticulously model the loading that an individual faces in a crowd crush, it is suggested that future biomechanics studies focus on or including lateral loading scenarios. Combining the resulting data with existing anterior-posterior data would allow for improvement of computational thorax models. Additionally, the majority of research has designed experiments with artificial weights replicating point loading scenarios on the thorax. This is a simplified representation of the forces experienced in dense crowds, as forces are applied from various directions. Future experiments investigating the effects of multiple points of loading from varying angles could help further understand the biomechanics of compressive asphyxia.

Research has shown how breathing patterns can be affected when an individual is subjected to high thoracic forces, but there is a gap in which the experimentation does not account for possible breathing impairments incurred prior to an impactful incident. Drugs and alcohol are typically consumed at venues hosting large entertainment events where crowd density is high, facilitating crushing forces. Consequently, these substances are known to alter regular breathing patterns and may predispose individuals to a higher risk of injury via asphyxiation. As a depressant, alcohol and other select drugs slow down the user’s respiratory rate. In the event of crowd crush, inebriated individuals may be at an even greater risk of asphyxia due to this initial reduction of oxygen intake. Thus, it is suggested that future research design and validate computational thorax models with customizable breathing rates and patterns to investigate the effects of substance use related to traumatic asphyxia. Similarly, breathing rates and patterns may be affected by stress, which is inevitable in life threatening cases, as with crowd crush. Adapting computational models, as mentioned above, to analyze this rapid change in respiration, combined with current research on respiration changes associated with feelings of panic, may produce critical conclusions of injury risk in the context of traumatic asphyxia in crowds.

The mechanism of flail chest has been investigated in many experiments but is difficult to separate from the mechanism of compressive asphyxiation in crowds. The force required to cause asphyxiation is much less compared to that required to break an individual’s ribs. There is limited information regarding flail chest fatalities in crowd crushes, which could be an interesting topic for future case studies to help determine what biomechanical experiments should focus on. One study looks into how loading on the sternum results in flail chest[15], but it would be interesting to see if posterior loading on the thorax would have similar results. A study focusing on overcrowding looked into forces on the body from all directions[11]. A future study could employ similar methodology with ATDs instead of human subjects, allowing for implantable load cells and the use of injurious forces to visualize the effects of loading from multiple directions on the thorax.

Long-term static loading has been the focus for the majority of the research regarding crowd crush compressive asphyxia. However, crowds tend to be dynamic and their resulting forces as well. One study that looked into long-term static loading showed that it resulted in fatalities due to restricted breathing[15]. It would be interesting to investigate whether long-term dynamic loading leads to the same outcomes.

The thoracic models that have been made for biomechanical experiments, both computational and physical, feature bones of uniform composition. While this is ideal for generalizability and ease of use, it can lead to results that lack transferability. Human ribs have varying properties, such as a differing Young’s modulus (elasticity) amongst sections of the bone, causing unique reactions across the sections. Considering this, and the differences in bone properties throughout different age groups (child, adult, elderly), a possible fruitful suggestion may be to incorporate osteoporotic and cartilaginous bone into the models. These factors may allow research avenues and findings applicable to the elderly and adolescent populations, considering these demographics are at highest risk in a crowd crush scenario.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Tumram, Nilesh Keshav; Ambade, Vipul Namdeorao; Dixit, Pradeep Gangadhar (2014-06). [10.1097/PAF.0000000000000052 "Compression asphyxia in upright suspended position"] Check |url= value (help). The American Journal of Forensic Medicine and Pathology. 35: 80–82. Check date values in: |date= (help)
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 Li, Xudong; Song, Weiguo; Xu, Xuan; Zhang, Jun; Long, Xia; Shi, Congling (July 2020). "Experimental study on pedestrian contact force under different degrees of crowding". Safety Science. 127.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 UNDRR (June 7 2023). "Stampede or Crushing (Human) | UNDRR". United Nations Office for Disaster Risk Reduction. Retrieved March 10 2025. Check date values in: |access-date=, |date= (help)
  4. ↑ 4.0 4.1 4.2 4.3 "List of fatal crowd crushes". Wikipedia. February 25 2025. Retrieved February 25 2025. Check date values in: |access-date=, |date= (help)
  5. ↑ 5.0 5.1 Sun, Libo; Badler, Norman I. (2018-11-27). [10.3390/s18124149 "Exploring the Consequences of Crowd Compression Through Physics-Based Simulation"] Check |url= value (help). Sensors (Basel, Switzerland). 18: 4149.
  6. ↑ Liang, Haoyang; Lee, Seunghyeon; Sun, Jian; Wong, S.C (2024-7-12). [10.1371/journal.pone.0306764 "Unraveling the causes of the Seoul Halloween crowd-crush disaster"] Check |url= value (help). PLOS ONE. 19. Check date values in: |date= (help)
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Ikuta, E.; Miyano, M. (2010). "Study of Damage to the Human Body Caused by Earthquakes: Development of a Mannequin for Thoracic Compression Experiments and Cyber Mannequin Using the Finite Element Method". Human Casualties in Earthquakes. Springer. pp. 275–289. ISBN 978-90-481-9455-1.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Sances, A.; S., Kumaresan; F., Carlin (January 6, 2003). "Biomechanical study of traumatic asphyxia due to thoracic load". Proceedings of the Second Joint 24th Annual Conference and the Annual Fall Meeting of the Biomedical Engineering Society] [Engineering in Medicine and Biology]. 3: 2487–2488.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Roth, Sebastien (May 4, 2018). "Three-dimensional numerical study of the influence of the thorax positioning submitted to blast loading: Consequences on body trauma". Mechanics of Advanced Materials and Structures. 27: 396–402.
  10. ↑ Kudzinskas, Kudzinskas; Callahan, Avery L. (2023). "Anatomy, Thorax". StatPearls – via PubMed.
  11. ↑ 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 Kroll, Mark W; Still, G Keith; Neuman, Tom S; Graham, Michael A; Griffin, Lanny V (April 3, 2017). "Acute forces required for fatal compression asphyxia: A biomechanical model and historical comparisons". Medicine, Science and the Law. 57.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 Murakami, Daisuke; Kobayashi, Seiichi; Torigaki, Toshikazu; Kent, Richard (November 6, 2006). "Finite Element Analysis of Hard and Soft Tissue Contributions to Thoracic Response: Sensitivity Analysis of Fluctuations in Boundary Conditions". SAE. 50: 398–419.
  13. ↑ 13.00 13.01 13.02 13.03 13.04 13.05 13.06 13.07 13.08 13.09 Motomura, Tomokazu; Matsumoto, Hisashi; Yokota, Hiroyuki; Suzuki, Mototsugu; Nishimoto, Tetsuya; Ujihashi, Sadayuki (August 20, 2019). "Thoracoabdominal Compression Model of Traumatic Asphyxia to Identify Mechanisms of Respiratory Failure in Fatal Crowd Accidents". Journal of Nippon Medical School. 86: 310–321.
  14. ↑ Murphy, Thomas F. (August 2003). "The Ethics of Research with Children". AMA Journal of Ethics.
  15. ↑ 15.0 15.1 15.2 Faliciani, Claudio; Corbetta, Alessandro; Haghani, Milad; Nishinari, Katsuhiro (August 2023). "Trends in crowd accidents based on an analysis of press reports". Safety Science. 164.
  16. ↑ "Alcohol's Effects on Health". National Institute on Alcohol Abuse and Alcoholism. December 2024. Retrieved Mar. 9, 2025. Check date values in: |access-date= (help)


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