Prediction of injuries caused by explosive events: A case study of a hand incident in

T.N. WHYTE1, I.M. SNYMAN1 and B.L. MEEL2 1CSIR DPSS, Landwards Sciences, PO Box 395, Pretoria, 0001 Email: [email protected] 2 Walter Sisulu University for Technology and Science, Faculty of Health Sciences, Department of Forensic Medicine

Abstract explosive devices involved in which 16 children and 5 adults were killed (See Table 1). An M26 hand grenade was accidentally detonated by a group of eight children, six of whom were Type and number Date of Child Adult killed, in the Mthatha area of South Africa. The M26 of hand incident deaths deaths grenade is designed to produce casualties through involved the high velocity fragments that it expels. However, 03/01/1998 2 0 M26 (x 2) if one is close enough to the grenade primary blast 01/06/1998 6 0 M26 (x 1) injuries will occur in addition to penetration injuries caused by the fragments. Simulations were 28/12/1998 1 1 Unknown (x 1) conducted to obtain pressure profiles that could be 02/07/1999 3 0 M26 (x 1) produced by the explosive charge contained in the 28/11/2000 0 0 M26 (x 1) grenade. Injury predictions were then made, using 28/11/2000 0 0 RGD5 (x 2) currently available injury criteria and compared to 02/02/2001 1 1 M26 (x 1) one another and to the actual injuries that were sustained by the children. The validity of currently 12/11/2004 0 3 M26 (x 1) available pressure-based injury criteria to predict 13/04/2005 0 0 Unknown (x 1) injuries when the subject is in very close proximity 23/08/2006 2 0 M26 (x 1) to the explosive charge is still unknown. Further 18/07/2007 0 0 M26 (x 1) such case studies and research into injury 04/09/2007 1 0 M26 (x 1) mechanisms and injury criteria are necessary to enable injuries caused by explosive events to be accurately predicted. This will allow improved Table 1: Hand Grenade incidents in the Mthatha protection strategies against explosive events to be area of South Africa developed. The South African manufactured M26 hand 1. Introduction grenade was the most common threat in these incidents. There is evidence that a substantial In this case report, an M26 hand grenade number of small arms are unaccounted for containing high energy explosives was found and following apartheid era South Africa (Greenstein, unintentionally detonated by children who were 2003). With the integration of the Transkei Defence minding cattle. Eight children were involved. Six of Force into the South African National Defence them died instantly, and the other two sustained Force in 1994, 715 firearms were not accounted for minor injuries. These children were between 9 and (Greenstein, 2003). Presumably, in this process 16 years of age. The police said the device was an hand grenades were also unaccounted for. A M26 grenade of South African origin. Commission of Inquiry into politically-motivated violence, led by Judge Richard Goldstone, found that the Transkei government had supplied the Azanian People’s Liberation Army with arms. This Several hand grenade incidents have been finding could explain a portion of the unreturned reported in the Transkei area since 1998. Eleven firearms. It is hoped that this study will raise public such incidents were reported in the Daily Dispatch, awareness that people in South Africa are still Herald, South African Broadcasting Channel being killed by these explosive devices. (SABC) News, Mail & Guardian. There were 14

1 M26 hand grenades were designed to supplement small arms fire against enemy in close combat. They were designed to be thrown into the vicinity of enemy targets to produce casualties through the high-velocity projection of fragments (Hand Grenades, 2007). The grenade is 113 mm in length with a diameter of 60 mm (Denel: M26 HE Hand Grenade, 2007) and is filled with 160 g of high- energy Composition B1 charge. The total weight of the grenade is 465 g and it produces approximately 1000 small fragments weighing about 200 mg each (Denel: M26 HE Hand Grenade, 2007). The grenades can be identified by an olive drab body with a single yellow band at the top with yellow markings which are indicative of the high-explosive filler. A diagram of the M26 grenade can be seen in Figure 1 and a photograph of the grenade is shown in Figure 2.

Figure 2: Photograph of a M26 hand grenade (Denel: M26 HE Hand Grenade, 2007). A fragmentation grenade such as the M26 produces a complex set of injury mechanisms that produce injury to humans within certain ranges. Wounding mechanisms caused by explosive events can be categorised as follows (White, 1968) (Ripple and Phillips, 1997) (Cooper et. al., 1991):

• Primary blast injury (PBI) caused by the direct effects of the blast (blast induced

variations in the environmental pressure). Figure 1: Diagram of an M26 fragmentation This could result in injuries to the lungs, hand grenade (Hand Grenades, 2007). upper respiratory tract, gastrointestinal tract and solid intra-abdominal organs. 1 These injuries could occur when the victim Composition B consists of RDX (Cyclonite) and TNT (trinitrotoluene) in the ratio 60:40 (Köhler and Meyer, 1993). is in very close proximity to a grenade containing high-energy explosives. • Secondary ballistic injuries due to fragmentation and flying debris. This is the mechanism by which the M26 grenade is intended to cause injury. • Tertiary injuries are caused by whole body displacement. • Miscellaneous injuries such as burns and toxic fume inhalation. Burns could possibly be caused if the subject was in the fire-ball resulting from an explosive event.

2 Criteria have been developed which relate Personal Protective Equipment Against Anti- measurements that can be taken during explosive Personnel Mine Blast, 2004). events to possible injury severities caused by the wounding mechanisms described above. A case An alternative to the Bowen criterion (Bowen, study, as is presented in this paper, provides Fletcher and Richmond, 1968) is the CWVP researchers with an opportunity to gauge the (Axelsson and Yelverton, 1996) which takes into validity of criteria that have been developed to account the upper respiratory tract, gastrointestinal predict injuries. The M26 grenade is designed to tract and solid intra-abdominal organs, in addition inflict injury through high-velocity fragments under to the lungs which were also considered in (Bowen, normal operating conditions. In this case study, the Fletcher and Richmond, 1968). This criteria was children were handling the grenade directly at the developed to take into account complex blast time of detonation (which would not usually be the waves (as one might find if an explosive was to case as the grenade is designed to be thrown into detonate in an enclosed space or near reflecting the general vicinity of the enemy and relies on the surfaces), but it is also valid for the free field case. fragments inflicting injury over a 15 m radius). ests were conducted by exposing sheep to Thus, in addition to the fragments causing serious explosive events. The injuries were graded per injury, due to the close proximity of the children to body region using an alphanumeric scoring system the exploding device, primary blast injuries caused (Axelsson and Yelverton, 1996). by pressure effects may also be observed. In this study, a simulation of the M26 hand grenade It is well known that the higher the peak pressure, was performed and predicted pressures from the the more severe the injuries caused by this literature were obtained. By using these pressure pressure will be. It is also accepted that longer profiles at various distances from the grenade, positive phase pressure durations result in more injury criteria can be used to predict possible severe injuries than if the duration was shorter injuries at those positions. The mechanisms of (Cooper, 1996) (White, 1968) (Axelsson and injury resulting from the primary and secondary Yelverton, 1996) (Bowen, Fletcher and Richmond, effects of the explosive event, in relation to the 1968) (Richmond et. al, 1968) (Bouamoul, Williams distance of a victim to the grenade, will be and Levesque, 2007). discussed.

Two commonly used injury criteria for predicting 2. Incident Analysis injuries caused by pressure profiles arising from explosive events are the Bowen criterion (Bowen, 2.1 Incident description Fletcher and Richmond, 1968) and the Chest Wall Velocity Predictor (CWVP) (Axelsson and At autopsy, all children had their ventral aspects Yelverton, 1996). mutilated or greatly lacerated. A bluish green

substance was deposited over the abdomen and The Bowen criterion is used to predict injuries chest. The boy closest to the blast sustained caused by explosive events in a free field abdominal and chest mutilation, while those near environment (i.e. not in an enclosure or near him sustained deep lacerations to the torso. The objects which may cause complex reflected waves lungs and intestines were diffusely contused in to interact with the subject). This criterion requires three of the boys. The two boys who were a an incident overpressure and a duration considerable distance from the blast escaped with measurement. The criterion was derived from minor injuries. mortality studies conducted on mammals and risk curves were produced to predict human injuries for various peak overpressures and positive-phase 2.2 Simulation of the M26 hand grenade and durations of the blast wave (Yelverton, 1996). predicted pressures from literature sources Modifications to the Bowen criterion for short duration blasts were proposed by Bass et. al. 2006, ANSYS AUTODYN2D software was used to however, the original Bowen curves are currently calculate the pressure at three locations of a 160 g used for overpressure injury assessment in armour spherical TNT charge that approximates the M26 testing standards (e.g. Test Methodologies for hand grenade. The explosive and air are modelled with the Euler Gudonov solver in an axial

3 symmetric geometry. The air and explosive gas are 18000 allowed to escape across the boundaries. The ideal [Petes, 1968] predictions 16000 gas equation of state models the air and the 14000 [Swisdak, 1975] predictions explosive is modelled with the Jones-Wilkens-Lee 12000 (JWL) (Lee, Hornig and Kury, 1968) equation of ANSYS AUTODYN simulation state. In Figure 3 the overpressure time histories at 10000 locations 0.1 m, 0.2 m and 0.5 m are shown. The 8000 reflected pressure time histories at 0.2 m, 0.5 m 6000 4000 and 1.0 m are shown in Figure 4. (kPa) overpressure Peak 2000

0 16000 0.1 m 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 14000 Distance from 160g spherical TNT charge 0.2 m 12000 0.5 m 10000 Figure 5: Graph showing the predicted peak 8000 overpressure values at various distances from a 160 g TNT charge as by simulations and in 6000 the literature. Overpressure (kPa) Overpressure 4000

2000 70000 [Swisdak, 1975] predictions 0 60000 0.0 0.1 0.2 0.3 0.4 0.5 Time (ms) 50000 ANSYS AUTODYN simulation

40000

Figure 3: Graph showing simulated 30000 overpressure (side-on pressure) predictions at various distances from 160g spherical TNT 20000 charge. Peakreflected pressure (kPa) 10000

0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 50000 Distance from 160g spherical TNT charge

0.2 m 40000 0.5 m Figure 6: Graph showing the predicted peak

30000 1.0 m reflected pressure values at various distances from a 160 g TNT charge as by simulations and

20000 in the literature. The computation of the peak reflected pressure at

Reflected pressure (kPa) pressure Reflected 10000 the various locations by ANSYS AUTODYN and the formula from (Swisdak, 1975) are shown in 0 Figure 6. 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Time (ms) The overpressure at a location is the effect of the shock pulse without any obstruction, that is, the Figure 4: Graph showing simulated reflected pressure wave passes without any interference pressure predictions at various distances from across the location. This pressure is also known as 160g spherical TNT charge. side-on pressure. The reflected pressure is the Peak pressure values were obtained from various effect at the location when the pressure wave is formulae based on experiments (e.g. (Petes, obstructed by a surface so that the pressure wave 1968), (Swisdak, 1975), (Swisdak, 1999) and has to change its flow, that is, the pressure wave is (Kinney and Graham, 1985)). Peak pressure reflected back towards its origin. The peak values from the literature together with the reflected pressure is between 2 and 8 times the computational results are shown in Figure 5. peak overpressure (according to (Swisdak, 1975)).

4 Both these values therefore give an indication of 50 the effect of a blast on an object or a person. 0.2 m 40 0.5 m 30 Although the M26 grenade is designed to cause 1.0 m injury through the projection of high-velocity 20 fragments, due to the close proximity of the 10 0 children to the grenade, the primary effects (such 0.00 0.50 1.00 1.50 2.00 as blast overpressure) may result in more severe -10 injuries than would be expected due to the wall (m/s)Chest velocity -20 fragments alone. -30 -40 From the peaks and durations of these pressure Time (ms) curves, injury criteria can be used to predict possible injuries that could occur at certain distances from the charge. Figure 7: Graph showing the simulated Chest Wall Velocity Predictions for the pressure 2.3 Injury predictions using pressure based profiles recorded at various distances from injury criteria 160g spherical TNT charge.

The simulated peak overpressure and positive- At a distance of less than or equal to 0.5 m the phase durations shown in Figure 3 can be used to injury severity was moderate to extensive and predict primary injuries at various distances from corresponded to a greater than 50% chance of the grenade. Unfortunately the positive-phase lethality (Axelsson and Yelverton, 1996) At a durations used in (Bowen, Fletcher and Richmond, distance of 1 m the severity decreases to trace to 1968) only go down to 0.2 ms and the durations slight or slight to moderate (Axelsson and shown in Figure 3 for distances less than 0.5 m Yelverton, 1996). from the grenade fall below 0.2 ms. However, at

0.5 m from the grenade the positive-phase duration Although the M26 hand grenade has been is approximately 0.3 ms. The peak overpressure at predicted to cause serious injury using the this distance is approximately 1507 kPa which is pressure profile criteria outlined above, as above the threshold for lung damage but below the mentioned before, the grenade is primarily 99% chance of survival curve (as deduced from the designed to produce injury via high velocity curves indicated in (Bowen, Fletcher and fragments. In the simulation conducted to predict Richmond, 1968) for a 70kg man applicable to a the pressure profiles at various distances from the free field situation where the long axis of the body grenade, the velocities of the fragments were also is perpendicular to the blast winds. measured. From 0.01 ms it was found that the

fragments already achieved peak velocities in Although it is unclear if the CWVP criterion is valid excess of 1400 m/s which was maintained until at for positive-phase durations of less than 0.4 ms, as least 0.3 ms, at which stage they are approximately tests were not conducted for that loading rate, 0.5 m from the original centre of the grenade. The MatlabTM simulations using this criterion were fragments cause damage by transferring kinetic conducted. This was achieved though the use of energy to the body tissue which causes the tissue the pressure profiles obtained from the simulations to be damaged (Zajtchuk, 1990). These high shown in Figure 4. The results are shown in Figure velocity fragments result in the grenade having a 7. 50% casualty radius of 15 m, however the fragments are able to disperse out to 230 m (Denel: M26 HE Hand Grenade, 2007).

Injuries in very close proximity to the grenade would be more severe due to the dramatic increase in peak pressure values as the distance to the grenade decreases. However, this is speculation and further work needs to be conducted to

5 understand the injury mechanisms when the body They were within the 50% casualty range due to is exposed to excessive peak pressures with very the fragments produced by the grenade. short positive-phase durations, for which the currently used pressure based injury criteria may 2.3.2 Children in the outer circle: not be valid. Four children may have crouched over the inner Figure 8 shows the regions within which injuries two and could have been within 0.3 m to 0.5 m of due to primary and secondary injuries caused by a the grenade. At 0.5 m all of the children could have M26 hand grenade may be expected. The grenade exceeded the threshold for lung damage, however is positioned in the centre of the diagram. The they would have a less than 1% chance of lethality orange circles indicate limits described for various due to the primary effects of the explosive event levels of injury severity due to primary effects and alone (Using the Bowen criterion (Bowen, Fletcher the black circles indicate areas in which injuries and Richmond, 1968)). Using the CWVP criterion caused by fragments could occur. (Axelsson and Yelverton, 1996), at 0.5 m the children would have a 50% chance of lethality due to the primary injuries which they sustained. They were all within the 50% casualty range due to the fragments produced by the grenade.

2.3.3 Children witnessing the event:

The two children who witnessed the event were outside the range of injury due to the primary effects of the blast, but the minor injuries which they sustained may have been due to the fragments which dispersed.

3. Discussion of explosive event injury criteria and research applications

Figure 8: Diagram showing the regions within It can be concluded that the injuries described in which primary and secondary injuries caused the autopsy reports correlate well with the by a M26 hand grenade may be expected. predictions made surrounding the primary and secondary effects of the explosion.

By speculating the proximity of the children to the This study focussed on predicting primary injuries grenade, one can correlate the injuries described in caused by the explosive charge, which, although it the autopsy reports with the predictions made is understood that the fragments are the intended surrounding the primary and secondary effects of injury mechanism of the M26 hand grenade, the explosion. provide insight into the use of current pressure based injury criteria to predict injuries in very close 2.3.1 Children in the inner circle: proximity to explosive charges.

The child holding the grenade could have been It was found that the Bowen criterion (Bowen, within 0.2 m of the grenade and another child could Fletcher and Richmond, 1968) predicted less have been within 0.3 m of the grenade. Both severe injuries within a meter of the explosive children in the inner circle could thus have charge than the CWVP criterion. The differences in exceeded the threshold for lung damage (Using the severity are highlighted in Table 2. Bowen criterion (Bowen, Fletcher and Richmond, 1968)) due to the primary effects of the explosive event. Using the CWVP criterion (Axelsson and Yelverton, 1996), within 0.3 m of the grenade, the children would have a 50% chance of lethality due to the primary injuries which they sustained.

6 Distance Bowen et. al. 5. Acknowledgements CWVP predicted from 1968 predicted injury level charge injury level Duarte Goncalves is acknowledged for his 0.5 m Less than 1% Greater than 50% contribution to researching hand grenade incidents chance of lethality chance of lethality that occurred near Mthatha over the last ten years. 1 m Threshold for lung Trace to moderate Professor Manfred Held provided valuable practical damage injury insight into the physics behind explosive event 15 m No lung damage No injury research and the relevance of certain parameters in predicting injuries. The NATO RTO HFM- 148/RTG workgroup provided a forum at which to discuss injury criteria relevant in predicting injuries, Table 2: Descriptions of primary injury levels including overpressure injuries, within protected predicted at various distances from the 106 g vehicles. spherical TNT charge.

References Predictions of injury severities at distances of less than 0.5 m from the grenade are not included in H. Axelsson and J. Yelverton. 1996. Chest wall Table 2 as simulated pressure profiles at 0.1 m and velocity as a predictor of nonauditory blast injury in 0.2 m from the explosive charge have positive- a complex wave environment, The Journal of phase durations of less than 0.4 ms. The validity of Trauma, Vol. 40 (3s), pp. S31-S37. the Bowen criterion for pressure profiles with positive-phase durations less than 0.2 ms (Bowen, C. Bass, K. Rafaels and R. Salzar. 2006. Fletcher and Richmond, 1968) or 0.4 ms for the Pulmonary injury risk assessment for short-duration CWVP criterion (Axelsson and Yelverton, 1996) blasts, Personal Armour Systems Symposium has yet to be determined. Further research is (PASS). required to develop criteria suitable for this loading regime. A. Bouamoul, K. Williams and H. Levesque. 2007. 4. Conclusions and recommendations Experimental and numerical modelling of a mannequin for the assessment of blast rd This study focussed on the explosive charge incapacitation and lethality under blast loading. 23 contained in an M26 hand grenade. However, International Symposium on Ballistics, Tarragona, pressure based injury criteria can be applied to Spain. many different explosive event scenarios. A few of these include: I. Bowen, E. Fletcher and D. Richmond. 1968. Extimate of man’s tolerance to the direct effects of • The development and testing of body blast. Technical progress report no. DASA-2113. armour for humanitarian de-mining Washinton, DC, Defense Atomic Support Agency, purposes; Department of Defense. • Validation testing of armoured vehicles to

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