Evaluation of Skin Penetration from Less Lethal Impact Munitions and
Their Associated Risk Predictors
Authors: Foley Sierra , Sherman Donald , Davis Andrew , MacDonald Robert , Bir Cynthia 
Published: September 2023

<div><b>Introduction:</b> The use of less lethal impact munitions (LLIMs) by law
enforcement has increased in frequency, especially following nationwide protests
regarding police brutality and racial injustice in the summer of 2020. There are
several reports of the projectiles causing severe injuries when they penetrate
the skin including pulmonary contusions, bone fractures, liver lacerations, and,
in some cases, death. The penetration threshold of skin in different body
regions is due to differences in the underlying structure (varying degree of
muscle, adipose tissue, and presence or absence of bone).</div>

<div><b>Objective:</b> The objective of this study was to further investigate
what factors affected the likelihood of skin penetration in various body regions
and to develop corresponding penetration risk curves.</div>

<div><b>Methods:</b> A total of eight, fresh/never frozen, unembalmed,
postmortem human specimens (PMHS) were impacted by two projectile sizes: a 1″
and 5/8″ neoprene rubber ball in various body regions. Impacted body regions
included the thigh, abdomen, anterior torso between ribs, anterior torso on a
rib, sternum, scapula, posterior torso on a rib, and lower back for a total of a
minimum of 24 shots per PMHS. To achieve both a penetrating and non-penetrating
shot for each set of impacts, the impact location was assessed post impact to
determine if penetration occurred, and the velocity of the next shot was
adjusted to target the alternate outcome on the contralateral side within the
same body region. Post-test, each PMHS underwent X-rays to determine if any
other additional injuries occurred.</div>

<div><b>Results:</b> A binary logistic regression analysis was performed to
determine which factors (e.g., velocity and energy density) were statistically
significant at predicting the risk of penetration. Energy density was utilized
as the primary predictor to evaluate the two projectiles’ data together and
additional parameters (e.g., skin thickness and BMI) were also tested as
co-factors. Statistical significance was obtained with energy density alone for
the thigh (<i>p</i> = 0.004), anterior torso between ribs
(<i>p</i> = 0.043), lower back (<i>p</i> = 0.04),
scapula (<i>p</i> = 0.03), and posterior torso on a rib
(<i>p</i> = 0.005). The abdomen region was not significant with
energy density alone (<i>p</i> = 0.085) but when BMI was added as a
co-factor significance was found to be (<i>p</i> = 0.021). The sternum
and anterior torso on a rib were not found to have statistical significance with
any of the predictors analyzed. The 50% risk of penetration was found for each
region that had statistical significance. The thigh had a 50% risk at 12.62
J/cm<sup>2</sup>, 22.3 J/cm<sup>2</sup> for the anterior torso between ribs,
28.6 J/cm<sup>2</sup> for the lower back, 33.3 J/cm<sup>2</sup> for the scapula,
and 34.3 J/cm<sup>2</sup> for the posterior torso on ribs.</div>

<div><b>Conclusion:</b> The results support that energy density is a good
predictor for estimating the likelihood of the skin to penetrate and that the
risk of penetration varies by body region.</div>