Background

In recent years, there has been significant attention to the number of popular protests challenging governments and other powerful actors.1 2 In many cases, police and security forces have responded in ways that fundamentally undermine freedom of peaceful assembly and often lead to escalation through the unnecessary and disproportionate use of force.3–5 Such use of force often involves crowd-control weapons (CCWs) that cause preventable injury, disability and death.

Kinetic impact projectiles (KIPs), commonly called rubber or plastic bullets, are CCWs that are designed to incapacitate individuals by inflicting pain or sublethal injury. Some KIPs target an individual with a single projectile, while others target a group by scattering multiple projectiles.6–8 Manufacturers produce more than 75 different types of bullets and launchers in many countries, including Brazil, China, Israel, South Africa, South Korea and the USA,9 10 and are marketed to military, police and private security forces throughout the world.11 Despite the widespread use of KIPs and the numerous types available, there is limited regulation of the development of these weapons and limited public information provided by manufacturers on their design and guidelines for use.12 13

All projectile weapons function by transferring kinetic energy from a weapon into the body of an individual. Ballistics data indicate that denser objects and faster projectile speeds increase the force of impact.14 KIPs have a wide range of variables that can impact injury patterns and severity, including the material composition, shape, number, muzzle velocity (projectile speed exiting the weapon) and flight path of projectiles, the firing distance and the location of impact on the body.15 It is important to note that many KIPs have muzzle velocities equal to those of live ammunition. Most KIPs are designed with a large surface area to produce a rapid loss of speed during flight and reduce the chance of skin penetration, but this also results in unpredictable flight paths and reduced accuracy.16 Newer weapons include projectiles with a hard outer shell coating, tear gas or pepper spray that explodes on impact, and ‘attenuated energy projectiles’ with hollow tips to limit the risk of ricochet or penetration.17

KIPs can cause blunt and penetrative injuries, ranging from localised contusions to severe organ damage and death.18–20 While there has been much recent media attention globally on the significant dangers of misusing these weapons,21–28 efforts to provide systemic documentation on injuries is limited for a number of reasons. There are limited regulations on the development of weapons, and manufacturers are not required to keep records on injuries from their products in development, field trials or actual use,17 In most countries, there is no legal requirement for law enforcement to collect data on injuries from KIPs.11 Though police may record related deaths, these data are often not publicly available or complete.29 Similarly, military data on both international and domestic use of these weapons is confidential. There is often limited communication between the healthcare providers who treat and manage injuries and police who typically use the weapons.30 While non-governmental organisations and human rights groups may report injuries or deaths in specific incidents, they have not established surveillance mechanisms to systematically collect injury data.11 31 In addition, most of the medical literature on KIPs is sourced in case reports and case series.32 Retrospective cohort studies and prospective studies have been conducted but have been limited to specific locations and time frames and by challenges in developing adequate studies of weapons injuries in potentially volatile and politically difficult conditions.

Given the limited knowledge of the health consequences of KIPs, we undertook a systematic review of the literature to evaluate the morbidity and mortality associated with these weapons. We assessed injury type and severity as well as potential exacerbating and mitigating factors. The present study is part of a larger effort by Physicians for Human Rights and the International Network of Civil Liberties Organizations to research the health effects of weapons commonly used in crowd-control settings and develop recommendations to avoid preventable injury, disability and death.