The scenes of violent confrontation in Ferguson, Missouri, over three straight nights show angry African-American residents protesting in response to a police shooting currently under investigation. To counter the crowds, local police have attempted to use the same techniques that security forces use around the world, including tear gas, bean bag rounds and wooden bullets. Riot control police – wearing helmets, visors, body armor and gas masks – are called in for disturbances ranging from rowdy soccer matches and merchandise looting to anti-war protests. Civil disorder, whatever the source, can be quelled with a variety of methods, increasingly taken from the military arsenal:

Tear gas

Deployed at demonstrations from Tahrir Square to Port-au-Prince to prevent looting, disperse crowds and promote security, one of the most commonly used riot control agents around the world is tear gas. Known as a “lachrymatory” substance for the irritation that generates teary eyes and difficulty breathing, the chemical is usually discharged from a canister that is fired from a grenade launcher towards a crowd. CS and CN are most frequently used gases. Dispenser methods include backpacks and even drone attachments for larger aerial volumes. Pepper spray is another lachrymatory agent, whose effects can last up to two hours, considerably longer than normal tear gas. The active ingredient, capsaicin, is sprayed directly onto people – as at a 2011 tuition-hike protest at the University of California, Davis. In Ferguson, MO, police have attempted to disperse protesters using smoke bombs – fireworks that generate smoke after ignition. A similar projectile can be used by police to break up crowds: stun grenades. Also known as flashbang, these non-lethal explosive devices create a blinding light and loud noise to disorient people.

Baton rounds

This category includes four separate but related types of crowd control: rubber bullets, plastic bullets, wooden bullets and bean-bag rounds. Rubber bullets, which are sometimes just rubber-coated steel bullets, can be fired from normal firearms or dedicated riot-control weapons. They are used as a non-lethal alternative to standard metal bullets but often cause significant pain and result in hematomas and contusions. As with similar weapons, they are more dangerous when fired from close range. When aimed at people’s heads, they can cause fatal damage. Plastic bullets were developed by British forces to use in Northern Ireland to be more safe than rubber bullets, and carried less risk of ricocheting uncontrollably. Used to quell the recent Missouri violence, wooden pellets also cause bruises and welts. Shot from a distance, the ammunition is intended to administer “pain compliance.” Police in Oakland agreed in 2004 to stop using this technique after a lawsuit. Bean bag rounds, also referred to as "flexible baton rounds," are fired as shells from a regular 12-gauge shotgun – often with a bright colored tag to differentiate the weapon. The lead shot disperses in the air within a small fabric sack, spreading impact over one square-inch on the target. The blow often causes a muscle spasm, temporarily disabling the subject. This method has on average caused one death per year in the U.S. So as not to cause internal bleeding or disrupted heartbeat, officers are instructed to aim at extremities. During Occupy protests in Oakland, veteran activist Scott Olsen’s skull was fractured by a bean bag round.

Liquid fire

When standard police vehicles are not sufficient for forcefully deploying riot officers, a department often sends horse-mounted units, busloads of additional policemen and armored vehicles, such as Mine-Resistant Ambush Protected (MRAP) jeeps. Water cannons can spray a high-velocity stream and were first used on fireboats, before being truck-mounted in the 1930s. They were widely used during the Civil Rights Movement. While advocacy groups and vendors disagree on what form of riot control is most safe or effective, water cannons are not widely used in the U.S. today. However, they are used in police crackdowns in other countries, from student marches in Chile to demonstrations against gang rape in India. Stink bombs or liquids causing a foul odor are sometimes used, and testing has been done on sticky foam that can immobilize rioters. Moreover, Israeli soldiers in the West Bank often use “skunk water” to disperse protesters.

Physical barriers

Known as kettling or corralling, police use “containment” tactics to cordon off a crowd and either direct people towards one exit or prevent them from leaving the area entirely. The method is seen as controversial because it often traps bystanders in the same location and has been criticized as a violation of civil liberties. Trapping protesters in a confined space stops other individuals from joining and can divide a long march up into several enclosed sections to minimize mobility for the crowd. Sealing access roads and exits often tires out protesters, and gives police an opportunity to videotape or photograph people who might later be arrested. To disperse a crowd, security forces can move quickly in a coordinated line towards the gathering. “Baton charges” are generally only used as a last resort. Clubs and riot shields raised can inflict pain, forcing people away from the scene due to the actual impact or just the fear of being struck. To prevent confrontations beforehand, long metal “bike racks” are used at public events in controlling the movement of large numbers of people attending parades, rallies and festivals. Organizers of such events deploy these objects at the venue to manage crowds. At mass gatherings, these provide a psychological and tangible way of pushing individuals away from accessing certain zones. Temporary fencing can enhance public safety or provide theft deterrence. Composed of steel or lighter-weight plastic, such barriers are often joined to prevent them from being knocked down, and the standard height is 43 inches. Wooden sawhorses with the writing “Police Line – Do Not Cross” were formerly used for the same purpose.

Wave weapons