Police forces that use tear gas wear gas masks to avoid harming themselves, but there are also some low-tech forms of protection. Wearing swimming goggles can protect the eyes, and a damp cloth soaked in a compound like urea can protect the lungs, de Bretton-Gordon said.
Rubber bullets are usually made with a heavy type of plastic or rubber, and are about half an inch to 1 inch (1.3 centimeters to 2.5 centimeters) thick, and about 2 inches (5 cm) long, with a blunt end, de Bretton-Gordon said. The bullets are often used for animal control, but police also occasionally use them to manage protests.
Rubber bullets can cause a lot of pain and can sometimes penetrate the skin, but serious injury is more common when the bullets are fired from a range closer than 65 feet (20 meters), according to a report by Dr. Timothy Hardcastle, deputy director of trauma service at Inkosi Albert Luthuli Central Hospital in South Africa.
Normally, police forces aim low when firing rubber bullets at a crowd, to knock people over rather than cause serious harm. The bullets are also fired at a lower speed than regular ammunition. However, a stray bullet that hits someone in the head or face can be fatal in some extreme cases, de Bretton-Gordon said.
A study published in 2013 in the Journal of Emergencies, Trauma and Shock examined 64 patients who were hospitalized after being hit with rubber bullets during protests in Kashmir from 2008 to 2010. The bullets caused only blunt injuries in 46 patients, but penetrated the skin in 18 patients, killing one when the bullet hit a major artery. The researchers note that younger people and women are more likely to suffer severe injuries, because of their smaller builds.
Police may also use sound cannons to blast the ears of protestors and discourage them from congregating in one place. Several kinds of sound cannons exist, but the ones police forces are using in Ferguson are called Long Range Acoustic Device (LRAD) instruments. LRAD Corporation initially designed the instruments for the U.S. Navy, as part of its Shipboard Protection System used to deter pirates and to hail other ships.
The sound systems are now used by police to communicate with large crowds and send out powerful warning blasts for crowd control. The blasts can reach beyond 6,560 feet (2,000 m), according to LRAD Corporation's website.
Typical human conversations happen at about 60 decibels (dB). A blast of 120 dB or more can lead to hearing loss, according to the Centers for Disease Control. The LRAD model that police appear to be using in Ferguson can reach up to 149 dB, Slate.com reported.
The maximum decibel level for each model is measured from a distance of 3 feet (1 m), E. Brian Harvey, director of investor relations and capital markets for LRAD Corporation, told Live Science in an email. Every time the distance from the instrument doubles, the sound intensity decreases by 6 dB. Covering one's ears reduces the sound intensity by about 25 dB, according to Harvey.
The protests in Ferguson have launched widespread debate on police reform and the need for demilitarization of police forces in the United States.
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