Tear gas

Tear gas is a chemical substance used to control large crowds. It is formally known as a lachrymatory agent or a lachrymator. This name comes from the word for tears. While many people call it a gas, it is actually made of aerosolized solid or liquid compounds. These tiny particles float in the air like a mist.

This substance is used by military forces and law enforcement. It is designed to cause immediate physical discomfort to force compliance. However, its use is strictly regulated by international law when used in war.

The mechanism of tear gas involves the irritation of mucous membranes. These are the moist linings in the eyes, nose, mouth, and lungs. When these particles touch the body, they stimulate specific nerve endings. Specifically, they act on TRPA1 ion channels found on nociceptors. These are sensory receptors that signal pain to the brain.

The result is intense eye pain, heavy tearing, coughing, and difficulty breathing. In some cases, it can even cause temporary blindness. For CS gas, these symptoms usually appear within 20 to 60 seconds. Most people feel better within 30 minutes of leaving the area.

There are several different types of lachrymatory agents. One common type is CS gas, which is the most widely used today. Another type is CN gas, also known as phenacyl chloride, which has the most recorded toxicity. Other agents include pepper spray, known as OC gas, and PAVA spray, or nonivamide. Older agents include bromoacetone and xylyl bromide. Some people also use the term "mace" to describe these substances. This name comes from an early brand of commercial self-defense spray.

The history of tear gas is closely tied to modern warfare. During World War I, it was the most common type of chemical weapon. In August 1914, the French used ethyl bromoacetate in combat. Later that year, Germans used a lung irritant called Nerst Ni-Shrapnel against British and Indian troops. In January 1915, xylyl bromide was used against Russian forces. Because of these dangers, the Geneva Protocol of 1925 was created. This treaty prohibits the use of asphyxiating gases or similar substances in warfare.

While many states signed it, the United States did not ratify the protocol until 1975.

Using tear gas carries significant risks of injury or death. A direct hit from a heavy metal canister can cause skull fractures or even death.

In the 2019–20 Chilean protests, some people suffered permanent loss of vision from canister impacts.

In Portland, Oregon, during 2020, 93.8% of protesters reported physical or psychological health issues after exposure. Furthermore, Venezuelan chemist Mónica Kräuter found that 72% of the tear gas used in Venezuela was expired. She noted that expired gas can break down into dangerous substances like cyanide oxide and phosgenes.

Long-term health effects are also a serious concern. Exposure can lead to respiratory illnesses or permanent eye diseases. These include glaucoma, cataracts, and traumatic optic neuropathy. Skin exposure can cause chemical burns or allergic contact dermatitis. People with asthma are at a much higher risk of needing hospitalization.

Because the particles can stick to surfaces, clothes and shoes must be washed well. If not treated, these particles can remain active for up to a week.

People have developed many ways to defend against these agents. Some use gas masks, respirators, or even swimming goggles.

In Hong Kong, protesters used traffic cones to extinguish canisters.

Others use water or saline to rinse their eyes. Some activists have even used diluted antacids like Maalox to help with skin pain.

These methods show how people adapt to the presence of chemical irritants in public spaces.