How Things Work: Tear gas

David Huang Apr 6, 2009

College activists, street protesters, radical civilians, and perhaps perverted stalkers are all familiar with what tear gas is and what it does.
Nowadays, tear gas is usually used by both police for crowd control and by individuals for personal protection. What exactly is tear gas? Moreover, how do you fabricate tear gas yourself at home?

“Tear gas” is a term commonly used to refer to a group of chemicals known as lachrymators, or riot control agents.
Lachrymators stimulate the corneal nerves in the eyes to cause symptoms of tearing, pain, hard breathing, and even temporary blindness.
They attack the sulphur containing compounds in enzymes and irritate the mucous membranes in the eyes, nose, mouth, and lungs.
Some common lachrymatory agents are 2-chlorobenzalmalononitrile (CS gas), phenacyl chloride (CN gas), and oleoresin capsicum (OC spray).
CN gas has been used for personal protection and defense since the 1920s. Phenacyl chloride is usually synthesized by the Friedel-Crafts acylation of benzene using chloroacetyl chloride, along with an aluminum chloride catalyst.

Some of the first such products were tear gas pens and pistols . These gas pens and pistols were able to aim the CN particles at an individual and cause some serious damage. The use of such devices usually results in both mechanical and chemical injuries to the eye.

In 1965, CN was sold by General Ordinance and Equipment Company as a personal protection spray device. It was widely marketed under the brand name Mace. This product gained extreme popularity in the 1960s, and the term Mace is still incorrectly used as a generic term for all aerosol defense spray.
Unfortunately, according to Howard Hu’s article “Tear Gas — Harrassing Agent or Toxic Chemical Weapon?” since the advent of the product, there have been reports indicating the product to have limited effectiveness against some individuals, notably people who are under the influence of drugs and alcohol, or those with certain mental disturbances.

In addition, it can take from several seconds to a few minutes for CN to achieve its full effect, which makes the person using the spray vulnerable to attack during this period of time.

After CN gas, CS gas was first developed by the Chemical Defense Experimental Establishment in Portland, England in the 1950s.
CS gas is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile via the Knoevenagel condensation, in which a hydrogen atom is added to the carbon atom in the compound, and a water molecule is removed.

The reaction is catalyzed by a weak base, such as piperidine or pyridine. The catalyst helps the reaction proceed much faster than it would without the catalyst.
Its useful form is intended to be a smoke or fog of suspended particles. This can form a mist that is very harmful. Since its introduction, CS has predominantly replaced CN as the riot control agent of choice in England and the United States.
It can cause extreme severe skin and mucous membrane irritation even in minute doses. The symptoms caused by CS are also exacerbated in hot or humid weather.

During the Vietnam War, the United States developed the “Mighty Mite,” which is a continuous spray device used in caves and tunnel systems. Although described as a non-lethal weapon, recent studies have shown otherwise.

In his research article “Possible Lethal Effects of CS Tear Gas” Uwe Heinrich stated that under the circumstances in which gas masks are not used and occupants were trapped, “there is a distinct possibility that this kind of CS exposure can significantly contribute to or even cause lethal effects.”
In addition, according to the United States Army Center for Health Promotion and Preventive Medicine, CS gas emits “very toxic fumes” when heated to decomposition, and at specified concentrations, CS gas is an immediate danger to life and health. They also state that individuals exposed to CS gas should seek medical attention immediately.

OC spray, most widely known as pepper spray, is another commonly used tear gas nowadays. It is a much less lethal agent but can be deadly in rare cases.
The active ingredient in pepper spray is capsaicin, which is a chemical derived from the fruit of the plants in the Capsicum genus, including chilis. Pepper spray has effects similar to those of other types of tear gas and can cause a stinging and painful sensation in the eyes. Pepper spray is currently one of the most effective personal protection devices available.
For Carnegie Mellon students who constantly stay in the library until late at night and feel unsafe walking back to their residences, it may be helpful to carry a can of improvised homemade pepper spray that has similar effects.

A step-by-step guide for making tear gas at home:

According to InfoBarrel.com, all you need to make pepper spray are two tablespoons of hot red pepper powder, rubbing alcohol, baby oil, and an empty spray bottle.

1.Put the red pepper powder in a small glass container.

2.Pour rubbing alcohol until it is one centimeter above the pepper powder.

3.Grind the pepper in the alcohol. A spoon or spatula could be used.

4.Continue to grind and stir for at least 10 minutes.

5.Add half a centimeter of baby oil and mix for about two minutes; cover the glass container and shake until well mixed.

6.Try to avoid spilling while shaking the container.

7.To filter the solution, pour it into another container that has a piece of cloth over it.

8.Lastly, put the solution into the spray bottle, clearly labeled to avoid accidents.