The Chemistry of War: Non Lethal Weapons Tear Gas

an entry by Mika Thomas, Helen Sakharova, Ko Cheng Chan

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Figure 1: A Us soldier wearing a gas mask while traveling through a field filled with tear gas during a training drill

The human body is wonderfully capable of quickly responding to its environment.  Different substances trigger different reaction in the human body.  Tear gas, or a lachrymator, is a substance that interacts violently with the mucosal membranes such as the eyes, mouth, nose and lungs.  Tear gas is actually not a gas, but a colloid, more specifically, an aerosol.  The chemical structure of tear gas is what causes it to affect us differently than other substances.

    Pepper spray also applies to the definition of a tear gas however, unlike CN gas, it is considered an inflammatory agent.  Pepper spray causes painful swelling of capillaries in the eyes and caused temporary blindness.   Pepper spray is relatively simple compared to CN and CS gases.  As the name would suggest, it is derived from peppers.  Peppers contain a group of chemicals called capsaicin.  Pepper spray is also referred to as OC spray, Oleoresin Capsicum spray.  A capsaicin is a colorless irritating phenolic amide C18H27NO3  and is responsible for giving peppers their pungent spicy flavor.  Capsaicins’ molecular structure enable them to bind directly with proteins found in the membranes of pain sensing neurons.   This causes a victim to feel an intense burning sensation, excess salivation, excess mucous production, and even vomiting.  Therefore, pepper spray should be used wisely.   The difference between sweet peppers and the infamously painful ghost pepper is the concentration of capsaicin that they both contain.

This concept of concentration also plays strongly into the potency of pepper sprays and tear gases.  Different states have different laws on the limit of capsaicin that can be used for personal protection.  Even so, for almost all pepper sprays, a 1 second blast can render a person incapacitated for fifteen minutes to an hour. Different brands of pepper spray contain different amounts of solvents such as alcohols, and water.   The more dilute the concentration of capsaicin, the less potent the spray will be.  Like other forms of tear gas, pepper spray is canned under extremely high pressures and this results in an average can of pepper spray having a shooting range of about 10 feet.  More application differences between CN gas and pepper spray can be read about here.chem chem.png

Figure 2 : an image of a molecule of capsaicin.  The black balls represent carbon atoms, the white balls represent hydrogen atoms, the blue ball represents an atom of nitrogen and the red balls represent oxygen atoms.

    Tear gas is qualified as a nonlethal weapon, but there are serious risks involved.  Tear gases qualify as a type of chemical warfare and are prohibited in war by many international warfare treaties.  However, tear gases are allowed to be used by branches of the military for training.  Tear gases are use used normally for domestic riot control or personal protection.    CN (chloroacetophenone) gas, CS (chlorobenzylidenemalononitrile)) gas and bromoacetone are the types of tear gases used by law enforcement.  A familiar form of CN gas is Mace, a popular trademark brand of CN gas sold for personal protection.

    CS gas is normally composed of a white powder mixed in a dispersal agent like methylene chloride. At standard temperature and pressure, CS forms a white crystal with a low vapour pressure and poor solubility.  CS crystals are converted into microparticulate clouds by pyrotechnic devices.  CS gas may seem to be a continuous solution or a gas, but it is also a colloid.

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Figure 3: An image of a Us soldier wearing a gas mask to avoid the painful, yet temporary effects of CS gas. CS gas appears to be a white gas, but it is composed of small particles of white solid.

    As a result, CS gas is usually stored in cans at high pressures. A can of CS contains a gas and skin irritating solvents. When this can is used, highly pressurized gas escapes a can and the gas carries ultra-fine particles of CS.  The powdered CS becomes attached to the mucous membranes of organisms. The physical effects of CS gas is felt almost immediately.  A person’s breathing rate slows and excessive use of CS gas can lead to death. The poor solubility of CS makes it that it can exist on a mucous membrane for a long period of time if not physically removed.  Luckily, wind and fresh air can removed CS particles from the skin.  Gas masks work by protecting ones mucous membranes.

    Because it has been dubbed a nonlethal weapon there is fear that authoritative forces use it too liberally.    Tear gas is technically a “less-than-lethal” weapon because it can, in some cases, lead to death.  There is controversy over allowing authoritative forces to use tear gas.  Often, law enforcers must be exposed to tear gas themselves before they gain the right to use it.  While the memory f the pain of peppery spray might stop a young officer from using it too much, an older officer might not remember the pain and use it too often.  CN gas is excruciatingly painful and is often used on protesters as shown below.  The use of tear gas has raised social controversy that has even inspired for scientific research to be conducted on tear gases.  chem riot.jpg

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