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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Conclusion: Tear Gas, Pepper Spray, and Chemical Weapons (Oh My!) 

According to reputable official the Honorable Mr. Andrew C. Weber, the Assistant Secretary of Nuclear, Chemical, and Biological Defense programs, “the Office of the Assistant Secretary of Defense for Nuclear, Chemical and Biological Defense Programs has a wide range of duties related to countering Weapons of Mass Destruction (WMD) threats.  Their team of top scientists helps us understand these threats and engage in activities and programs to counter them.  Their duties include overseeing Department of Defense science and technology investments in countermeasures that will enable the United States forces to prevent, protect against, and respond to WMD threats”. However there is still one chemical weapon that is marketed to the masses today and even used against protests: tear Gas.

 

Tear gas was first introduced World War I by the French. It was not very concentrated, and the Germans hardly noticed it was being used. In August 1914, the French fired 26 mm grenades containing ethyl bromoacetate, but the low concentration, only approximately 19cm³ per grenade, was not enough to bother the Germans. Afterwards, due to shortages of bromine, the primary chemical was switched to chloroacetone. The Germans then retaliated with a tear gas of their own making, using it for the first time in October of 1914 on the British. Again, the weapon was so dilute that the enemy combatants did not even notice.

Peaceful protesters in Tahrir Square attempt to flee from the noxious tear gas

 Since its debut in the Great War, tear gas, and its famous derivative pepper spray, has transformed from an ineffective weapon of war to a highly efficient tool for dispersing protesters. It has become a lynchpin in the arsenal of modern authoritarian regimes and has seen widespread use in recent years, with the Arab Spring and the Turkish protests being the more high-profile international cases. In an especially ironic incident, tear gas manufactured in the US, the great champion of democracy, was used on protesters in Tahrir Square attempting to enact some democratic reform. In Turkey, when Prime Minister Erdogan tried to seize historic sites and develop them for his cronies, protesters invaded Taksim Square; they were tear gassed. Luckily for them, the tear gas brought international attention to their plight, but that cannot be said of all tear gas victims.

A doctored photograph which emphasizes the inhumane actions of Lt. Pike, who had pepper sprayed a peaceful protestor.

 

Another event exemplifying the political, rather than physical, power tear gas can have was the UC Davis Occupy protest that involved Lt. Pike, a police officer who had pepper sprayed a peaceful protester for no apparent reason. The ensuing media firestorm brought new attention to the waning Occupy Movement, showing that chemical weapons aren’t always so bad. Also, the image of the cop pepper spraying the protesters birthed many amusing pictures, another positive effect of chemical weapons.

3-D Model of 2-Chlorobenzalmalononitrile (CS)

Although tear gas has numerous different forms, 2-Chlorobenzalmalononitrile (also known as CS) is the most common. CS has a chemical formula of C10H5ClN2, composed of several cyanide functional groups, Due to the hydroscopic nature of aerogels, a type of colloid, when silica aerogel is combined with CS, the fluidity, water resistance, chance of exposure and intensity of the symptoms increase.  CS gas is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile through Knoevenagel condensation. This reaction is composed of two steps: first, the nucleophilic addition of an active hydrogen compound to a carbonyl group and second, a dehydration reaction in which a molecule of water is removed. of the symptoms increase

CS-chemical-synthesis.png

ClC6H4CHO + H2C(CN)2 → ClC6H4CHC(CN)2 + H2O

There are a couple major components in tear gas. Charcoal is used as an ignitor when combined with potassium nitrate allowing the can to combust. This is because potassium nitrate gives off great quantities of oxygen when it burns, feeding the fire, while charcoal will begin to smolder when the pin is pulled. Silicon is also added so that when the exothermic reaction of potassium nitrate occurs causing super hot glass droplet to forms, igniting the other compounds. The sucrose in the can acts as a fuel source for the fire at a relatively low temperature, vaporizing the O-Chlorobenzalmalononitrile, a lachrymator, irritating the eyes or the nose. Potassium chlorate is an oxidizer creating some of the smoke, while magnesium carbonate is used to to keep the solution slightly neutral. This is all dispersed in nitrocellulose, a sticky binding, to create a homogenous mixture.

Although technically banned under the UN Convention on Chemical weapons, tear gas is not nearly as lethal as other compounds such as Ricin or Sarin gas. In fact it has to be 25 grams per cubic meter for it be lethal when only concentrations 4 grams per cubic meter are used to disperse crowds. However it is still worrying to note that chemical weapons are not just abstract concepts, created in sinister labs in shady countries, but actually used today, even here in the US.

Conclusion: Tear Gas, Pepper Spray, and Chemical Weapons

 

According to reputable official the Honorable Mr. Andrew C. Weber, the Assistant Secretary of Nuclear, Chemical, and Biological Defense programs, “the Office of the Assistant Secretary of Defense for Nuclear, Chemical and Biological Defense Programs has a wide range of duties related to countering Weapons of Mass Destruction (WMD) threats.  Their team of top scientists helps us understand these threats and engage in activities and programs to counter them.  Their duties include overseeing Department of Defense science and technology investments in countermeasures that will enable the United States forces to prevent, protect against, and respond to WMD threats”. However there is still one chemical weapon that is marketed to the masses today and even used against protests: tear Gas.

Tear gas in use

Tear gas was first introduced World War I by the French. It was not very concentrated, and the Germans hardly noticed it was being used. In August 1914, the French fired 26 mm grenades containing ethyl bromoacetate, but the low concentration, only approximately 19cm³ per grenade, was not enough to bother the Germans. Afterwards, due to shortages of bromine, the primary chemical was switched to chloroacetone. The Germans then retaliated with a tear gas of their own making, using it for the first time in October of 1914 on the British. Again, the weapon was so dilute that the enemy combatants did not even notice.

Peaceful protesters in Tahrir Square attempt to flee from the noxious tear gas

Since its debut in the Great War, tear gas, and its famous derivative pepper spray, has transformed from an ineffective weapon of war to a highly efficient tool for dispersing protesters. It has become a lynchpin in the arsenal of modern authoritarian regimes and has seen widespread use in recent years, with the Arab Spring and the Turkish protests being the more high-profile international cases. In an especially ironic incident, tear gas manufactured in the US, the great champion of democracy, was used on protesters in Tahrir Square attempting to enact some democratic reform. In Turkey, when Prime Minister Erdogan tried to seize historic sites and develop them for his cronies, protesters invaded Taksim Square; they were tear gassed. Luckily for them, the tear gas brought international attention to their plight, but that cannot be said of all tear gas victims.

A doctored photograph which emphasizes the inhumane actions of Lt. Pike, who had pepper sprayed a peaceful protester.

Another event exemplifying the political, rather than physical, power tear gas can have was the UC Davis Occupy protest that involved Lt. Pike, a police officer who had pepper sprayed a peaceful protester for no apparent reason. The ensuing media firestorm brought new attention to the waning Occupy Movement, showing that chemical weapons aren’t always so bad. Also, the image of the cop pepper spraying the protesters birthed many amusing pictures, another positive effect of chemical weapons.

3-D Model of 2-Chlorobenzalmalononitrile (CS)

Although tear gas has numerous different forms, 2-Chlorobenzalmalononitrile (also known as CS) is the most common. CS has a chemical formula of C10H5ClN2, composed of several cyanide functional groups, Due to the hydroscopic nature of aerogels, a type of colloid, when silica aerogel is combined with CS, the fluidity, water resistance, chance of exposure and intensity of the symptoms increase.  CS gas is synthesized by the reaction of 2-chlorobenzaldehyde and malononitrile through Knoevenagel condensation. This reaction is composed of two steps: first, the nucleophilic addition of an active hydrogen compound to a carbonyl group and second, a dehydration reaction in which a molecule of water is removed. of the symptoms increase

CS-chemical-synthesis.png

ClC6H4CHO + H2C(CN)2 → ClC6H4CHC(CN)2 + H2O

There are a couple major components in tear gas. Charcoal is used as an ignitor when combined with potassium nitrate allowing the can to combust. This is because potassium nitrate gives off great quantities of oxygen when it burns, feeding the fire, while charcoal will begin to smolder when the pin is pulled. Silicon is also added so that when the exothermic reaction of potassium nitrate occurs causing super hot glass droplet to forms, igniting the other compounds. The sucrose in the can acts as a fuel source for the fire at a relatively low temperature, vaporizing the O-Chlorobenzalmalononitrile, a lachrymator, irritating the eyes or the nose. Potassium chlorate is an oxidizer creating some of the smoke, while magnesium carbonate is used to to keep the solution slightly neutral. This is all dispersed in nitrocellulose, a sticky binding, to create a homogenous mixture.

Although technically banned under the UN Convention on Chemical weapons, tear gas is not nearly as lethal as other compounds such as Ricin or Sarin gas. In fact it has to be 25 grams per cubic meter for it be lethal when only concentrations 4 grams per cubic meter are used to disperse crowds. However it is still worrying to note that chemical weapons are not just abstract concepts, created in sinister labs in shady countries, but actually used today, even here in the US.