Chemicals In Defensive Sprays

A number of chemicals, with different functions, are present in defensive chemical sprays. These chemicals can be divided into three categories:  Active Ingredients, Propellants, Carriers.

Active Ingredients are the chemicals that irritate the eyes and respiratory system. There are two basic types of active ingredients: tear gas (CN and CS) and pepper (OC). The active ingredients may be used individually or in combination.

Both CN and CS cause the eyes to burn and tear, and the moist areas of the skin to sting and burn. CS also causes coughing and tightness in the chest.

Contrary to its common name, tear gas is not a gas but a white, crystalline powder, similar in appearance to talcum powder. To get tear gas to its intended target rapidly, it is dispersed as an aerosol cloud of finely divided particles.

CN crystals vaporize more quickly than CS crystals, and therefore are eliminated from skin and clothing sooner than CS, but CS is effective at somewhat lower concentrations than CN.

In the concentration used in defensive sprays, the irritative effects of either CN or CS usually subside in less than 45 minutes after the affected individual is moved to fresh air.

Another active ingredient in defensive sprays is oleoresin capsicum, commonly referred to as OC. OC is a natural, oily, resin-like substance derived from hot peppers, the same peppers used to "heat up" spicy foods. Defensive sprays that contain OC, usually referred to as "pepper sprays," induce an almost immediate burning sensation of the skin and a burning, tearing, and swelling of the eyes. If OC spray is inhaled, the respiratory tract becomes inflamed resulting in a swelling of the mucous membranes lining the breathing passages and temporarily restricting breathing to short, shallow breaths. CN and CS also cause tearing and respiratory discomfort, but they do not have the same inflammatory and swelling effects of OC.

The amount of OC in a pepper spray is usually marketed as a percentage, by weight, of the other ingredients in the spray. However, this percentage cannot always be used to compare the "hotness" of different pepper sprays. Here’s why: The component of oleoresin capsicum that gives it its hotness is the chemical capsaicin. Therefore, the hotness of OC is directly related to the amount of capsaicin in it, which varies significantly from manufacturer to manufacturer. The amount of capsaicin in OC is rated in Scoville Heat Units (SHUs), and can range from a few thousand to several million SHUs. An OC having a SHU rating of 500,000 yields a 10% spray rated at one-tenth the hotness of the original OC, or 50,000 SHUs. But a different OC with a rating of 2,000,000 SHUs yields a 10% spray containing 200,000 SHUs, which is four times as hot as the first spray, even though both can be marketed as 10% pepper sprays.

To compare the hotness of two different pepper sprays, contrast the total number of Scoville Heat Units (SHUs) or the dry weight of capsaicin in the sprays, not the percentage of the OC in the sprays.

In the concentration used in defensive sprays, the irritative effects of OC usually subside in less than 45 minutes after the affected individual is moved to fresh air.

Propellants are the chemicals that create the pressure that allows a tear gas and/or pepper solution to be sprayed from a canister.

Propellants are compressed gases, such as carbon dioxide or nitrogen or liquids that evaporate easily, such as propane of DymelÒ 134 A.

Some propellants are flammable, and care should be taken to avoid spraying these propellants near sparks or open flames.

Propellants may be affected by temperature. Most aerosol canisters can burst if exposed to prolonged 120° F heat, a temperature that can be reached in the interior of an unventilated vehicle parked in the direct sunlight on a hot day. Prolonged exposure to temperatures below 32° F may reduce pressure, resulting in slower discharge.

Carriers are the liquid chemicals used to dissolve tear gas crystals and to dilute OC solutions. Carriers consist of a single chemical or a mixture of chemicals and are usually organic solvents, such as alcohol, acetone, methylene chloride, trichloroethane, or propylene glycol. Water is sometimes added to these solvents to reduce their flammability but tear gas crystals and OC solutions are not easily soluble in water. Therefore, the amount of water added must be carefully measured to ensure that the active ingredients are adequately solubilized.

Home Page