Written by Kevin Cresswell
Obscurants are anthropogenic or naturally occurring particles suspended in air that block or weaken the transmission of particular parts of the electromagnetic spectrum, such as visible and infrared radiation or microwaves. Smokes are produced by burning or vaporizing some product.
Since World War II, Hexachloroethane (HC) screening smoke grenades have been in use. Smoke grenades have multiple roles on the battlefield, from providing soldiers with cover while in combat and signaling landing zones, to identifying friendly troops and isolating the location of enemy targets. They are also used by law enforcement, and industry for testing seals for example.
Military application of phosphorus smokes for screening during a military operation can make use of either white phosphorus (WP) or red phosphorus (RP). WP is the most effective smoke agent to defeat thermal imagery systems.
Grenades generally produce smoke by igniting a chemical reaction inside of a canister and releasing the resulting smoke through holes in the top and bottom of the canister. The ignition that sets off this process makes smoke grenades a potential fire hazard, or in worse case scenario an explosive hazard in the right environment.
The Grenades in use with the U.S Military are the M18 grenade, the M713, M715, or M716 40-millimeter (mm) cartridge, for signaling and marking and, in some cases, for training to simulate exposure to chemical-warfare agents. Developed in 1942, the M18, was designed to replace the M16 smoke grenade, which did not burn as long or as vividly. It was designated standard issue in the fall of 1943. Both were produced at the same time as the M16 production lines were already setup when the M18 was adopted. The M16 was available in red, orange, yellow, green, blue, violet, and black. The M18 initially were going to be produced in the same colors, including white, but it was decided to limit it to four colors (red, yellow, green and violet) for simplicity. The M16 was declared limited standard in 1944 but was still available when it was declared obsolete in the early 1990s.
Smoke was used during the Vietnam war. When a ground element popped smoke to identify its location to aircraft, the aircraft was not told the color, but told to identify the color they saw. This prevented the VC/NVA if monitoring the frequency from popping smoke of the same color to confuse the aircraft. For additional security the colors were sometimes identified as cherry (red), lime (green), lemon or banana (yellow), or grape (violet). The violet-colored smoke grenade of World War II, was used in-theater because of its vivid color; previously it was only used in the United States for training. Its smoke was more toxic than the other color mixtures and was removed from the inventory after the end of the Cold War in the 1990s.
The green-colored smoke grenade was still used in Southeast Asia because the jungle undergrowth was a different color and would still contrast with it. It was discovered that the green smoke drove away swarming bees.
While highly effective for the reasons stated above, research has been underway for many years to produce compositions from which to form obscurants that balance the performance, manufacturing cost, environmental impact, the availability of materials, and importantly, toxicity.
Army researchers have identified lithium perchlorate (LiClO4) and boron as fundamental chemicals in a new smoke grenade. This composition has reduced toxicity that is produced without the use of organic liquids which add to air pollution. The composition produces boron oxide (B2O3) and lithium chloride (LiCl). A virtually undetectable amount of boron trichloride (BCl3) and chlorine gas may be by-products of the composition. The grenades may be used by the military in battlefield situations or for training, and by the civilian sector for firefighter training and crowd dispersal situations.
HC toxicity is a result of the production of zinc chloride which is corrosive and astringent, and known to cause burning in the respiratory and gastrointestinal tract. Zinc chloride smoke bomb exposure is frequently seen in military drills, combat exercises, metal industry works, and disaster simulations. Smoke exposure presents a variety of pulmonary damage based on the intensity of the exposure. It can damage nerve endings in the nasal passages and cause eye burns. Smoke induced severe acute respiratory distress syndrome (ARDS) is often fatal and there are no standard treatment guidelines. The first case of zinc chloride smoke bomb inhalation injury was reported in 1945.
The addition of tiny particles vaporized or combusted with a specific pigment or dye in the aerosol influences the color of the smoke. This mixture generally consists of a cool-burning formulation with lactose, potassium chlorate oxidizer, or dextrin as the fuel. Single or multiple dyes are then added to an amount equal of about half of the mixture, and a small amount of sodium bicarbonate is used as a coolant.
The demand for smoke grenades grew after the early years of the Iraq War, when there was more fighting in urban areas (FIBUA), and troops needed cover when moving from building to building. At the time troops preferred using colored smoke instead of white because the chemical in the white smoke “hurt their eyes.”
The military rapidly depleted its large stockpile, and the U.S. government turned to Nation Ford Chemical’s (NFC), expertise, in business since 1994. The company, from S.C., produces specialty organic chemicals and has been the only domestic supplier of four color dyes – yellow, green, red and violet – used in smoke grenades for the U.S. Army. T
There really is no specific meaning for any color, every color of smoke grenade has the potential to mean anything. Potential uses include marking the location of wounded soldiers, providing a target for an air strike and marking the location of friendly troops in need of extraction, etc. Different colors used as visual signals are often so that the ground/ground and ground/air forces could coordinate and know which smoke was friendly. The in Vietnam the VC were using smoke to get helicopters to land in the wrong place and then get ambushed, so different colors allowed the pilots to know where the friendly’s were, eg; “LZ 1 is Blue.”
The advent of paint balling and online gaming has presumed that the following colors are generally accepted in military circles; White = Used for concealment (No marking use), Green = Friendly Forces, Blue = Friendly Forces and/or LZ, Purple = LZ/Medevac LZ and Red = Hostile Target.
NFC already made the yellow dye required for the smoke grenades, but their product was destined for the plastic market and didn’t meet military specifications. To meet the stringent density and particle size requirements, they invented new manufacturing techniques. Since they made these four dyes, the DoD has looked at new dyes that are better for the environment and the troops and Nation Ford has continued to help to develop new, more sustainable dyes.
The different colors are produced by using the following composites:
- Violet: Solvent Violet 13 (C21H15NO3)
- Green: Quinizarine Green SS (C28H22N2O2)
- Orange: Sudan I (C16H12N2O)
- Blue: Victoria Blue BO (C33H41N3O – hydroxide)
- Yellow: Aniline Yellow (C6H5N=NC6H4NH2)
- Red: Sudan IV (C24H20N4O).
The world’s Air Force Aerobatic Teams regularly use a specifically formulated liquid dye and an oil, which does not contain any chlorinated solvents. If the smoke was generated through combustion, it would be hazardous for use in aircraft due to the risk of explosion. Therefore, testing the oils and dyes before the performance is required to eliminate any risk posed for the pilot, due to contamination of the oil or dye by highly combustible elements. The safety of the spectators watching at 1500 ft or below can be secured, by making sure that the amount of harmful solvents in the mixture is not high. The environmental impact of these oils and dyes should be taken into account as a key quality control aspect.
In the presence of dangerous chemicals during drug raids, or when a warfighter is attempting to signal an incoming aircraft, removing the ignition from a smoke grenade would mean safety for the user as well as any innocent bystanders and their property. since smokeless powder replaced black powder as the standard propellant for guns and firearms, the armed forces have sought methods to blanket battlefields by creating a haze similar to that created by black powder.
In order to reduce the likelihood that exposure to smokes and obscurants during combat training would have adverse health effects on military personnel and the general public residing or working near military-training facilities, the Office of the Army Surgeon General requested the National Research Council (NRC) review the data on the toxicity of military smokes and obscurants and recommend exposure guidance levels for military personnel during combat training and for the general public residing or working near military-training facilities.
The NRC assigned this project to the Committee on Toxicology (COT), which convened the Subcommittee on Military Smokes and Obscurants. Volume 3, reviews data for the seven colored smokes used by the Army for signaling purposes. In Volume 1 of this series, the subcommittee evaluated four obscuring smokes: fog oil, diesel fuel, red phosphorus, and hexachloroethane.
Current Army policy regarding colored smokes states that during training, troops must avoid entering the smoke cloud. If troops are required to enter the smoke plume, they must wear a chemical protective mask, long-sleeve shirts, head coverings, pants that cover the entire leg, and boots.
In addition, Army policy requires that personnel involved with production of the M18 colored-smoke grenades and exposed to the pure dyes or smoke formulations wear protective equipment, including coveralls, butyl rubber gloves, head coverings, and respiratory protection. Symptoms follow a biphasic course mainly characterized by dyspnoea, coughing and lacrimation, related to irritation of the airways in the first six hours, followed by reappearance of early signs complemented with inflammation related signs and tachycardia from 24 h onwards. Acute respiratory stress syndrome developed in severely affected individuals. Chest radiographs do not always correspond with clinical symptoms. Common therapy comprises corticosteroids, antibiotics and supplemental oxygen or positive pressure ventilation in 64% of the cases.
The mixture in the smoke grenades used in a paintball match is called cool or cold burning. In this case, no external flame is generated, and the cartridge temperature is lower when compared to military smokes that burn at elevated temperatures. As the smoke grenade mixture is burnt without atmospheric oxygen, it can even burn underwater. Polaris’ CoolSmoke® produces large smoke clouds with a non-incendiary reaction. The fuse for CoolSmoke is non-pyrotechnic and does not produce any sparks. The ignition time, discharge time, and smoke output compares favorably to current industry leaders. The CoolSmoke grenade can be dropped in water, thrown, or launched and has practical applications in law enforcement, military, entertainment/gaming, and as an insecticide.
These capabilities add safety without detracting from the quality of the product, and it can cost as little as half the current price for a smoke grenade produced by current industry leaders.