Wednesday, July 11, 2012

Through the Smoke: Pyrotechnics and Explosives Branch Creates Safer Grenade for the Warfighter

Edgewood Chemical Biological Center (ECBC) Pyrotechnics and Explosives Branch is making smoke grenades safer for the Warfighter. The branch is working to slow the burn rate and increase the yield factor of grenade smoke by revamping the screening smoke composition for the AN-M8 HC Screening Smoke Grenade. The new screening smoke composition, labeled HX Smoke Composition, will be used as a direct replacement fill for the AN-M8 HC Screening Smoke Grenade, which has been placed into restricted use due to environmental and toxicology issues.

“HX Smoke is one of the most effective smoke screening types we have seen to date because it has the highest extinction coefficient of any of the new smoke candidate compositions,” said Joe Domanico, Chief of the Pyrotechnics and Explosives Branch. “We wanted to be able to use this kind of smoke because it is the best type for concealment; however, first we had to make it safe for Warfighter use.”
“We will continue to test it for both performance and toxicity until all of our design criteria have been met. The technical approach we took was to make every chemical in the smoke composition perform two functions. For example, the binder not only slows down the burn rate, but also adds to the smoke output,” Domanico said.
Domanico and his team use chemistry to create a safe screening smoke that is still able to produce the correct density of smoke, for a longer amount of time. One of the bonus factors in the proposed overall new grenade design is the ability to use a lid from the M18 series of colored smoke grenades which will completely seal the can from moisture during storage in hot, cold, dry, and humid conditions. This will allow the grenade to last longer in storage and be able to sustain higher abuse prior to use such as deep water immersion. A safe ignition composition designed concurrently with the HX smoke development burns through the sealed metal can, while simultaneously igniting the HX smoke composition.
“Some of the earlier types of grenades were unsafe for Warfighters, because while they were in a screen of smoke, the smoke cloud could irritate skin, or it could be ingested and cause the Warfighter problems under certain conditions. We needed to find ways to be able to use the most effective smoke grenade without similar risks,” Domanico said.
The smoke composition in the current screening grenade is an improved version of a training grenade, which was designed for minimum toxicity at the expense of producing less smoke than the AN-M8 HC grenade. The search has taken the team into an area of increased smoke per unit weight of composition, while maintaining focus on toxicity. Instead of taking a chemical and making a smoke cloud from it, the team produces the smoke chemical as a result of the combustion of two other chemicals.
“Basically, when a smoke cloud has a higher extinction coefficient, you need less of it to screen a particular area. Other factors such as the depth of the smoke cloud, the duration of the smoke particles before they evaporate into the atmosphere and the time the grenade continues to put out smoke particles are all considered in the evaluation of a specific design,” Domanico said.
Domanico said some of the methods used in creating a higher extinction coefficient for the grenade included forming a balance of oxides, which do nothing special for increasing the smoke cloud, and chlorides, that pull water out of the atmosphere and add additional smoke to the existing smoke. Some chlorides under current consideration and testing come from the combustion of powdered metals such as titanium and boron, and certain waxes.
When the team works to improve materials, such as a smoke composition, they use a thermodynamic balancing program to establish a baseline composition. Small-scale testing then determines the best modifications to that baseline composition. During the initial formulation effort, safety testing is performed to determine the new composition’s sensitivity to shock, friction and static discharge.
New compositions that make excellent smoke have often been rejected due to an unacceptable sensitivity to ignition during storage, transportation, and/or handling.
“There still is a lot of trial and error, once you find a material that works well, the next step is figuring out how much of each material you need to use, and what other chemicals you need to put into the grenade to maintain the desired reaction rate,” Domanico said.
Before the actual grenades are made, Domanico and his team conduct an imperial test matrix to measure the relationships between the chemicals, and make sure that the combined chemicals can produce the required effect.
While the chemistry knowledge of the Pyrotechnics and Explosives Branch’s operations is extensive and involves several rounds of trial and error after the initial calculations, the application of other disciplines such as mechanical engineering, drafting and human factors all work together towards creating the highest quality and safest type of smoke grenade for the Warfighter.

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