Army labs join forces for healthier smokes
December 20, 2012
- The U.S. Army is working to make smoke grenades that are safer and just as effective as earlier grenades.
- Collaborative effort includes scientists and engineers at Picatinny Arsenal and Aberdeen Proving Ground, Md.
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PICATINNY ARSENAL, N.J. -- Soldiers know the value of smoke grenades in various scenarios, yet the grenades contained potentially harmful chemicals.
Now, the Army is working to produce pyrotechnic smoke grenades that are not only safer but also as effective as earlier grenades.
A collaborative effort that includes scientists and engineers at Picatinny Arsenal and Aberdeen Proving Ground, Md., is getting closer to solving this problem by developing high-performance smoke compositions without toxic chemicals.
Pyrotechnic smoke is used in combat for signaling, marking targets and positions, and to conceal the movement of vehicles and troops. It can be delivered by grenades, mortar rounds or artillery shells.
SEEKING HIGH PERFORMANCE
"For many years the U.S. Army used high-performance hexachloroethane (HC) smoke compositions, but these are no longer produced because HC is highly toxic," said Anthony P. Shaw, a chemist at Picatinny Arsenal.
"Terephthalic acid (TA) compositions, which are non-toxic, were developed for use in training grenades, but now that the HC items are no longer made, Warfighters have to use the low-performance TA smoke in combat."
So while eliminating the risk of exposure to toxic fumes is a plus, having only the inferior training grenades poses another problem. "The TA smoke grenades can't produce the same thickness and duration of smoke that the old HC ones could," Shaw noted.
Shaw, who works within the Energetics, Warheads and Manufacturing Technology Directorate, Pyrotechnics Division of the U.S. Army Armament Research, Development and Engineering Center (ARDEC), worked with Jay C. Poret, a physical scientist in the same lab, to tackle the problem.
Their work has been funded by the Environmental Quality Technology Program, which falls under the U.S. Army Research, Development and Engineering Command.
Shaw and Poret discovered that smoke compositions containing boron carbide showed promise by giving a good cloud of smoke and leaving little residue behind.
One of their biggest challenges was figuring out how to test the obscuration performance (ability to hide) of the new compositions on a small scale.
"Small-scale testing is a good idea because it's inexpensive relative to large-scale tests," said Poret. "Because we wanted to do the small-scale testing first, we needed to design compositions that were not sensitive to configuration--ones that burn similarly on a small scale as they do on a larger scale."
Pyrotechnic compositions don't always behave the same in small and large-scale tests. The benefit of compositions being "configuration-insensitive" is that scientists can readily predict their performance regardless of the hardware on which they are loaded.
For the initial small-scale tests, Poret designed an advanced optical measurement system for a phone booth-sized smoke chamber, which allowed one or two gram samples to be tested.
ARDEC Pyrotechnics Division is planning to construct a larger 8'x8'x8' smoke chamber in its new $18 million Pyrotechnics Complex that will enable intermediate-scale (10-30 gram) testing. The new Pilot Plant facility will be used for manufacturing future prototype compositions.
Computational methods played an important role in developing the new compositions. According to Poret, this effort is one of only a few examples where combustion-code modeling was used to develop a new pyrotechnic formulation.
"The computational modeling was important for figuring out how to optimize the compositions for efficiency--the more material we can aerosolize in the chemical reaction, the better the smoke cloud," said Poret.
Another challenge was figuring out how to control the burn rate in the new compositions intended to replace the toxic HC and the less effective TA formulations.
"Smoke devices, such as smoke grenades, need to have a specific burning time to be useful for screening," said Shaw. "This factor, the rate or "kinetics" of the system, is not something that our computational methods can easily predict."
Rather than relying on computational methods to solve this problem, success hinged on Shaw's extensive background in chemical kinetics, and Poret's background in materials science, to find the solution.
"We found that small amounts of certain additives can have a profound effect on burning rate," said Shaw. "Not only were we able to get the long burning times we needed for a grenade application, we can also tune the burning rate to suit almost any other smoke munition."
With the small-scale testing completed, it was time to move on to larger-scale evaluations of the new smoke compositions. For that, Shaw and Poret turned to the Edgewood Chemical Biological Center (ECBC) located at Aberdeen Proving Ground, Md.
"ECBC has all the facilities and ranges needed for large-scale smoke testing, including a 190 cubic meter smoke chamber that can be used for testing large prototypes," Shaw explained. "We took our best ARDEC-developed compositions and tested them in full-size grenades at ECBC."
ECBC maintains a full-scale facility known as the Pyrotechnics Complex that can manufacture gram quantities of experimental pyrotechnics as well as prototype devices in excess of 35 kilograms.
"The complex maintains a large collection of buildings containing inert material and precursor chemicals as well as several ammunition bunkers for explosive components and finished items awaiting shipment to customers or testing at ECBC," said Joe Domanico, Pyrotechnics and Explosives Branch Chief at ECBC.
"A large aerosol chamber maintains state of the art characterization equipment, which allows ECBC to completely analyze a new smoke or aerosol's performance along the entire spectrum of interest."
ECBC's mission is to develop new smokes and obscurants and the means to disseminate them to meet current and emerging requirements.
The Research and Technology Directorate (Smoke and Target Defeat Branch) is in charge of the U.S. Army's science and technology efforts in this area and has the unique facilities to evaluate the performance of obscurants.
"Traditionally, in pyrotechnics, ARDEC has been tasked with illumination flares, countermeasures, battlefield effects simulators and signaling/marking smokes, while ECBC's mission has been obscuration smokes," Shaw explained.
The results of the tests at ECBC confirmed the results found in the earlier ARDEC small-scale tests. "It gave us a lot more confidence in the value of our small-scale development approach at ARDEC," said Poret.
"Going forward, we intend to continue prototyping and modifying the compositions at ECBC," said Shaw. "We're also going to be talking to project managers to see which additional munitions we may be able to use this technology in."
While the tests were successful, further research and evaluation must be conducted at ARDEC and ECBC.
"The formulation developed by Tony Shaw is one of several formulations under development and consideration as a new low-hazard visual smoke for hand grenades," said Domanico.
"It is currently competing with other candidates developed by the ECBC Pyrotechnics and Explosives Branch, as well as several other candidate smoke compositions proposed by defense contractors."
With such a high priority on smokes and obscurants, the competition is rigorous to ensure the Warfighter gets the best product possible, not only in performance but also in terms of cost, safety, and environmental impact, Domanico explained.
"Good ideas come from everywhere," said Domanico. "You should always be open to suggestions. Often, a failure in the pursuit of a single problem leads to a solution to an unrelated one.
"Keep track of everything you do in research, as one day that information may hold the key to an answer for another problem."
"There's no reason we can't collaborate, especially when it can lead to a better product for the Warfighter," said Shaw.
Poret added:"By using expertise and facilities at both ARDEC and ECBC, the overall cost and development time to field these items will be reduced, so we'll be able to bring new technologies to the Warfighter faster," .
"It is sometimes forgotten that the Soldier is the big winner in joint research and development efforts," Domanico said.
"When the best of both organizations is applied to a particular problem, the success can be measured in terms of Soldiers' lives that may be saved on the battlefield."