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The Department of Defense (DoD) has many sites that have accumulated a substantial amount of explosives-contaminated scrap metal. Explosive incidents involving scrap metal from training and firing ranges have occurred over the years and, recently, these incidents have come under increased scrutiny for safety reasons. Before commercial release for recycling, DoD policy requires certification that the scrap metal is inert. Currently, this certification is conducted by visual inspection—a process that is subjective, unscientific, and error prone due to an inability to inspect inside cracks, crevices, and internal parts. Increasingly, DoD must address the accumulation of range residues as a potential liability and invest assets to process the materials. Historical decontamination methods—including open burning, open detonation, and flashing—have become virtually unused due to environmental concerns and have created the current safety risk scenario for range personnel and commercial recycling companies. The objective of this project was to demonstrate safe and effective decontamination of range scrap materials at the lowest possible cost.
An effective, environmentally safe alternative to decontaminate firing range scrap is a low temperature (500-600ºF) thermal desorption process called Hot Gas Decontamination (HGD), which was developed by the U.S. Army Environmental Center. In this project, a treatment facility was built on site at the U.S. Army Aberdeen Test Center, located at Aberdeen Proving Ground, Maryland, using locally available materials. The transportable HGD system demonstrated was a gas-fired burner system that heats a pile of explosives-contaminated range residue covered by an insulation blanket. An optimal decontamination system was determined. Optimal decontamination times and temperatures also were determined, and various foundation materials (i.e., the base of the chamber) were tested for effectiveness.
During demonstration of the blanket-on-pile transportable HGD system, spiked coupons were cleaned of all explosive contamination once the pile reached its predetermined temperature and soak time. Decontamination was accomplished by reaching 500ºF with 3 hours of soak time or 600ºF with 2 hours of soak time. The density of the pile determined the time needed to reach the predetermined temperature. Preliminary data showed that a less dense pile, containing reactive armor tile pieces and some split open large caliber projectiles, took 3-4 hours to heat; whereas, a more dense pile, made up of split open large caliber projectiles, took up to 8 hours to heat.
The high cost of building permanent or semi-permanent structures prohibits many installations from using effective decontamination technologies. In comparison to a fixed facility using an HGD furnace, the transportable blanket-on-pile configuration was cheaper to operate and maintain. The transportable blanket-on-pile system was calculated to be $97 per ton compared to $424 per ton for the fixed HGD facility and $1061 per ton for the transportable HGD furnace. In addition, the blanket-on-pile system has no emissions point source and no off-gas treatment system. The demonstrated technology provides an effective, safe, and affordable decontamination process for use by many DoD installations. (Project Completed - 2007)